US20230163617A1 - Reducing corruption of communication in a wireless power transmission system - Google Patents
Reducing corruption of communication in a wireless power transmission system Download PDFInfo
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- US20230163617A1 US20230163617A1 US18/095,956 US202318095956A US2023163617A1 US 20230163617 A1 US20230163617 A1 US 20230163617A1 US 202318095956 A US202318095956 A US 202318095956A US 2023163617 A1 US2023163617 A1 US 2023163617A1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/0071—Regulation of charging or discharging current or voltage with a programmable schedule
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
- H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
- H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
- H02J7/00714—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters in response to battery charging or discharging current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
- H02J7/007182—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters in response to battery voltage
Definitions
- Inductive coupling couples magnetic energy from one coil to another coil.
- Inductive coupling may be used in transformers to change a voltage on a primary coil (also called a winding) to a higher or lower voltage on a secondary coil.
- a primary coil also called a winding
- high voltage power lines use transformers to “step down” high voltages on power lines to lower voltages (e.g. 120 volts) that may be used in homes.
- Transformers may be used to isolate one electrical system from another electrical system.
- the transfer of energy can be more efficient if a magnetic medium such as iron is used. However, energy may be transferred through a medium such as air from one coil to another coil. Because inductive coupling does not need an electrical conductor to transfer energy from one coil to another coil, batteries in electronic devices may be charged without requiring an electrical cord to be attached to the electronic device. For example, many electric toothbrushes use inductive coupling to recharge batteries in the electrical toothbrushes. These electric toothbrushes are charged by simply placing them on a stand that contains a source of magnetic energy.
- Inductive coupling may be used to transfer electrical power as in the case where high voltage transformers transfer power from high voltage power lines to homes.
- inductive coupling may be used for communication.
- a transformer may be used to transfer an analog signal (e.g. an audio signal) from an amplifier to a loudspeaker in order to produce sound.
- digital signals may be transmitted from one coil to another coil in order to facilitate communication.
- Inductive coupling may be used to transfer power and transmit information concurrently.
- backscatter modulation is a method of communicating in an inductively coupled system where power is transferred from the power transmitter to the power receiver and information is communicated from the power receiver back to the power transmitter.
- inductive coupling is used to transfer power and transmit information concurrently, the transfer of power may corrupt the transmission of information.
- the charging of a battery can create digital pulses that are transmitted from a receiver to the transmitter corrupting data that is communicated from the receiver to the transmitter.
- FIG. 1 is a schematic diagram of an embodiment of a wireless power transmission system.
- FIG. 2 is a schematic diagram of an embodiment of a wireless power transmission system with a charge control circuit.
- FIG. 3 is a schematic diagram of a first embodiment of a charge control circuit.
- FIG. 4 is a schematic diagram of a second embodiment of a charge control circuit.
- FIG. 5 is a plot of an embodiment of a charging profile for a lithium-ion battery as a function of time and current.
- FIG. 6 is a flow chart of an embodiment of a method for reducing corruption of communication in a wireless power transmission system.
- a primary coil in a transmitter generates a magnetic field which is magnetically coupled to a secondary coil of a receiver.
- the magnetic field coupled from the primary coil to the secondary coil induces an AC (alternating current) voltage on the secondary coil, which is then rectified to generate a DC (direct current) voltage at the rectifier node.
- This DC rectifier voltage will cause a current to flow into an output load.
- a charge control circuit placed between the rectifier circuit and the load limits the change in current to the load.
- the current supplied to the load may change significantly.
- the current supplied to the load may change significantly due to the dynamic load requirements associated with power transmission in a cellular phone.
- Change in the current supplied to the load induces a change in current on the secondary coil in the receiver.
- Change in current on the secondary coil induces a signal to be magnetically coupled from the receiver to the transmitter.
- the signal magnetically coupled from the receiver to the transmitter may corrupt communication being sent concurrently from the receiver to the transmitter.
- the intended communication from the receiver to the transmitter may be corrupted by a signal induced on the secondary coil by a change in current to the load being charged.
- a charge control circuit is placed between a rectifier and a load. Because the change in current to the load is reduced when the charge control circuit is placed between the rectifier and the load, corruption of communication from the receiver to the transmitter is reduced. The function of the charge control circuit within a wireless power transmission system will be discussed later in more detail.
