US20130038131A1 - Semiconductor device to select a power supply - Google Patents
Semiconductor device to select a power supply Download PDFInfo
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- US20130038131A1 US20130038131A1 US13/654,967 US201213654967A US2013038131A1 US 20130038131 A1 US20130038131 A1 US 20130038131A1 US 201213654967 A US201213654967 A US 201213654967A US 2013038131 A1 US2013038131 A1 US 2013038131A1
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- power supply
- voltage
- switch
- node
- external power
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
- G06F1/26—Power supply means, e.g. regulation thereof
- G06F1/263—Arrangements for using multiple switchable power supplies, e.g. battery and AC
Definitions
- the present invention relates to a power supply circuit of portable devices and, particularly, to a circuit of selecting and detecting a power supply.
- Recent information technology devices are reduced in size, and mobile computers, digital cameras, and storage devices with high portability are developed to thereby enable information interchange with interconnection.
- portable devices are small sized to ensure portability, and therefore power is supplied through a power-suppliable interface connector such as an AC adapter or USB (Universal Serial Bus).
- a power-suppliable interface connector such as an AC adapter or USB (Universal Serial Bus).
- Such a power supply system is often designed to, for example, place high priority on a power supply, if any, from a power supply source dedicated to providing a power supply only such as an AC adapter in order to minimize the power consumption of a battery of a host computer or the like which is connected through an interface connector.
- a circuit to detect and select a power supply is placed between a portable device and a power supply source. Power supply selection/detection circuits according to related arts are described hereinafter.
- FIG. 5 is a block diagram of a power supply selection/detection circuit according to a relate art.
- the power supply selection/detection circuit 500 includes a power supply detector 510 disposed between the power supply 511 and the main power supply 502 , and a power supply detector 520 disposed between the power supply 521 and the main power supply 502 .
- the power supply detector 510 includes a Schottky diode 512 , a voltage comparator 513 , and two resistors 514 and 515 .
- the power supply detector 520 includes a Schottky diode 522 , a voltage comparator 523 , and two resistors 524 and 525 .
- the voltage comparator 523 detects if power is supplied through the power supply 521 .
- One input terminal of the voltage comparator 523 receives a reference power supply voltage Vb 1
- the other input terminal of the voltage comparator 523 receives a voltage Vb 2 at a node between the resistors 524 and 525 that divide by resistance the power supply 521 .
- the power supply 511 is described as an AC adapter and the power supply 521 as an USB connector, for example.
- the power supply selection/detection circuit 500 when the voltage supplied from the AC adapter is higher than the voltage supplied from the USB connector, which is when the power supply 511 is higher than the power supply 521 , is described hereinafter.
- the voltage comparator 513 compares the reference voltage Va 1 with the voltage Vat at the node between the resistors 514 and 515 to detect that the power supply 511 is supplied.
- the voltage comparator 523 compares the reference voltage Vb 1 with the voltage Vb 2 at the node between the resistors 524 and 525 to detect if the power supply 521 is supplied. If the power supply 521 is lower than the power supply 511 , the voltage from the power supply 511 is supplied preferentially.
- the operation of the power supply selection/detection circuit 500 when only the power supply voltage from the AC adapter is connected, which is when only the power supply 511 is connected, is described hereinafter.
- the voltage comparator 513 compares the reference voltage Va 1 with the voltage Vat at the node between the resistors 514 and 515 to detect that the power supply 511 is being supplied.
- reverse leakage current Ir from the main power supply 502 flows to the Schottky diode 522 .
- diodes ideally transmit current in one direction only, backward current flows slightly in practice. Accordingly, the voltage Vb 2 occurs at the node between the resistors 524 and 525 .
- the voltage comparator 523 falsely detects that power is being supplied through the power supply 521 . It is therefore necessary to set low values to the resistors 524 and 525 .
- FIG. 6 is a block diagram of a power supply selection/detection circuit disclosed therein.
- the power supply selection/detection circuit illustrated in FIG. 6 includes a power supply line 1 to supply power from an interface such as USB and a power supply line 2 to supply power from an AC adapter.
- power supply from the interface is shut off when power is supplied from the AC adapter.
- the voltage of the power supply line 2 increases, the current flows into the ground through a Zener diode 10 .
- the base voltage of a transistor 17 increases due to the IR drop across a resistor 12 to turn on the transistor 17 .
- the base voltage of a transistor 18 thereby decreases to turn off the transistor 18 , which then turns off a transistor 20 .
- the power supply from the interface is shut off.
- the inventor of the present invention has found that the above-described related arts have the following problems.
- the power supply selection/detection circuit 500 illustrated in FIG. 5 if the voltage supplied from the power supply 511 is higher than the voltage supplied from the power supply 521 , current flows to the resistors 524 and 525 which are connected to the voltage comparator 523 . This raises the problem that current consumption occurs in the power supply detector 520 that is related to the power supply 521 which is not connected with the main power supply 502 . Although the consumption current can be reduced by increasing the resistance of the resistors 524 and 525 , this causes another problem.
- the voltage comparator 523 can falsely detect that power is being supplied through the power supply 521 .
- the resistance of the resistor 525 is Rb 2
- the reverse leakage current of the Schottky diode is Ir
- the reference voltage of the voltage comparator 523 is Vb 1
- the resistance of the resistor 525 cannot be set high enough. This raises the problem that the current consumed in the power supply detector 520 cannot be reduced when power is supplied from the power supply 511 to the main power supply 502 . This not only increases the power consumption in the circuit in the standby mode but also fails to satisfy the current limit Imax of an USB connector in suspend mode if the power supply 521 is a USB connector.
- the similar problem occurs in the configuration of the power supply selection/detection circuit illustrated in FIG. 6 . Because current keeps flowing through the resistors 11 and 12 while the AC adapter is connected, power consumption occurs in a voltage detector 5 . Although the consumption current can be reduced by increasing the resistance of the resistors 11 and 12 , this causes another problem. Specifically, diodes 8 and 9 are placed respectively on the power supply lines 1 and 2 to prevent current backflow. Although the diodes ideally transmit current in one direction only, backward current flows slightly in practice. For example, if power is supplied through the power supply line 1 , the backward current occurs in the diode 9 and flows into the ground through the resistors 11 and 12 .
- a power supply selection/detection circuit to select one main power supply from a plurality of external power supplies, including a resistance element with one end connected to an external power supply and another end connected to the main power supply, a first voltage detector to receive a voltage of the external power supply and detect a voltage of the external power supply, a second voltage detector to detect a voltage between the ends of the resistance element, and a switch connected between the external power supply and a ground to short-circuit or open-circuit between the external power supply and the ground according to an output of the second voltage detector.
- the resistance element and the first voltage detector are disposed for each of the plurality of external power supplies, and the second voltage detector and the switch are disposed for at least one of the plurality of external power supplies. Such a configuration prevents the first voltage detector from falsely detecting an external power supply voltage.
- This configuration enables the resistance of a voltage-dividing resistor that divides by resistance an external power supply voltage to be set high, thereby allowing the provision of a power supply selection/detection circuit with reduced current consumption.
- FIG. 1 shows the configuration of a power supply selection/detection circuit according to a first embodiment of the present invention
- FIG. 4 shows the configuration of a power supply selection/detection circuit according to a third embodiment of the present invention
- FIG. 5 shows the configuration of a power supply selection/detection circuit according to a related art
- FIG. 6 shows the configuration of a power supply selection/detection circuit according to another related art.
- the power supply selection/detection circuit 100 includes a power supply detector 110 disposed between the power supply 111 and the main power supply 102 , and a power supply detector 120 disposed between the power supply 121 and the main power supply 102 .
- the power supply detector 110 includes a Schottky diode 112 , a voltage comparator 113 , and two resistors 114 and 115 .
- the power supply detector 110 includes a voltage detector 119 , which includes the voltage comparator 113 and the two resistors 114 and 115 .
- the power supply detector 120 includes a Schottky diode 122 , two voltage comparators 123 and 126 , three resistors 124 , 125 and 128 , and a switch 127 .
- the power supply detector 120 includes a voltage detector 129 , which includes the voltage comparator 123 and the resistors 124 and 125 .
- the power supply selection/detection circuit 100 supplies power to an external load 103 such as a hard disk drive or a microcomputer through a load 101 such as a DC/DC converter, LDO (Low Drop Out Regulator), or a battery charger.
- the power supply to the load 101 is not limited to the power supplies 111 and 121 and a plurality of power supplies may be added.
- the power supply selection/detection circuit 100 excluding the Schottky diodes 112 and 122 may be formed integrally with an electric circuit of the load 101 on a semiconductor device 104 such as LSI.
- the resistors 114 , 115 , 124 and 125 may be connected outside the semiconductor device 104 .
- the anode of the Schottky diode 112 is connected to the power supply 111 , and the cathode of the Schottky diode 112 is connected to the main power supply 102 .
- the voltage comparator 113 detects the voltage of the power supply 111 to determine the presence or absence of the power supply 111 .
- the voltage comparator 113 receives a reference power supply voltage Va 1 and a voltage Va 2 at a node between the resistors 114 and 115 that divide by resistance the power supply 111 .
- the other end of the resistor 114 is connected to the power supply 111 , and the other end of the resistor 115 is grounded.
- the anode of the Schottky diode 122 is connected to the power supply 121
- the cathode of the Schottky diode 122 is connected to the main power supply 102
- the input terminals of the voltage comparator 126 are respectively connected to the power supply 121 on the anode side of the Schottky diode 122 and the main power supply 102 on the cathode side of the Schottky diode 122 so as to compare a voltage difference between the power supply 121 and the main power supply 102 .
- the output terminal of the voltage comparator 126 is connected to the switch 127 .
- One end of the switch 127 is connected to the power supply 121 , and the other end is grounded through the resistor 128 .
- the switch 127 is short-circuited or open-circuited according to the output from the voltage comparator 126 based on the comparison between the voltage at the anode of the Schottky diode 122 and the voltage at the cathode of the Schottky diode 122 . Specifically, if the voltage of the power supply 121 is lower than the voltage of the main power supply 102 (including when the power supply 121 is not inserted), the switch 127 is short-circuited. If, on the other hand, the voltage of the power supply 121 is higher than the voltage of the main power supply 102 , the switch 127 is open-circuited.
- the resistor 128 connected to the switch 127 has sufficiently low resistance with respect to the resistors 124 and 125 that serve as voltage-dividing resistors for the power supply 121 .
- the resistor 128 is placed to deal with the Schottky diode reverse leakage current Ir, and if the reverse leakage current Ir is 120 ⁇ A or less, it is preferred that the resistance Rb 1 of the resistor 124 is 750 K ⁇ 20%, the resistance Rb 2 of the resistor 125 is 250 K ⁇ 20%, and the resistance Rb 3 of the resistor 128 is 7.5 K ⁇ 20%.
- the power supply selection/detection circuit 100 is described hereinafter with reference to FIG. 1 .
- the power supply 111 is described as an AC adapter and the power supply 121 as an USB connector, for example.
- the voltage of the main power supply 102 is a voltage (e.g. about 0.2V) that is lower than the voltage of the power supply 111 by the amount of the forward voltage drop VF of the Schottky diode 112 due to the PN junction in the Schottky diode 112 .
- the voltage comparator 113 compares the reference voltage Va 1 and the voltage Va 2 at the node to thereby detect that power is being supplied to the power supply 111 .
- the power supply detector 120 a voltage lower than that supplied to the power supply 111 is supplied to the power supply 121 .
- the voltage of the power supply 121 is thereby lower than the voltage of the main power supply 102 , so that the switch 127 is short-circuited according to the output of the voltage comparator 126 .
- the voltage comparator 123 compares the reference voltage Vb 1 and the voltage Vb 2 at the node to thereby determine the presence or absence of the power supply 121 .
- the operation of the power supply selection/detection circuit 100 when only the power supply voltage from the AC adapter is connected, which is when only the power supply 111 is connected, is described hereinafter.
- the voltage of the main power supply 102 is a voltage that is lower than the voltage of the power supply 111 by the amount of VF of the Schottky diode 112 due to the PN junction in the Schottky diode 112 .
- the voltage comparator 113 compares the reference voltage Va 1 and the voltage Va 2 at the node to thereby detect that power is being supplied to the power supply 111 .
- the power supply detector 120 no voltage is supplied to the power supply 121 .
- the voltage of the power supply 121 is thereby lower than the voltage of the main power supply 102 , so that the switch 127 is short-circuited according to the output of the voltage comparator 126 .
- the voltage comparator 123 compares the reference voltage Vb 1 and the voltage Vb 2 at the node to thereby determine that there is no power supply 121 .
- the reverse leakage current Ir from the main power supply 102 flows into the Schottky diode 122 .
- the resistor 128 connected to the switch 127 has sufficiently low resistance with respect to the resistors 124 and 125 . Accordingly, the reverse leakage current Ir flows into the resistor 128 through the short-circuited switch 127 . This prevents the reverse leakage current Ir from flowing into the node between the resistors 124 and 125 . Therefore, the voltage Vb 2 at the node does not exceed the reference voltage Vb 1 , thereby avoiding the false detection in the voltage comparator 123 .
- the power supply 111 is an AC adapter that is a dedicated line for power supply, it is possible to form a circuit that preferentially supplies the power from the power supply 111 to the main power supply 102 when power is connected to the power supply 111 .
- a transistor 203 is connected between the cathode of the Schottky diode 122 and the main power supply 102 .
- the gate terminal of the transistor 203 is connected to the output terminal of the voltage comparator 113 of the power supply detector 110 .
- the transistor 203 opens and closes according to the output from the voltage comparator 113 and, if power is connected to the power supply 111 , the power from the power supply 111 is supplied preferentially.
- the polarity of the transistor 203 may be N-channel or P-channel.
- a resistor 202 to be used for current detection or the like may be placed on the cathode side of the Schottky diode 122 .
- one end of the resistor 202 is connected to the cathode of the Schottky diode 122 , and the other end of the resistor 202 is connected to the transistor 203 .
- the voltage comparator 126 detects the presence of absence of an external power supply using a voltage difference after the VF drop due to the PN junction in the Schottky diode 122 , it is possible to use a voltage difference between the both ends of the resistor 202 or a voltage difference between the terminals of the transistor 203 shown in FIG. 2 . It is also possible to use a voltage difference between the Schottky diode 122 and the resistor 202 , a voltage difference between the resistor 202 and the transistor 203 , or a voltage difference between the Schottky diode 122 and the transistor 203 .
- the switch 127 which opens and closes according to a voltage difference between the anode and the cathode of the Schottky diode 122 and the resistor 128 . Because the reverse leakage current Ir does not flow into the node between the resistors 124 and 125 , the voltage comparator 123 does not falsely detect that a voltage is being supplied to the power supply 121 .
- the resistance of the resistors 124 and 125 can be therefore set high, which enables the reduction of the current consumed in the resistors 124 and 125 . This reduces the power consumption in the power supply detector 120 in the standby mode or suspend mode that is related to the power supply 121 which is not connected with the main power supply 102 .
- the resistance of the resistor 124 is Rb 1
- the resistance of the resistor 125 is Rb 2
- the current limit of the power supply 121 in the standby or suspend mode is Imax
- the supply voltage of the power supply 121 is V
- the resistance of the resistors 124 and 125 can be set to satisfy the equation: V/Imax ⁇ (Rb 1 +Rb 2 ).
- the current limit can be satisfied by increasing the resistance of the resistors 124 and 125 . This is particularly effective when the power supply 121 is a USB connector, for example.
- the value of Rb 1 +Rb 2 is preferably 8.6 to 10.8 K ⁇ or higher to satisfy the expression V/Imax ⁇ (Rb 1 +Rb 2 ).
- the circuit to which the USB connector supplies a voltage during the suspend mode is not only the power supply selection/detection circuit. Accordingly, the value of Rb 1 +Rb 2 is preferably 43 to 54 K ⁇ or higher (Imax is 100 ⁇ A or less) and more preferably 1 M ⁇ or higher (Imax is 4.3 to 5.4 ⁇ A or less).
- FIG. 3 shows the configuration of the power supply selection/detection circuit according to the second embodiment.