- Power may be transferred from a transmitter to a receiver concurrently with communication being sent from the receiver to the transmitter. Because power is being transferred concurrently with communication being sent, power induced in the receiver can create a signal that is sent from the receiver to the transmitter that may corrupt the intended communication sent from the receiver to the transmitter.
- FIG. 1 illustrates how communication may be corrupted in a wireless power transmission system 100 that uses backscatter modulation.
- a control circuit 102 controls a driver circuit 104 through electrical connections 112 and 114 .
- the driver circuit 104 drives a current I 1 through the resonant circuit 106 .
- the resonant circuit is an LC (inductor-capacitor) circuit containing a capacitor C 1 and a coil L 1 in series.
- Other resonant circuits may be used such as an LLC (inductor-inductor-capacitor) circuit.
- the current I 1 is approximately sinusoidal.
- Rectifier circuit 108 contains a center-tapped coil, two diodes D 1 and D 2 , and a capacitor C 2 .
- the rectifier circuit 108 in this example is a full-wave center-tapped rectification circuit; however, other types of rectification may be used such as full-wave non-center-tapped rectification or half-wave rectification.
- the rectifier circuit 108 provides a voltage on node 124 .
- the voltage on node 124 causes a current I 3 to charge the load 110 .
- the load 110 for example, may be a battery, a battery charger or a power supply.
- the current I 3 that charges the load 110 also causes a change in current I 4 in the center-tapped coil L 2 .
- the change in current I 4 in the center-tapped coil L 2 induces a change in current I 5 in the coil L 1 .
- the change in current I 5 in the coil L 1 may corrupt communication from the receiver 130 to the transmitter 128 .
- Modulating the voltage on node COMM creates communication from the receiver 130 to the transmitter 128 by backscatter modulation.
- the change in current I 5 due to the change in current I 3 into the load 110 may corrupt the communication sent by the modulation of node COMM.
- the corruption of communication from the receiver 130 to the transmitter 128 may be reduced by limiting the change in current I 3 charging the load 110 .
- the change in current I 3 for charging the load 110 is limited by inserting a charge control circuit between the rectifier circuit 108 and the load 110 .
- FIG. 2 is a schematic drawing of an embodiment of a wireless power transmission system 200 that uses backscatter modulation wherein corruption of communication is limited.
- a control circuit 102 controls a driver circuit 104 through electrical connections 208 and 210 .
- the driver circuit 104 drives a current I 1 through the resonant circuit 106 .
- the driver circuit 104 in this example, contains a PFET (p-type field-effect transistor) PFET 1 and an NFET (n-type field-effect transistor) NFET 1 ; however, other transistors may be used.
- An input 208 to the driver circuit 104 is connected to the gate of PFET 1 and an input 210 of the driver circuit 104 is connected to the gate of NFET 1 .
- the source of PFET 1 is connected to VDD and the source of NFET is connected to ground.
- the drains of PFET 1 and NFET 2 are connected to the output 212 of the driver circuit 104 .
- the resonant circuit 106 is an LC (inductor-capacitor) circuit containing a capacitor C 1 and a coil L 1 in series.
- Other resonant circuits may be used such as an LLC (inductor-inductor-capacitor) circuit.
- the current I 1 is approximately sinusoidal.
- an approximately sinusoidal current I 2 is induced on coil L 2 in the rectifier circuit 108 .
- Rectifier circuit 108 contains a center-tapped coil L 2 , two diodes D 1 and D 2 , and a capacitor C 2 .
- the rectifier circuit 108 in this example, is a full-wave center-tapped rectification circuit; however, other types of rectification may be used such as full-wave non-center-tapped rectification or half-wave rectification.
- the anode of diode D 1 is connected to a terminal of center-tapped coil L 2 and the anode of diode D 2 is connected to another terminal of center-tapped coil L 2 .
- the center of center-tapped coil L 2 is grounded.
- the cathode of diode D 1 , the cathode of diode D 2 and a terminal of C 2 are connected to the output of the rectifier circuit 108 at node 218 .
- the rectifier circuit 108 provides a voltage on node 218 .
- the voltage on node 218 causes a current I 3 to flow.
- the charge control circuit 206 limits the change in current I 3 .
- the change in current I 3 is limited, the change in current I 4 in the center-tapped coil L 2 is substantially reduced. Reducing the change in current I 4 in the center-tapped coil L 2 also reduces the change in current I 5 in the coil L 1 . Because the change in current I 5 in the coil L 1 is reduced, the probability of corruption of communication from the receiver 202 to the transmitter 128 is also reduced. Modulating the voltage on node COMM of the communication switch 204 , creates communication from the receiver 202 to the transmitter 128 by backscatter modulation.