- the same circuit elements or operating principles as in the first embodiment are not described herein.
- the power supply selection/detection circuit 300 includes a power supply detector 310 disposed between the power supply 111 and the main power supply 102 , and the power supply detector 120 disposed between the power supply 121 and the main power supply 102 .
- the power supply detector 310 includes a voltage comparator 316 , a resistor 318 , and a switch 317 .
- the other configuration is the same as that in the power supply selection/detection circuit 100 of the first embodiment.
- the power supply selection/detection circuit 300 supplies power to the external load 103 such as a hard disk drive or a microcomputer through the load 101 such as a DC/DC converter, LDO, or a battery charger.
- the power supply to the load 101 is not limited to the power supplies 111 and 121 and a plurality of power supplies may be added.
- the power supply selection/detection circuit 300 excluding the Schottky diodes 112 and 122 may be formed integrally with an electric circuit of the load 101 on a semiconductor device such as LSI, and the resistors 114 , 115 , 124 and 125 may be connected outside the semiconductor device.
- the anode of the Schottky diode 112 is connected to the power supply 111
- the cathode of the Schottky diode 112 is connected to the main power supply 102 .
- the input terminal of the voltage comparator 316 is connected to the power supply 111 on the anode side of the Schottky diode 112
- the other input terminal of the voltage comparator 316 is connected to the main power supply 102 on the cathode side of the Schottky diode 112 so as to compare a voltage difference between the power supply 111 and the main power supply 102 .
- the output terminal of the voltage comparator 316 is connected to the switch 317 .
- the switch 317 is short-circuited or open-circuited according to the output from the voltage comparator 316 based on the comparison between the voltage at the anode of the Schottky diode 112 and the voltage at the cathode of the Schottky diode 112 . Specifically, if the voltage of the power supply 111 is lower than the voltage of the main power supply 102 (including when the power supply 111 is not inserted), the switch 317 is short-circuited. If, on the other hand, the voltage of the power supply 111 is higher than the voltage of the main power supply 102 , the switch 317 is open-circuited. The operation of the switch 127 is the same as that of the first embodiment.
- the power supply detector 120 a voltage lower than that supplied to the power supply 111 is supplied to the power supply 121 .
- the voltage of the power supply 121 is thereby lower than the voltage of the main power supply 102 , so that the switch 127 is short-circuited according to the output of the voltage comparator 126 .
- the voltage comparator 123 compares the reference voltage Vb 1 and the voltage Vb 2 at the node to thereby determine the presence or absence of the power supply 121 .
- the power supply detector 120 no voltage is supplied to the power supply 121 .
- the voltage of the power supply 121 is thereby lower than the voltage of the main power supply 102 , so that the switch 127 is short-circuited according to the output of the voltage comparator 126 .
- the voltage comparator 123 compares the reference voltage Vb 1 and the voltage Vb 2 at the node to thereby determine that there is no power supply 121 .
- the switch 317 is open-circuited in the power supply detector 310 related to the power supply 111 which is connected to the main power supply 102 , no current flows into the voltage comparator 316 and the resistor 318 . Accordingly, adding the voltage comparator 316 , the resistor 318 and the switch 317 to the power supply detector 310 does not cause an increase in power consumption.
- FIG. 4 shows the configuration of the power supply selection/detection circuit according to the third embodiment. The same circuit elements or operating principles as in the first embodiment are not described herein.
- the power supply selection/detection circuit 400 includes a power supply detector 410 disposed between the power supply 411 and the main power supply 402 , and a power supply detector 420 disposed between the power supply 421 and the main power supply 402 .
- the power supply detector 410 includes a Schottky diode 412 , two voltage comparators 413 and 416 , two resistors 414 and 415 , and a switch 417 .
- the power supply detector 410 includes a voltage detector 419 , which includes the voltage comparator 413 and the two resistors 414 and 415 .
- the power supply detector 420 includes a Schottky diode 422 , two voltage comparators 423 and 426 , and two resistors 424 and 425 , and a switch 427 .
- the power supply detector 420 includes a voltage detector 429 , which includes the voltage comparator 423 and the resistors 424 and 425 .
- the power supply selection/detection circuit 400 supplies power to an external load (not shown) such as a hard disk drive or a microcomputer through the load 401 such as a DC/DC converter, LDO, or a battery charger as described in the first embodiment.
- the power supply to the load 401 is not limited to the power supplies 411 and 421 and a plurality of power supplies may be added.
- the power supply selection/detection circuit 400 excluding the Schottky diodes 412 and 422 may be formed integrally with an electric circuit of the load 401 on a semiconductor device such as LSI, and the resistors 414 , 415 , 424 and 425 may be connected outside the semiconductor device as described in the first embodiment.
- the switch 427 may be placed between the resistor 424 and the input terminal of the voltage comparator 423 . Further, the switch 427 may be placed between the input terminal of the voltage comparator 423 and the resistor 425 , or between the resistor 425 and the ground.
- the switch 427 is short-circuited or open-circuited according to the output from the voltage comparator 426 based on the comparison between the voltage at the anode of the Schottky diode 422 and the voltage at the cathode of the Schottky diode 422 . Specifically, if the voltage of the power supply 421 is lower than the voltage of the main power supply 402 (including when the power supply 421 is not inserted), the switch 427 is open-circuited. If, on the other hand, the voltage of the power supply 421 is higher than the voltage of the main power supply 402 , the switch 427 is short-circuited.
- the power supply selection/detection circuit 400 is described hereinafter with reference to FIG. 4 .
- the power supply 411 is described as an AC adapter and the power supply 421 as an USB connector, for example.
- the voltage of the main power supply 402 is a voltage that is lower than the voltage of the power supply 411 by the amount of the VF of the Schottky diode 412 due to the PN junction in the Schottky diode 412 .
- the voltage of the power supply 411 is thereby higher than the voltage of the main power supply 402 , and the switch 417 is short-circuited according to the output from the voltage comparator 416 . Accordingly, current flows from the power supply 411 to the ground through the resistors 414 and 415 .
- the voltage Va 2 at the node is thereby higher than the reference voltage Va 1 , and the voltage comparator 413 detects that power is being supplied to the power supply 411 .
- the power supply detector 420 a voltage lower than that supplied to the power supply 411 is supplied to the power supply 421 .
- the voltage of the power supply 421 is thereby lower than the voltage of the main power supply 402 , so that the switch 427 is open-circuited according to the output of the voltage comparator 426 . Accordingly, the voltage Va 2 at the node does not increase but stays at the ground level, and thereby the power supply detector 420 does not detect that power is being supplied to the power supply 421 based on the comparison result in the voltage comparator 423 .
- the power supply detector 420 no voltage is supplied to the power supply 421 .
- the voltage of the power supply 421 is thereby lower than the voltage of the main power supply 402 , so that the switch 427 is open-circuited according to the output of the voltage comparator 426 .
- the voltage Va 2 at the node does not increase but stays at the ground level, so that the power supply detector 420 does not detect that power is being supplied to the power supply 421 based on the comparison result in the voltage comparator 423 .
- the switch 427 is placed between the voltage comparator 423 and the ground, though not shown, the voltage Va 2 at the node is fixed to about a power supply voltage level while the switch 427 is open-circuited.
- the power supply detector 420 can invert the logic of the voltage comparator 423 so as not to detect that power is being supplied to the power supply 421 .
- the power supply selection/detection circuit 400 shown in FIG. 4 may include the transistor 203 and the resistor 202 shown in FIG. 2 (not shown in FIG. 4 ) between the Schottky diode 422 and the main power supply 402 .
- the voltage comparator 426 can determine the presence or absence of an external power supply using not only a voltage difference after the VF drop due to the PN junction in the Schottky diode 422 , but also a voltage difference between the both ends of the resistor or a voltage difference between the terminals of the transistor.
- the present invention is particularly suitable for application to portable devices or the like, and may be applied to any devices to which power is supplied from external sources.
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Abstract
A power supply selection/detection circuit to select one main power supply from a plurality of external power supplies includes a resistance element with one end connected to an external power supply and another end connected to the main power supply, a first voltage detector to receive a voltage of the external power supply and detect a voltage of the external power supply, a second voltage detector to detect a voltage between the ends of the resistance element, and a switch connected between the external power supply and a ground to short-circuit or open-circuit between the external power supply and the ground according to an output of the second voltage detector. The resistance element and the first voltage detector are disposed for each of the plurality of external power supplies, and the second voltage detector and the switch are disposed for at least one of the plurality of external power supplies.
Description
- 1. Field of the Invention
- The present invention relates to a power supply circuit of portable devices and, particularly, to a circuit of selecting and detecting a power supply.
- 2. Description of Related Art
- Recent information technology devices are reduced in size, and mobile computers, digital cameras, and storage devices with high portability are developed to thereby enable information interchange with interconnection. Such portable devices are small sized to ensure portability, and therefore power is supplied through a power-suppliable interface connector such as an AC adapter or USB (Universal Serial Bus).
- Such a power supply system is often designed to, for example, place high priority on a power supply, if any, from a power supply source dedicated to providing a power supply only such as an AC adapter in order to minimize the power consumption of a battery of a host computer or the like which is connected through an interface connector. For instance, a circuit to detect and select a power supply is placed between a portable device and a power supply source. Power supply selection/detection circuits according to related arts are described hereinafter.
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FIG. 5 is a block diagram of a power supply selection/detection circuit according to a relate art. In the power supply selection/detection circuit 500, a voltage supplied from apower supply 511 or a power supply 521 is applied to aload 501 through amain power supply 502. The power supply selection/detection circuit 500 includes apower supply detector 510 disposed between thepower supply 511 and themain power supply 502, and apower supply detector 520 disposed between the power supply 521 and themain power supply 502. Thepower supply detector 510 includes a Schottkydiode 512, avoltage comparator 513, and tworesistors 514 and 515. Thepower supply detector 520 includes a Schottkydiode 522, avoltage comparator 523, and tworesistors - The anode of the Schottky
diode 512 is connected to thepower supply 511, and the cathode of the Schottkydiode 512 is connected to themain power supply 502. Thevoltage comparator 513 detects the voltage of thepower supply 511 to determine the presence or absence of thepower supply 511. Thevoltage comparator 513 receives a reference power supply voltage Va1 and a voltage Va2 at a node between theresistors 514 and 515 that divide by resistance thepower supply 511. The anode of the Schottkydiode 522 is connected to the power supply 521, and the cathode of the Schottkydiode 522 is connected to themain power supply 502. Thevoltage comparator 523 detects if power is supplied through the power supply 521. One input terminal of thevoltage comparator 523 receives a reference power supply voltage Vb1, and the other input terminal of thevoltage comparator 523 receives a voltage Vb2 at a node between theresistors - In this example, the
power supply 511 is described as an AC adapter and the power supply 521 as an USB connector, for example. Thus, when power is supplied from an AC adapter, power supply from an interface is shut off, for instance. The operation of the power supply selection/detection circuit 500 when the voltage supplied from the AC adapter is higher than the voltage supplied from the USB connector, which is when thepower supply 511 is higher than the power supply 521, is described hereinafter. Thevoltage comparator 513 compares the reference voltage Va1 with the voltage Vat at the node between theresistors 514 and 515 to detect that thepower supply 511 is supplied. On the other hand, thevoltage comparator 523 compares the reference voltage Vb1 with the voltage Vb2 at the node between theresistors power supply 511, the voltage from thepower supply 511 is supplied preferentially. - The operation of the power supply selection/
detection circuit 500 when only the power supply voltage from the AC adapter is connected, which is when only thepower supply 511 is connected, is described hereinafter. Thevoltage comparator 513 compares the reference voltage Va1 with the voltage Vat at the node between theresistors 514 and 515 to detect that thepower supply 511 is being supplied. On the other hand, reverse leakage current Ir from themain power supply 502 flows to the Schottkydiode 522. Although diodes ideally transmit current in one direction only, backward current flows slightly in practice. Accordingly, the voltage Vb2 occurs at the node between theresistors voltage comparator 523 falsely detects that power is being supplied through the power supply 521. It is therefore necessary to set low values to theresistors - Another example of a power supply selection/detection circuit is disclosed in Japanese Unexamined Patent Application Publication No. 2000-284865.
FIG. 6 is a block diagram of a power supply selection/detection circuit disclosed therein. The power supply selection/detection circuit illustrated inFIG. 6 includes a power supply line 1 to supply power from an interface such as USB and apower supply line 2 to supply power from an AC adapter. In this circuit also, power supply from the interface is shut off when power is supplied from the AC adapter. Thus, if the voltage of thepower supply line 2 increases, the current flows into the ground through a Zenerdiode 10. Accordingly, the base voltage of a transistor 17 increases due to the IR drop across a resistor 12 to turn on the transistor 17. The base voltage of atransistor 18 thereby decreases to turn off thetransistor 18, which then turns off atransistor 20. As a result, the power supply from the interface is shut off. - However, the inventor of the present invention has found that the above-described related arts have the following problems. In the power supply selection/
detection circuit 500 illustrated inFIG. 5 , if the voltage supplied from thepower supply 511 is higher than the voltage supplied from the power supply 521, current flows to theresistors voltage comparator 523. This raises the problem that current consumption occurs in thepower supply detector 520 that is related to the power supply 521 which is not connected with themain power supply 502. Although the consumption current can be reduced by increasing the resistance of theresistors power supply 511 only, the reverse leakage current Ir from themain power supply 502 flows to the Schottkydiode 522, and the voltage Vb2 occurs at the node between theresistors voltage comparator 523 can falsely detect that power is being supplied through the power supply 521. - To avoid this, if the resistance of the
resistor 525 is Rb2, the reverse leakage current of the Schottky diode is Ir, the reference voltage of thevoltage comparator 523 is Vb1, it is necessary to set the resistance of theresistor 525 to satisfy the expression: Rb2*Ir<Vb1, and therefore the resistance of theresistor 525 cannot be set high enough. This raises the problem that the current consumed in thepower supply detector 520 cannot be reduced when power is supplied from thepower supply 511 to themain power supply 502. This not only increases the power consumption in the circuit in the standby mode but also fails to satisfy the current limit Imax of an USB connector in suspend mode if the power supply 521 is a USB connector. - The similar problem occurs in the configuration of the power supply selection/detection circuit illustrated in
FIG. 6 . Because current keeps flowing through the resistors 11 and 12 while the AC adapter is connected, power consumption occurs in avoltage detector 5. Although the consumption current can be reduced by increasing the resistance of the resistors 11 and 12, this causes another problem. Specifically, diodes 8 and 9 are placed respectively on thepower supply lines 1 and 2 to prevent current backflow. Although the diodes ideally transmit current in one direction only, backward current flows slightly in practice. For example, if power is supplied through the power supply line 1, the backward current occurs in the diode 9 and flows into the ground through the resistors 11 and 12. Then, even though no power is supplied through thepower supply line 2, the base voltage of the transistor 17 increases due to the IR drop across the resistor 12. This turns off thetransistor 18 and further turns off thetransistor 20; as a result, the power supply from thepower supply line 2 is shut off. To avoid this, the resistance of the resistor 12 cannot be set high enough. Consequently, the current consumed in the power supply selection/detection circuit cannot be reduced. - According to one aspect of the present invention, there is provided a power supply selection/detection circuit to select one main power supply from a plurality of external power supplies, including a resistance element with one end connected to an external power supply and another end connected to the main power supply, a first voltage detector to receive a voltage of the external power supply and detect a voltage of the external power supply, a second voltage detector to detect a voltage between the ends of the resistance element, and a switch connected between the external power supply and a ground to short-circuit or open-circuit between the external power supply and the ground according to an output of the second voltage detector. The resistance element and the first voltage detector are disposed for each of the plurality of external power supplies, and the second voltage detector and the switch are disposed for at least one of the plurality of external power supplies. Such a configuration prevents the first voltage detector from falsely detecting an external power supply voltage.
- This configuration enables the resistance of a voltage-dividing resistor that divides by resistance an external power supply voltage to be set high, thereby allowing the provision of a power supply selection/detection circuit with reduced current consumption.