- a communication switch 204 includes resistor R 1 and NFET NFET 2 in series. When the change in current I 3 is reduced by the charge control circuit 206 , the communication created by the communication switch 204 has a lower probability of being corrupted.
- the charge control circuit 206 measures current I 3 being supplied to the load 110 . After measuring the current I 3 , the control circuit 206 sets a current regulation threshold below the present value of current I 3 . Setting the current regulation threshold below the present value of current I 3 forces the charge control circuit 206 to operate in current limit. Operating in current limit reduces the change in current I 3 . As a result, the probability of communication being corrupted to the transmitter 128 is reduced.
- the load 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply.
- the charge control circuit 206 measures current I 3 being supplied to the load 110 . After measuring the current I 3 , the control circuit 206 sets a current regulation threshold slightly above the present value of current I 3 . Typically, a 200 ma current pulse is used for communication. Therefore, if the change in current increases by 100 ma or less, communication will not be corrupted. However, if the current pulse used for communication is increased, the current regulation threshold may also be raised without corrupting communication.
- the load 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply.
- the charge control circuit 206 measures current I 3 being supplied to the load 110 .
- the current regulation threshold is set at 200 ma.
- One reason for setting the current regulation limit to 200 ma when the measured current I 3 is 200 ma or less is to protect against the wireless power transmission system shutting down based on an under-voltage or an under-current condition.
- the load 110 that is charged may be a battery, a battery charger or a power supply.
- the load is not limited to a battery, a battery charger or a power supply.
- a fourth embodiment of the charge control circuit 206 when there is no communication between the receiver 202 and the transmitter 128 , no current regulation threshold is set. Instead, the change in current I 3 may be increased to the load 110 . A full charge current may be used during this condition because there is no communication between the receiver 202 and the transmitter 128 . Because there is no communication between the receiver 202 and the transmitter 128 , there is no communication to corrupt.
- the load 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply.
- FIG. 3 is a schematic drawing of an embodiment of a charge control circuit 300 .
- the charge control circuit 300 in FIG. 3 acts as a current limiter whose threshold tracks the present value of current I 3 through device NFET 3 .
- the element 322 acts as a current sensor 322 .
- the current sensor 322 allows charge current I 3 to pass from the input 326 of the charge control circuit 300 to node 308 substantially unchanged.
- An output from current sensor 322 is connected to node 324 .
- the current I 6 drawn through resistor R 2 is a scaled version of the current I 3 at node 308 .
- the current I 6 is approximately equal to I 3 /k, where the value of k is typically between 100 and 1000. Current I 6 flows through the resistor R 2 creating a voltage at node 324 that is proportional to the current I 3 .
- op-amp 306 and associated resistors R 3 and R 4 create a non-inverting gain function that amplifies the voltage at node 324 by a factor, typically 1.05. However, other factors are also possible.
- the resistor R 5 and the capacitor C 3 form a low-pass filter that acts to hold the amplified voltage at node 316 .
- the charge pump 302 acts as current source that will turn on the gate of NFET 3 and provide a bias voltage for the gate of NFET 3 .
- An embodiment of the current limit function of the charge control circuit 300 operates as follows: when the load current I 7 pulled from node 310 changes quickly (quickly in this embodiment means approximately 10 times faster than the time constant T 4 , where T 4 equals (R 5 ⁇ C 3 ) seconds), then the voltage at node 324 will increase proportionally to the change in load current I 7 while the voltage at node 316 does not substantially change at the same time. Therefore, a negative differential voltage is created at the input of op-amp 304 that will cause current to flow into op-amp 304 . The current flowing into op-amp 304 will lower the voltage on the gate 312 of NFET 3 and inhibit the change in load current I 7 .
- a negative feedback loop formed in the charge control circuit 300 limits the rate at which the load current I 7 can change by the time constant T 4 .
- the time constant T 4 can be changed by varying the value of the external capacitor C 3 .
- the circuit 300 will improve communication by shielding fast current changes from a transmitter.
- charge control circuit 300 Other embodiments of charge control circuit 300 are also possible. For example, an enabling function may be added that would turn on charge control circuit 300 during the communication period and then turn it off when communication is complete. In this way, the charger can quickly deliver its full current when communication is not active.
- the charge control circuit 300 sets a tracking current limit which is used during voltage regulation.