- The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
-
FIG. 1 shows the configuration of a power supply selection/detection circuit according to a first embodiment of the present invention; -
FIG. 2 shows the detailed configuration of a power supply selection/detection circuit according to the first embodiment of the present invention; -
FIG. 3 shows the configuration of a power supply selection/detection circuit according to a second embodiment of the present invention; -
FIG. 4 shows the configuration of a power supply selection/detection circuit according to a third embodiment of the present invention; -
FIG. 5 shows the configuration of a power supply selection/detection circuit according to a related art; and -
FIG. 6 shows the configuration of a power supply selection/detection circuit according to another related art. - The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teaching of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.
- Exemplary embodiments of the present invention are described hereinafter. The following description and the attached drawings are appropriately shortened and simplified to clarify the explanation. Redundant description is omitted as needed to clarify the explanation.
- A first embodiment of the present invention is described hereinafter with reference to the drawings. A power supply selection/detection circuit according to this embodiment is described, by way of illustration, as a circuit which includes, as a load, a driver of a hard disk drive or microcomputer of a portable device and which is formed on a semiconductor device such as an LSI (Large Scale Integration) circuit.
FIG. 1 shows the configuration of a power supply selection/detection circuit according to the first embodiment. - Referring first to
FIG. 1 , in a power supply selection/detection circuit 100, the voltage supplied from a power supply 111 or apower supply 121 is applied to aload 101 through amain power supply 102. The power supply selection/detection circuit 100 includes apower supply detector 110 disposed between the power supply 111 and themain power supply 102, and apower supply detector 120 disposed between thepower supply 121 and themain power supply 102. Thepower supply detector 110 includes aSchottky diode 112, avoltage comparator 113, and tworesistors power supply detector 110 includes avoltage detector 119, which includes thevoltage comparator 113 and the tworesistors - The
power supply detector 120 includes aSchottky diode 122, twovoltage comparators resistors switch 127. Thepower supply detector 120 includes avoltage detector 129, which includes thevoltage comparator 123 and theresistors - The power supply selection/
detection circuit 100 supplies power to anexternal load 103 such as a hard disk drive or a microcomputer through aload 101 such as a DC/DC converter, LDO (Low Drop Out Regulator), or a battery charger. The power supply to theload 101 is not limited to the power supplies 111 and 121 and a plurality of power supplies may be added. The power supply selection/detection circuit 100 excluding theSchottky diodes load 101 on asemiconductor device 104 such as LSI. Theresistors semiconductor device 104. - The anode of the
Schottky diode 112 is connected to the power supply 111, and the cathode of theSchottky diode 112 is connected to themain power supply 102. Thevoltage comparator 113 detects the voltage of the power supply 111 to determine the presence or absence of the power supply 111. Thevoltage comparator 113 receives a reference power supply voltage Va1 and a voltage Va2 at a node between theresistors resistor 114 is connected to the power supply 111, and the other end of theresistor 115 is grounded. - The anode of the
Schottky diode 122 is connected to thepower supply 121, and the cathode of theSchottky diode 122 is connected to themain power supply 102. The input terminals of thevoltage comparator 126 are respectively connected to thepower supply 121 on the anode side of theSchottky diode 122 and themain power supply 102 on the cathode side of theSchottky diode 122 so as to compare a voltage difference between thepower supply 121 and themain power supply 102. The output terminal of thevoltage comparator 126 is connected to theswitch 127. One end of theswitch 127 is connected to thepower supply 121, and the other end is grounded through theresistor 128. Theresistor 128 may be placed between theswitch 127 and thepower supply 121. Thevoltage comparator 123 detects the voltage of thepower supply 121 to determine the presence or absence of thepower supply 121. Thevoltage comparator 123 receives a reference power supply voltage Vb1 and a voltage Vb2 at a node between theresistors power supply 121. The other end of theresistor 124 is connected to thepower supply 121, and the other end of theresistor 125 is grounded. - The
switch 127 is short-circuited or open-circuited according to the output from thevoltage comparator 126 based on the comparison between the voltage at the anode of theSchottky diode 122 and the voltage at the cathode of theSchottky diode 122. Specifically, if the voltage of thepower supply 121 is lower than the voltage of the main power supply 102 (including when thepower supply 121 is not inserted), theswitch 127 is short-circuited. If, on the other hand, the voltage of thepower supply 121 is higher than the voltage of themain power supply 102, theswitch 127 is open-circuited. - The
resistor 128 connected to theswitch 127 has sufficiently low resistance with respect to theresistors power supply 121. Theresistor 128 is placed to deal with the Schottky diode reverse leakage current Ir, and if the reverse leakage current Ir is 120 μA or less, it is preferred that the resistance Rb1 of theresistor 124 is 750 KΩ±20%, the resistance Rb2 of theresistor 125 is 250 KΩ±20%, and the resistance Rb3 of theresistor 128 is 7.5 KΩ±20%. - The operation of the power supply selection/
detection circuit 100 is described hereinafter with reference toFIG. 1 . In this embodiment, the power supply 111 is described as an AC adapter and thepower supply 121 as an USB connector, for example. The operation of the power supply selection/detection circuit 100 when the voltage supplied from the AC adapter is higher than the voltage supplied from the USB connector, which is when the power supply 111 is higher than thepower supply 121, is described firstly. - When a voltage is supplied to the power supply 111, the voltage of the
main power supply 102 is a voltage (e.g. about 0.2V) that is lower than the voltage of the power supply 111 by the amount of the forward voltage drop VF of theSchottky diode 112 due to the PN junction in theSchottky diode 112. Thevoltage comparator 113 compares the reference voltage Va1 and the voltage Va2 at the node to thereby detect that power is being supplied to the power supply 111. - On the other hand, in the
power supply detector 120, a voltage lower than that supplied to the power supply 111 is supplied to thepower supply 121. The voltage of thepower supply 121 is thereby lower than the voltage of themain power supply 102, so that theswitch 127 is short-circuited according to the output of thevoltage comparator 126. Thevoltage comparator 123 compares the reference voltage Vb1 and the voltage Vb2 at the node to thereby determine the presence or absence of thepower supply 121. - Referring still to
FIG. 1 , the operation of the power supply selection/detection circuit 100 when only the power supply voltage from the AC adapter is connected, which is when only the power supply 111 is connected, is described hereinafter. When a voltage is supplied to the power supply 111, the voltage of themain power supply 102 is a voltage that is lower than the voltage of the power supply 111 by the amount of VF of theSchottky diode 112 due to the PN junction in theSchottky diode 112. Thevoltage comparator 113 compares the reference voltage Va1 and the voltage Va2 at the node to thereby detect that power is being supplied to the power supply 111. - On the other hand, in the
power supply detector 120, no voltage is supplied to thepower supply 121. The voltage of thepower supply 121 is thereby lower than the voltage of themain power supply 102, so that theswitch 127 is short-circuited according to the output of thevoltage comparator 126. Thevoltage comparator 123 compares the reference voltage Vb1 and the voltage Vb2 at the node to thereby determine that there is nopower supply 121. - The reverse leakage current Ir from the
main power supply 102 flows into theSchottky diode 122. Theresistor 128 connected to theswitch 127 has sufficiently low resistance with respect to theresistors resistor 128 through the short-circuitedswitch 127. This prevents the reverse leakage current Ir from flowing into the node between theresistors voltage comparator 123. - If the power supply 111 is an AC adapter that is a dedicated line for power supply, it is possible to form a circuit that preferentially supplies the power from the power supply 111 to the
main power supply 102 when power is connected to the power supply 111. For example, in the power supply selection/detection circuit 100 illustrated inFIG. 2 , atransistor 203 is connected between the cathode of theSchottky diode 122 and themain power supply 102. The gate terminal of thetransistor 203 is connected to the output terminal of thevoltage comparator 113 of thepower supply detector 110. In this configuration, thetransistor 203 opens and closes according to the output from thevoltage comparator 113 and, if power is connected to the power supply 111, the power from the power supply 111 is supplied preferentially. The polarity of thetransistor 203 may be N-channel or P-channel. Further, a resistor 202 to be used for current detection or the like may be placed on the cathode side of theSchottky diode 122. Preferably, one end of the resistor 202 is connected to the cathode of theSchottky diode 122, and the other end of the resistor 202 is connected to thetransistor 203. - Although the
voltage comparator 126 detects the presence of absence of an external power supply using a voltage difference after the VF drop due to the PN junction in theSchottky diode 122, it is possible to use a voltage difference between the both ends of the resistor 202 or a voltage difference between the terminals of thetransistor 203 shown inFIG. 2 . It is also possible to use a voltage difference between theSchottky diode 122 and the resistor 202, a voltage difference between the resistor 202 and thetransistor 203, or a voltage difference between theSchottky diode 122 and thetransistor 203. - As described above, it is possible to prevent the reverse leakage current Ir of the
Schottky diode 122 from flowing into theresistors switch 127 which opens and closes according to a voltage difference between the anode and the cathode of theSchottky diode 122 and theresistor 128. Because the reverse leakage current Ir does not flow into the node between theresistors voltage comparator 123 does not falsely detect that a voltage is being supplied to thepower supply 121. The resistance of theresistors resistors power supply detector 120 in the standby mode or suspend mode that is related to thepower supply 121 which is not connected with themain power supply 102. - The case where there is a limit to the current of the
power supply 121 in the standby mode or suspend mode is described hereinbelow. If the resistance of theresistor 124 is Rb1, the resistance of theresistor 125 is Rb2, the current limit of thepower supply 121 in the standby or suspend mode is Imax, and the supply voltage of thepower supply 121 is V, the resistance of theresistors resistors power supply 121 is a USB connector, for example. - To meet the standards of USB connectors, if a supply voltage is 4.3 to 5.4 V and a current limit Imax is 500 μA, the value of Rb1+Rb2 is preferably 8.6 to 10.8 KΩ or higher to satisfy the expression V/Imax≦(Rb1+Rb2). However, the circuit to which the USB connector supplies a voltage during the suspend mode is not only the power supply selection/detection circuit. Accordingly, the value of Rb1+Rb2 is preferably 43 to 54 KΩ or higher (Imax is 100 μA or less) and more preferably 1 MΩ or higher (Imax is 4.3 to 5.4 μA or less).