- another amplifier (not shown) may be added to the charge control circuit 300 to set a maximum current limit independent of the voltage on capacitor C 3 .
- the charge current into node 308 will not run away because the tracking current limit will be active for relatively short periods of time when power is applied.
- FIG. 4 is a schematic drawing of an embodiment of a charge control circuit 400 .
- the charge control circuit 400 in FIG. 4 acts as a current limiter whose threshold tracks the present value of current I 3 through device NFET 4 .
- the element 322 acts as a current sensor 322 .
- the current sensor 322 allows charge current I 3 to pass from the input 420 of the charge control circuit 400 to node 408 substantially unchanged.
- An output from current sensor 322 is connected to node 422 .
- the current I 6 drawn through resistor R 6 and R 7 is a scaled version of the current I 3 at node 408 .
- the current I 6 is approximately equal to I 3 /k, where the value of k is typically between 100 and 1000.
- Current I 6 flows through the resistors R 6 and R 7 creating voltages at nodes 422 and 410 that are proportional to the current I 3 .
- the input of the charge control circuit 400 is connected to node 420 .
- a voltage proportional to the change in current I 3 on node 410 is presented to a first input of the op-amp 406 .
- a voltage divider is created by resistor R 6 in series with resistor R 7 .
- the value of R 6 is equal to (0.05)*R 7 . Because the value of R 6 is equal to (0.05)*R 7 , the voltage on node 410 is approximately (0.95) times the voltage on node 422 .
- Node 408 is connected to the current sensor 322 and the drain of NFET NFET 4 .
- Node 422 is connected to the input of ADC 402 and resistor R 6 .
- the output 416 of the ADC 402 is connected to the input of the DAC (digital-to-analog converter) 404 .
- An 8-bit bus is used in this example; however, the output 416 of the ADC 402 may be any size bus.
- the bus may be a 16 bit bus.
- the DAC 404 converts the digital signal from the output 416 of the ADC 402 to an analog signal on node 412 .
- the voltage on node 412 is presented to a second input of the op-amp 406 .
- the op-amp 406 compares the voltages on nodes 412 and 410 . When the voltage on node 412 is higher than the voltage on node 410 , the op-amp 406 increases the voltage on node 414 . The node 414 is connected to the gate of NFET 4 . When the voltage on node 412 is lower than the voltage on node 410 , the op-amp 406 decreases the voltage on node 414 . Changing the voltage on node 412 based on the current I 6 drawn through resistors R 6 and R 7 regulates the current drawn on node 408 . By regulating the current through NFET 4 , the current drawn on node 408 is substantially constant. Keeping the current approximately constant on node 408 reduces corruption in communication from the receiver 202 to the transmitter 128 .
- the use of the ADC 402 and the DAC 404 between nodes 408 and 412 allows for more precise control of the tracking current limit.
- the charge control circuit 400 does not need an external capacitor as in the embodiment of the charge control circuit 300 shown in FIG. 3 .
- An embodiment of the invention may be used to charge, for example, lithium-ion batteries.
- a typical charging profile for lithium-ion batteries is shown in FIG. 5 .
- the charging of a lithium-ion battery begins with a preconditioning period T 1 .
- the charge current CC is relatively low and held at a constant value. Because the charge current CC is a constant value, the charge voltage CV increases linearly until a minimum charge voltage is reached.
- the precondition phase T 1 ends and the current regulation phase or “fast charge” phase T 2 begins.
- the charge current CC is increased and held at a constant value. Because the charge current CC is a constant value, the charge voltage CV increases linearly until the lithium-ion battery is nearly charged.
- the current regulation phase T 2 ends and the voltage regulation phase T 3 begins.
- the charge current CC tapers until the charge is complete.
- the charge current CC is no longer constant. Because the charge current CC is changing during the voltage regulation phase T 3 , a change in current will also occur in a coil L 2 of a receiver 202 . When a change in current occurs in the coil L 2 , communication sent from the receiver 202 to the transmitter 128 may be corrupted.
- An embodiment of the invention may be used to lower the probability of communication being corrupted during the voltage regulation phase T 3 of charging lithium-ion batteries in a wireless power transmission system.
- the voltage regulation phase T 3 of charging lithium-ion batteries is shown in FIG. 5 where the charging current CC is reduced over a time period.
- the use of a charge control circuit, for example the charge control circuit 300 shown in FIG. 3 during the voltage regulation phase T 3 of charging lithium-ion batteries, will reduce the change in charging current CC. Because the change in charging current CC is reduced, the probability of corruption of communication from the receiver 202 to the transmitter 128 will be reduced as well.
- FIG. 6 is a flow diagram of an embodiment of a method of reducing corruption of communication in a wireless power transmission system 200 .
- step 602 power is transmitted from a primary coil L 1 to a secondary coil L 2 by induction.
- step 604 the voltage induced on the secondary coil L 2 by the transmission of power from the primary coil L 1 to the secondary coil L 2 is rectified.
- step 606 the change in current supplied to a load 110 while power is induced on the secondary coil L 2 is limited. Because the change in current is limited, corruption of communication from a receiver 202 to a transmitter 128 in a wireless transmission system 200 is reduced.
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- Charge And Discharge Circuits For Batteries Or The Like (AREA)
Abstract
An embodiment of the invention provides a method for reducing data corruption in a wireless power transmission system. Power is transmitted from a primary coil to a secondary coil by induction. The voltage induced on the secondary coil by induction is rectified. The change in current supplied to a load configured to be coupled to the wireless power transmission system is limited.
Description
- This application is a continuation of prior application Ser. No. 16/540,964, filed Aug. 14, 2019, currently pending;
- Which was a divisional of prior application Ser. No. 15/959,443, filed Apr. 23, 2018, now abandoned;
- Which was a continuation of prior application Ser. No. 15/131,732, filed Apr. 18, 2016, now U.S. Pat. No. 9,954,402, granted Apr. 24, 2018;
- Which was a continuation of prior application Ser. No. 12/838,298, filed Jul. 16, 2010, now U.S. Pat. No. 9,318,897, granted Apr. 19, 2016;
- Which claims priority to U.S. Provisional Application No. 61/227,332, filed Jul. 21, 2009, the entirety of which are incorporated by reference herein.
- Inductive coupling, often called magnetic coupling, couples magnetic energy from one coil to another coil. Inductive coupling may be used in transformers to change a voltage on a primary coil (also called a winding) to a higher or lower voltage on a secondary coil. For example, high voltage power lines use transformers to “step down” high voltages on power lines to lower voltages (e.g. 120 volts) that may be used in homes. Transformers may be used to isolate one electrical system from another electrical system.
- The transfer of energy can be more efficient if a magnetic medium such as iron is used. However, energy may be transferred through a medium such as air from one coil to another coil. Because inductive coupling does not need an electrical conductor to transfer energy from one coil to another coil, batteries in electronic devices may be charged without requiring an electrical cord to be attached to the electronic device. For example, many electric toothbrushes use inductive coupling to recharge batteries in the electrical toothbrushes. These electric toothbrushes are charged by simply placing them on a stand that contains a source of magnetic energy.
- Inductive coupling may be used to transfer electrical power as in the case where high voltage transformers transfer power from high voltage power lines to homes. In addition to transferring power, inductive coupling may be used for communication. For example, a transformer may be used to transfer an analog signal (e.g. an audio signal) from an amplifier to a loudspeaker in order to produce sound. In addition, digital signals may be transmitted from one coil to another coil in order to facilitate communication.
- Inductive coupling may be used to transfer power and transmit information concurrently. For example, backscatter modulation is a method of communicating in an inductively coupled system where power is transferred from the power transmitter to the power receiver and information is communicated from the power receiver back to the power transmitter. When inductive coupling is used to transfer power and transmit information concurrently, the transfer of power may corrupt the transmission of information. For example, in a system using backscatter modulation, the charging of a battery can create digital pulses that are transmitted from a receiver to the transmitter corrupting data that is communicated from the receiver to the transmitter.
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FIG. 1 is a schematic diagram of an embodiment of a wireless power transmission system. -
FIG. 2 is a schematic diagram of an embodiment of a wireless power transmission system with a charge control circuit. -
FIG. 3 is a schematic diagram of a first embodiment of a charge control circuit. -
FIG. 4 is a schematic diagram of a second embodiment of a charge control circuit. -
FIG. 5 is a plot of an embodiment of a charging profile for a lithium-ion battery as a function of time and current. -
FIG. 6 is a flow chart of an embodiment of a method for reducing corruption of communication in a wireless power transmission system. - The drawings and description, in general, disclose embodiments of a method and apparatus for reducing corruption of communication in a wireless power transmission system. In summary, a primary coil in a transmitter generates a magnetic field which is magnetically coupled to a secondary coil of a receiver. The magnetic field coupled from the primary coil to the secondary coil induces an AC (alternating current) voltage on the secondary coil, which is then rectified to generate a DC (direct current) voltage at the rectifier node. This DC rectifier voltage will cause a current to flow into an output load. A charge control circuit placed between the rectifier circuit and the load limits the change in current to the load.