- A second embodiment of the present invention is described hereinafter with reference to the drawings. In the second embodiment, as in the first embodiment, a power supply selection/detection circuit is described, by way of illustration, as a circuit which includes, as a load, a driver of a hard disk drive or microcomputer of a portable device and which is formed on a semiconductor device such as an LSI.
FIG. 3 shows the configuration of the power supply selection/detection circuit according to the second embodiment. The same circuit elements or operating principles as in the first embodiment are not described herein. - Referring to
FIG. 3 , in a power supply selection/detection circuit 300, the voltage supplied from the power supply 111 or thepower supply 121 is applied to theload 101 through themain power supply 102. The power supply selection/detection circuit 300 includes apower supply detector 310 disposed between the power supply 111 and themain power supply 102, and thepower supply detector 120 disposed between thepower supply 121 and themain power supply 102. Thepower supply detector 310 includes avoltage comparator 316, aresistor 318, and aswitch 317. The other configuration is the same as that in the power supply selection/detection circuit 100 of the first embodiment. - The power supply selection/
detection circuit 300 supplies power to theexternal load 103 such as a hard disk drive or a microcomputer through theload 101 such as a DC/DC converter, LDO, or a battery charger. As described in the first embodiment, the power supply to theload 101 is not limited to the power supplies 111 and 121 and a plurality of power supplies may be added. Further, as in the first embodiment, the power supply selection/detection circuit 300 excluding theSchottky diodes load 101 on a semiconductor device such as LSI, and theresistors - The anode of the
Schottky diode 112 is connected to the power supply 111, and the cathode of theSchottky diode 112 is connected to themain power supply 102. The input terminal of thevoltage comparator 316 is connected to the power supply 111 on the anode side of theSchottky diode 112, and the other input terminal of thevoltage comparator 316 is connected to themain power supply 102 on the cathode side of theSchottky diode 112 so as to compare a voltage difference between the power supply 111 and themain power supply 102. The output terminal of thevoltage comparator 316 is connected to theswitch 317. One end of theswitch 317 is connected to the power supply 111, and the other end is grounded through theresistor 318. Theresistor 318 may be placed between theswitch 317 and the power supply 111. Thevoltage comparator 113 detects the voltage of the power supply 111 to determine the presence or absence of the power supply 111. Thevoltage comparator 113 receives a reference power supply voltage Vb1 and a voltage Vb2 at a node between theresistors resistor 114 is connected to the power supply 111, and the other end of theresistor 115 is grounded. - The
switch 317 is short-circuited or open-circuited according to the output from thevoltage comparator 316 based on the comparison between the voltage at the anode of theSchottky diode 112 and the voltage at the cathode of theSchottky diode 112. Specifically, if the voltage of the power supply 111 is lower than the voltage of the main power supply 102 (including when the power supply 111 is not inserted), theswitch 317 is short-circuited. If, on the other hand, the voltage of the power supply 111 is higher than the voltage of themain power supply 102, theswitch 317 is open-circuited. The operation of theswitch 127 is the same as that of the first embodiment. - The
resistor 318 connected to theswitch 317 has sufficiently low resistance with respect to theresistors resistor 318 is placed to deal with the reverse leakage current Ir of the Schottky diode, and if the reverse leakage current Ir is 120 μA or less, it is preferred that the resistance Ra1 of theresistor 114 is 750 KΩ±20%, the resistance Ra2 of theresistor 115 is 250 KΩ±20%, and the resistance Ra1 of theresistor 318 is 7.5 KΩ±20%. - The operation of the power supply selection/
detection circuit 300 is described hereinafter with reference toFIG. 3 . In this embodiment, the power supply 111 is described as an AC adapter and thepower supply 121 as an USB connector, for example. The operation of the power supply selection/detection circuit 300 when the voltage supplied from the AC adapter is higher than the voltage supplied from the USB connector, which is when the power supply 111 is higher than thepower supply 121, is described firstly. - When a voltage is supplied to the power supply 111, the voltage of the
main power supply 102 is a voltage that is lower than the voltage of the power supply 111 by the amount of the VF of theSchottky diode 112 due to the PN junction in theSchottky diode 112. The voltage of the power supply 111 is thereby higher than the voltage of themain power supply 102, and theswitch 317 is open-circuited according to the output from thevoltage comparator 316. Thevoltage comparator 113 compares the reference voltage Va1 and the voltage Va2 at the node to thereby detect that power is being supplied to the power supply 111. - On the other hand, in the
power supply detector 120, a voltage lower than that supplied to the power supply 111 is supplied to thepower supply 121. The voltage of thepower supply 121 is thereby lower than the voltage of themain power supply 102, so that theswitch 127 is short-circuited according to the output of thevoltage comparator 126. Thevoltage comparator 123 compares the reference voltage Vb1 and the voltage Vb2 at the node to thereby determine the presence or absence of thepower supply 121. - Referring still to
FIG. 3 , the operation of the power supply selection/detection circuit 300 when only the power supply voltage from the AC adapter is connected, which is when only the power supply 111 is connected, is described hereinafter. When a voltage is supplied to the power supply 111, the voltage of themain power supply 102 is a voltage that is lower than the voltage of the power supply 111 by the amount of VF of theSchottky diode 112 due to the PN junction in theSchottky diode 112 in thepower supply detector 310. Accordingly, the voltage of the power supply 111 is higher than the voltage of themain power supply 102, and theswitch 317 is open-circuited according to the output from thevoltage comparator 316. Thevoltage comparator 113 compares the reference voltage Va1 and the voltage Va2 at the node to thereby detect that power is being supplied to the power supply 111. - On the other hand, in the
power supply detector 120, no voltage is supplied to thepower supply 121. The voltage of thepower supply 121 is thereby lower than the voltage of themain power supply 102, so that theswitch 127 is short-circuited according to the output of thevoltage comparator 126. Thevoltage comparator 123 compares the reference voltage Vb1 and the voltage Vb2 at the node to thereby determine that there is nopower supply 121. - The reverse leakage current Ir from the
main power supply 102 flows into theSchottky diode 122. Theresistor 128 connected to theswitch 127 has sufficiently low resistance with respect to theresistors resistor 128 through the short-circuitedswitch 127. This prevents the reverse leakage current Ir from flowing into the node between theresistors voltage comparator 123. - The power supply selection/
detection circuit 300 shown inFIG. 3 may include thetransistor 203 shown inFIG. 2 (not shown inFIG. 3 ) between theSchottky diode 122 and themain power supply 102. In this configuration, if the power supply 111 is an AC adapter that is a dedicated line for power supply, it is possible to form a circuit that preferentially supplies the power from the power supply 111 to themain power supply 102 when power is connected to the power supply 111 as described in the first embodiment. The circuit ofFIG. 3 may further include the resistor 202 shown inFIG. 2 . - Although the
voltage comparator 126 detects the presence or absence of an external power supply using a voltage difference after the VF drop due to the PN junction in theSchottky diode 122, it is possible to use a voltage difference between the both ends of the resistor (not shown) between theSchottky diode 122 and themain power supply 102, or a voltage difference between the terminals of the transistor (not shown). It is also possible to use a voltage difference between theSchottky diode 122 and the resistor, a voltage difference between the resistor and the transistor, or a voltage difference between theSchottky diode 122 and the transistor, as described in the first embodiment. - In this configuration, the second embodiment has the same advantage as the first embodiment.