- When a charge control circuit is not placed between the rectifier circuit and the load, the current supplied to the load may change significantly. The current supplied to the load may change significantly due to the dynamic load requirements associated with power transmission in a cellular phone. Change in the current supplied to the load induces a change in current on the secondary coil in the receiver. Change in current on the secondary coil induces a signal to be magnetically coupled from the receiver to the transmitter. The signal magnetically coupled from the receiver to the transmitter may corrupt communication being sent concurrently from the receiver to the transmitter.
- For example, in a wireless power transmission system that uses backscatter modulation, the intended communication from the receiver to the transmitter may be corrupted by a signal induced on the secondary coil by a change in current to the load being charged. To reduce corruption of communication while a load is being charged, a charge control circuit is placed between a rectifier and a load. Because the change in current to the load is reduced when the charge control circuit is placed between the rectifier and the load, corruption of communication from the receiver to the transmitter is reduced. The function of the charge control circuit within a wireless power transmission system will be discussed later in more detail.
- Power may be transferred from a transmitter to a receiver concurrently with communication being sent from the receiver to the transmitter. Because power is being transferred concurrently with communication being sent, power induced in the receiver can create a signal that is sent from the receiver to the transmitter that may corrupt the intended communication sent from the receiver to the transmitter.
FIG. 1 illustrates how communication may be corrupted in a wirelesspower transmission system 100 that uses backscatter modulation. - A
control circuit 102 controls adriver circuit 104 throughelectrical connections driver circuit 104 drives a current I1 through theresonant circuit 106. In this example, the resonant circuit is an LC (inductor-capacitor) circuit containing a capacitor C1 and a coil L1 in series. Other resonant circuits may be used such as an LLC (inductor-inductor-capacitor) circuit. In this example, the current I1 is approximately sinusoidal. - When current I1 is drawn through coil L1, an approximately sinusoidal current I2 is induced on coil L2 in the
rectifier circuit 108.Rectifier circuit 108 contains a center-tapped coil, two diodes D1 and D2, and a capacitor C2. Therectifier circuit 108 in this example is a full-wave center-tapped rectification circuit; however, other types of rectification may be used such as full-wave non-center-tapped rectification or half-wave rectification. Therectifier circuit 108 provides a voltage onnode 124. The voltage onnode 124 causes a current I3 to charge theload 110. Theload 110, for example, may be a battery, a battery charger or a power supply. - In this example, the current I3 that charges the
load 110 also causes a change in current I4 in the center-tapped coil L2. The change in current I4 in the center-tapped coil L2 induces a change in current I5 in the coil L1. The change in current I5 in the coil L1 may corrupt communication from thereceiver 130 to thetransmitter 128. Modulating the voltage on node COMM, creates communication from thereceiver 130 to thetransmitter 128 by backscatter modulation. The change in current I5 due to the change in current I3 into theload 110 may corrupt the communication sent by the modulation of node COMM. - In an embodiment of the invention, the corruption of communication from the
receiver 130 to thetransmitter 128 may be reduced by limiting the change in current I3 charging theload 110. In an embodiment of the invention, the change in current I3 for charging theload 110 is limited by inserting a charge control circuit between therectifier circuit 108 and theload 110. Several embodiments of the charge control circuit and how they are used in a wireless power transmission system that uses backscatter modulation will now be discussed in order to best explain the applicable principles and their practical application. -
FIG. 2 is a schematic drawing of an embodiment of a wirelesspower transmission system 200 that uses backscatter modulation wherein corruption of communication is limited. Acontrol circuit 102 controls adriver circuit 104 throughelectrical connections driver circuit 104 drives a current I1 through theresonant circuit 106. Thedriver circuit 104, in this example, contains a PFET (p-type field-effect transistor) PFET1 and an NFET (n-type field-effect transistor) NFET1; however, other transistors may be used. Aninput 208 to thedriver circuit 104 is connected to the gate of PFET1 and aninput 210 of thedriver circuit 104 is connected to the gate of NFET1. The source of PFET1 is connected to VDD and the source of NFET is connected to ground. The drains of PFET1 and NFET2 are connected to theoutput 212 of thedriver circuit 104. - In this example, the