- Further, because the
switch 317 is open-circuited in thepower supply detector 310 related to the power supply 111 which is connected to themain power supply 102, no current flows into thevoltage comparator 316 and theresistor 318. Accordingly, adding thevoltage comparator 316, theresistor 318 and theswitch 317 to thepower supply detector 310 does not cause an increase in power consumption. - A third embodiment of the present invention is described hereinafter with reference to the drawings. In the third embodiment, as in the first embodiment, a power supply selection/detection circuit is described, by way of illustration, as a circuit which includes, as a load, a driver of a hard disk drive or microcomputer of a portable device and which is formed on a semiconductor device such as an LSI.
FIG. 4 shows the configuration of the power supply selection/detection circuit according to the third embodiment. The same circuit elements or operating principles as in the first embodiment are not described herein. - Referring to
FIG. 4 , in a power supply selection/detection circuit 400, the voltage supplied from a power supply 411 or apower supply 421 is applied to aload 401 through amain power supply 402. The power supply selection/detection circuit 400 includes a power supply detector 410 disposed between the power supply 411 and themain power supply 402, and a power supply detector 420 disposed between thepower supply 421 and themain power supply 402. The power supply detector 410 includes aSchottky diode 412, twovoltage comparators resistors switch 417. The power supply detector 410 includes avoltage detector 419, which includes thevoltage comparator 413 and the tworesistors - The power supply detector 420 includes a
Schottky diode 422, twovoltage comparators 423 and 426, and tworesistors switch 427. The power supply detector 420 includes avoltage detector 429, which includes the voltage comparator 423 and theresistors - The power supply selection/
detection circuit 400 supplies power to an external load (not shown) such as a hard disk drive or a microcomputer through theload 401 such as a DC/DC converter, LDO, or a battery charger as described in the first embodiment. The power supply to theload 401 is not limited to the power supplies 411 and 421 and a plurality of power supplies may be added. The power supply selection/detection circuit 400 excluding theSchottky diodes load 401 on a semiconductor device such as LSI, and theresistors - The anode of the
Schottky diode 412 is connected to the power supply 411, and the cathode of theSchottky diode 412 is connected to themain power supply 402. Thevoltage comparator 413 detects the voltage of the power supply 411 to determine the presence or absence of the power supply 411. Thevoltage comparator 413 receives a reference power supply voltage Va1 and a voltage Va2 at a node between theresistors voltage comparator 416 is connected to the power supply 411 on the anode side of theSchottky diode 412, and the other input terminal of thevoltage comparator 416 is connected to themain power supply 402 on the cathode side of theSchottky diode 412 so as to compare a voltage difference between the power supply 411 and themain power supply 402. The output terminal of thevoltage comparator 416 is connected to theswitch 417. One end of theswitch 417 is connected to the power supply 411, and the other end of theswitch 417 is connected to theresistor 414, theresistor 415, and then grounded. Although not shown, theswitch 417 may be placed between theresistor 414 and the input terminal of thevoltage comparator 413. - The anode of the
Schottky diode 422 is connected to thepower supply 421, and the cathode of theSchottky diode 422 is connected to themain power supply 402. The voltage comparator 423 detects the voltage of thepower supply 421 to determine the presence or absence of thepower supply 421. The voltage comparator 423 receives a reference power supply voltage Vb1 and a voltage Vb2 at a node between theresistors power supply 421. The input terminal of thevoltage comparator 426 is connected to thepower supply 421 on the anode side of theSchottky diode 422, and the other input terminal of thevoltage comparator 426 is connected to themain power supply 402 on the cathode side of theSchottky diode 422 so as to compare a voltage difference between thepower supply 421 and themain power supply 402. The output terminal of thevoltage comparator 426 is connected to theswitch 427. One end of theswitch 427 is connected to thepower supply 421, and the other end of theswitch 427 is connected to theresistor 424, theresistor 425, and then grounded. Although not shown, theswitch 427 may be placed between theresistor 424 and the input terminal of the voltage comparator 423. Further, theswitch 427 may be placed between the input terminal of the voltage comparator 423 and theresistor 425, or between theresistor 425 and the ground. - The
switch 417 is short-circuited or open-circuited according to the output from thevoltage comparator 416 based on the comparison between the voltage at the anode of theSchottky diode 412 and the voltage at the cathode of theSchottky diode 412. Specifically, if the voltage of the power supply 411 is lower than the voltage of the main power supply 402 (including when the power supply 411 is not inserted), theswitch 417 is open-circuited. If, on the other hand, the voltage of the power supply 411 is higher than the voltage of themain power supply 402, theswitch 417 is short-circuited. - The
switch 427 is short-circuited or open-circuited according to the output from thevoltage comparator 426 based on the comparison between the voltage at the anode of theSchottky diode 422 and the voltage at the cathode of theSchottky diode 422. Specifically, if the voltage of thepower supply 421 is lower than the voltage of the main power supply 402 (including when thepower supply 421 is not inserted), theswitch 427 is open-circuited. If, on the other hand, the voltage of thepower supply 421 is higher than the voltage of themain power supply 402, theswitch 427 is short-circuited. - The operation of the power supply selection/
detection circuit 400 is described hereinafter with reference toFIG. 4 . In this embodiment, the power supply 411 is described as an AC adapter and thepower supply 421 as an USB connector, for example. The operation of the power supply selection/detection circuit 400 when the voltage supplied from the AC adapter is higher than the voltage supplied from the USB connector, which is when the power supply 411 is higher than thepower supply 421, is described firstly. - When a voltage is supplied to the power supply 411, the voltage of the
main power supply 402 is a voltage that is lower than the voltage of the power supply 411 by the amount of the VF of theSchottky diode 412 due to the PN junction in theSchottky diode 412. The voltage of the power supply 411 is thereby higher than the voltage of themain power supply 402, and theswitch 417 is short-circuited according to the output from thevoltage comparator 416. Accordingly, current flows from the power supply 411 to the ground through theresistors voltage comparator 413 detects that power is being supplied to the power supply 411. - On the other hand, in the power supply detector 420, a voltage lower than that supplied to the power supply 411 is supplied to the
power supply 421. The voltage of thepower supply 421 is thereby lower than the voltage of themain power supply 402, so that theswitch 427 is open-circuited according to the output of thevoltage comparator 426. Accordingly, the voltage Va2 at the node does not increase but stays at the ground level, and thereby the power supply detector 420 does not detect that power is being supplied to thepower supply 421 based on the comparison result in the voltage comparator 423. If theswitch 427 is placed between the voltage comparator 423 and the ground, though not shown, the voltage Vb2 at the node is fixed to about a power supply voltage level while theswitch 427 is open-circuited. Thus, the power supply detector 420 can invert the logic of the voltage comparator 423 so as not to detect that power is being supplied to thepower supply 421. - The operation of the power supply selection/
detection circuit 400 when only the power supply voltage from the AC adapter is connected, which is when only the power supply 411 is connected, is described hereinafter. When a voltage is supplied to the power supply 411, the voltage of themain power supply 402 is a voltage that is lower than the voltage of the power supply 411 by the amount of VF of theSchottky diode 412 due to the PN junction in theSchottky diode 412 in the power supply detector 410. Accordingly, the voltage of the power supply 411 is higher than the voltage of themain power supply 402, and theswitch 417 is short-circuited according to the output from thevoltage comparator 416. Accordingly, current flows from the power supply 411 to the ground through theresistors voltage comparator 413 detects that power is being supplied to the power supply 411 in the power supply detector 410. - On the other hand, in the power supply detector 420, no voltage is supplied to the
power supply 421. The voltage of thepower supply 421 is thereby lower than the voltage of themain power supply 402, so that theswitch 427 is open-circuited according to the output of thevoltage comparator 426. Accordingly, the voltage Va2 at the node does not increase but stays at the ground level, so that the power supply detector 420 does not detect that power is being supplied to thepower supply 421 based on the comparison result in the voltage comparator 423. If theswitch 427 is placed between the voltage comparator 423 and the ground, though not shown, the voltage Va2 at the node is fixed to about a power supply voltage level while theswitch 427 is open-circuited. Thus, the power supply detector 420 can invert the logic of the voltage comparator 423 so as not to detect that power is being supplied to thepower supply 421. - Reverse leakage current Ir from the
main power supply 402 flows into theSchottky diode 422. However, because theswitch 427 is open-circuited, the reverse leakage current Ir does not flows into the node between theresistors - The power supply selection/
detection circuit 400 shown inFIG. 4 may include thetransistor 203 and the resistor 202 shown inFIG. 2 (not shown inFIG. 4 ) between theSchottky diode 422 and themain power supply 402. In this configuration, thevoltage comparator 426 can determine the presence or absence of an external power supply using not only a voltage difference after the VF drop due to the PN junction in theSchottky diode 422, but also a voltage difference between the both ends of the resistor or a voltage difference between the terminals of the transistor. It is also possible to use a voltage difference between theSchottky diode 422 and the resistor, a voltage difference between the resistor and the transistor, or a voltage difference between theSchottky diode 422 and the transistor, as described in the first embodiment. - As described above, it is possible to prevent the reverse leakage current Ir of the
Schottky diode 422 from flowing into theresistors switch 427 which opens and closes according to a voltage difference between the anode and the cathode of theSchottky diode 422. Because the reverse leakage current Ir does not flow into the node between theresistors power supply 421. The resistance of theresistors resistors power supply 421 which is not connected with themain power supply 402. - Similarly, the configuration allows the resistance of the
resistors resistors main power supply 402. As a result, power consumption can be reduced in the power supply detector 410 related to the power supply 411 which is connected with themain power supply 402 as well. - If the resistance of the
resistors resistors resistors - The present invention is particularly suitable for application to portable devices or the like, and may be applied to any devices to which power is supplied from external sources.
- It is apparent that the present invention is not limited to the above embodiment and it may be modified and changed without departing from the scope and spirit of the invention.
Claims (10)
1. A semiconductor device to select a power supply providing a voltage from first and second external power supplies, comprising:
a first node that receives a first voltage from said first external power supply;
a second node that receives a second voltage from said second external power supply;
a third node that receives a third voltage;
a fourth node that receives said third voltage;
an output node coupled to said first node or said second node;
a first switch, a one end of said first switch coupled between said first node and said output node;
a second switch, a one end of said second switch coupled between said second node and said output node;
a first path coupled between said third node and said output node through said first switch; and
a second path coupled between said fourth node and said output node through said second switch,
wherein a control node of said first switch is not connected to said second path.
2. The semiconductor device according to claim 1 , further comprising a switch control circuit that controls said first and second switches,
wherein said first and second switch are controlled by an output voltage of said switch control circuit when said first external power supply or said second external power supply provides a voltage to said output node, complementarily.
3. The semiconductor device according to claim 2 ,
wherein said first switch is turned off when said output voltage indicates that said second external power supply provides a voltage to said output node, and
wherein said second switch is turned off when said output voltage indicates that said first external power supply provides a voltage to said output node.
4. The semiconductor device according to claim 3 ,
wherein said second power supply is a USB (Universal Serial Bus) interface connector, and
wherein a voltage from said first external power supply is larger than a voltage from said second external power supply.
5. The semiconductor device according to claim 4 , further comprising:
a first voltage detector coupled to said first node through said first switch to detect a voltage from said first external power supply; and
a second voltage detector coupled to said second node through said second switch to detect a voltage from said second external power supply.
6. The semiconductor device according to claim 5 ,
wherein said second voltage detector includes first and second voltage-dividing resistors between said second switch and a ground,
7. The semiconductor device according to claim 6 ,
wherein V/Imax>=(R1+R2) is satisfied where a current limit is Imax, a voltage from said second external power supply is V, resistance of said first voltage-dividing resistor is R1, and resistance of said second voltage-dividing resistor is R2.
8. The semiconductor device according to claim 7 , wherein
when a current limit of the USB interface connector in suspend mode is 500 μA and a supply voltage of the USB interface connect is 4.3 to 5.4 V, a total of the resistance of the first and second voltage-dividing resistors is 8.6 KΩ or higher.
9. The semiconductor device according to claim 8 ,
wherein said switch control circuit includes first and second detector, and
wherein the semiconductor device further comprises:
a first resistance element coupled between said first node and said output node; and
a second resistance element coupled between said second node and said output node,
wherein said first detector detects a voltage between both ends of said first resistance element to control said first switch, and
wherein said second detector detects a voltage between both ends of said second resistance element to control said second switch.
10. The semiconductor device according to claim 9 ,
wherein said first and second resistance elements is one of a Schottky diode, a resistor and a transistor.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/654,967 US20130038131A1 (en) | 2006-02-24 | 2012-10-18 | Semiconductor device to select a power supply |
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2006-048547 | 2006-02-24 | ||
JP2006048547A JP4851203B2 (en) | 2006-02-24 | 2006-02-24 | Power supply selection detection circuit and power supply control method |
US11/708,563 US8063514B2 (en) | 2006-02-24 | 2007-02-21 | Power supply selection/detection circuit |
US13/272,711 US8330294B2 (en) | 2006-02-24 | 2011-10-13 | Power supply selection/detection circuit |
US13/654,967 US20130038131A1 (en) | 2006-02-24 | 2012-10-18 | Semiconductor device to select a power supply |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/272,711 Continuation US8330294B2 (en) | 2006-02-24 | 2011-10-13 | Power supply selection/detection circuit |
Publications (1)
Publication Number | Publication Date |
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US20130038131A1 true US20130038131A1 (en) | 2013-02-14 |
Family
ID=38445434
Family Applications (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/708,563 Active 2028-11-01 US8063514B2 (en) | 2006-02-24 | 2007-02-21 | Power supply selection/detection circuit |
US13/272,711 Expired - Fee Related US8330294B2 (en) | 2006-02-24 | 2011-10-13 | Power supply selection/detection circuit |
US13/654,967 Abandoned US20130038131A1 (en) | 2006-02-24 | 2012-10-18 | Semiconductor device to select a power supply |
Family Applications Before (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/708,563 Active 2028-11-01 US8063514B2 (en) | 2006-02-24 | 2007-02-21 | Power supply selection/detection circuit |
US13/272,711 Expired - Fee Related US8330294B2 (en) | 2006-02-24 | 2011-10-13 | Power supply selection/detection circuit |
Country Status (3)
Country | Link |
---|---|
US (3) | US8063514B2 (en) |
JP (1) | JP4851203B2 (en) |
CN (1) | CN101025654B (en) |
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Also Published As
Publication number | Publication date |
---|---|
US8330294B2 (en) | 2012-12-11 |
JP2007226638A (en) | 2007-09-06 |
CN101025654A (en) | 2007-08-29 |
US20070204178A1 (en) | 2007-08-30 |
US8063514B2 (en) | 2011-11-22 |
JP4851203B2 (en) | 2012-01-11 |
US20120032726A1 (en) | 2012-02-09 |
CN101025654B (en) | 2010-06-16 |
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