resonant circuit 106 is an LC (inductor-capacitor) circuit containing a capacitor C1 and a coil L1 in series. Other resonant circuits may be used such as an LLC (inductor-inductor-capacitor) circuit. In this example, the current I1 is approximately sinusoidal. When current I1 is drawn through coil L1, an approximately sinusoidal current I2 is induced on coil L2 in therectifier circuit 108. -
Rectifier circuit 108 contains a center-tapped coil L2, two diodes D1 and D2, and a capacitor C2. Therectifier circuit 108, in this example, is a full-wave center-tapped rectification circuit; however, other types of rectification may be used such as full-wave non-center-tapped rectification or half-wave rectification. The anode of diode D1 is connected to a terminal of center-tapped coil L2 and the anode of diode D2 is connected to another terminal of center-tapped coil L2. The center of center-tapped coil L2 is grounded. The cathode of diode D1, the cathode of diode D2 and a terminal of C2 are connected to the output of therectifier circuit 108 atnode 218. Therectifier circuit 108 provides a voltage onnode 218. The voltage onnode 218 causes a current I3 to flow. In an embodiment of the invention, thecharge control circuit 206 limits the change in current I3. - Because the change in current I3 is limited, the change in current I4 in the center-tapped coil L2 is substantially reduced. Reducing the change in current I4 in the center-tapped coil L2 also reduces the change in current I5 in the coil L1. Because the change in current I5 in the coil L1 is reduced, the probability of corruption of communication from the
receiver 202 to thetransmitter 128 is also reduced. Modulating the voltage on node COMM of thecommunication switch 204, creates communication from thereceiver 202 to thetransmitter 128 by backscatter modulation. - A
communication switch 204 includes resistor R1 and NFET NFET2 in series. When the change in current I3 is reduced by thecharge control circuit 206, the communication created by thecommunication switch 204 has a lower probability of being corrupted. - In a first embodiment of the
charge control circuit 206, thecharge control circuit 206 measures current I3 being supplied to theload 110. After measuring the current I3, thecontrol circuit 206 sets a current regulation threshold below the present value of current I3. Setting the current regulation threshold below the present value of current I3 forces thecharge control circuit 206 to operate in current limit. Operating in current limit reduces the change in current I3. As a result, the probability of communication being corrupted to thetransmitter 128 is reduced. In this first embodiment of acharge control circuit 206, theload 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply. - In a second embodiment of the
charge control circuit 206, thecharge control circuit 206 measures current I3 being supplied to theload 110. After measuring the current I3, thecontrol circuit 206 sets a current regulation threshold slightly above the present value of current I3. Typically, a 200 ma current pulse is used for communication. Therefore, if the change in current increases by 100 ma or less, communication will not be corrupted. However, if the current pulse used for communication is increased, the current regulation threshold may also be raised without corrupting communication. In this second embodiment of acharge control circuit 206, theload 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply. - In a third embodiment of the
charge control circuit 206, thecharge control circuit 206 measures current I3 being supplied to theload 110. When the measured current is 200 ma or less, the current regulation threshold is set at 200 ma. One reason for setting the current regulation limit to 200 ma when the measured current I3 is 200 ma or less is to protect against the wireless power transmission system shutting down based on an under-voltage or an under-current condition. In this third embodiment of acharge control circuit 206, theload 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply. - In a fourth embodiment of the
charge control circuit 206, when there is no communication between thereceiver 202 and thetransmitter 128, no current regulation threshold is set. Instead, the change in current I3 may be increased to theload 110. A full charge current may be used during this condition because there is no communication between thereceiver 202 and thetransmitter 128. Because there is no communication between thereceiver 202 and thetransmitter 128, there is no communication to corrupt. In this fourth embodiment of acharge control circuit 206, theload 110 that is charged may be a battery, a battery charger or a power supply. However, the load is not limited to a battery, a battery charger or a power supply. -
FIG. 3 is a schematic drawing of an embodiment of acharge control circuit 300. Thecharge control circuit 300 inFIG. 3 acts as a current limiter whose threshold tracks the present value of current I3 through device NFET3. In thischarge control circuit 300, theelement 322 acts as acurrent sensor 322. Thecurrent sensor 322 allows charge current I3 to pass from theinput 326 of thecharge control circuit 300 tonode 308 substantially unchanged. An output fromcurrent sensor 322 is connected tonode 324. The current I6 drawn through resistor R2 is a scaled version of the current I3 atnode 308. The current I6 is approximately equal to I3/k, where the value of k is typically between 100 and 1000. Current I6 flows through the resistor R2 creating a voltage atnode 324 that is proportional to the current I3. - In
FIG. 3 , op-amp 306 and associated resistors R3 and R4 create a non-inverting gain function that amplifies the voltage atnode 324 by a factor, typically 1.05. However, other factors are also possible. The resistor R5 and the capacitor C3 form a low-pass filter that acts to hold the amplified voltage atnode 316. Thecharge pump 302 acts as current source that will turn on the gate of NFET3 and provide a bias voltage for the gate of NFET3. - An embodiment of the current limit function of the
charge control circuit 300 operates as follows: when the load current I7 pulled fromnode 310 changes quickly (quickly in this embodiment means approximately 10 times faster than the time constant T4, where T4 equals (R5×C3) seconds), then the voltage atnode 324 will increase proportionally to the change in load current I7 while the voltage atnode 316 does not substantially change at the same time. Therefore, a negative differential voltage is created at the input of op-amp 304 that will cause current to flow into op-amp 304. The current flowing into op-amp 304 will lower the voltage on thegate 312 of NFET3 and inhibit the change in load current I7. - A negative feedback loop formed in the
charge control circuit 300 limits the rate at which the load current I7 can change by the time constant T4. The time constant T4 can be changed by varying the value of the external capacitor C3. When the time constant T4 is slower than the communication time, thecircuit 300 will improve communication by shielding fast current changes from a transmitter. - Other embodiments of
charge control circuit 300 are also possible. For example, an enabling function may be added that would turn oncharge control circuit 300 during the communication period and then turn it off when communication is complete. In this way, the charger can quickly deliver its full current when communication is not active. - In the embodiment of the
charge control circuit 300 shown inFIG. 3 , thecharge control circuit 300 sets a tracking current limit which is used during voltage regulation. However, another amplifier (not shown) may be added to thecharge control circuit 300 to set a maximum current limit independent of the voltage on capacitor C3. The charge current intonode 308 will not run away because the tracking current limit will be active for relatively short periods of time when power is applied. -
FIG. 4 is a schematic drawing of an embodiment of acharge control circuit 400. Thecharge control circuit 400 inFIG. 4 acts as a current limiter whose threshold tracks the present value of current I3 through device NFET4. In thischarge control circuit 400, theelement 322 acts as acurrent sensor 322. Thecurrent sensor 322 allows charge current I3 to pass from theinput 420 of thecharge control circuit 400 tonode 408 substantially unchanged. An output fromcurrent sensor 322 is connected tonode 422. The current I6 drawn through resistor R6 and R7 is a scaled version of the current I3 atnode 408. The current I6 is approximately equal to I3/k, where the value of k is typically between 100 and 1000. Current I6 flows through the resistors R6 and R7 creating voltages atnodes - In this embodiment, the input of the
charge control circuit 400 is connected tonode 420. A voltage proportional to the change in current I3 onnode 410 is presented to a first input of the op-amp 406. In this embodiment, a voltage divider is created by resistor R6 in series with resistor R7. In this example, the value of R6 is equal to (0.05)*R7. Because the value of R6 is equal to (0.05)*R7, the voltage onnode 410 is approximately (0.95) times the voltage onnode 422. -
Node 408 is connected to thecurrent sensor 322 and the drain of NFET NFET4.Node 422 is connected to the input ofADC 402 and resistor R6. Theoutput 416 of theADC 402, an 8-bit bus, is connected to the input of the DAC (digital-to-analog converter) 404. An 8-bit bus is used in this example; however, theoutput 416 of theADC 402 may be any size bus. For example, the bus may be a 16 bit bus. TheDAC 404 converts the digital signal from theoutput 416 of theADC 402 to an analog signal onnode 412. The voltage onnode 412 is presented to a second input of the op-amp 406. - The op-
amp 406 compares the voltages onnodes node 412 is higher than the voltage onnode 410, the op-amp 406 increases the voltage onnode 414. Thenode 414 is connected to the gate of NFET4. When the voltage onnode 412 is lower than the voltage onnode 410, the op-amp 406 decreases the voltage onnode 414. Changing the voltage onnode 412 based on the current I6 drawn through resistors R6 and R7 regulates the current drawn onnode 408. By regulating the current through NFET4, the current drawn onnode 408 is substantially constant. Keeping the current approximately constant onnode 408 reduces corruption in communication from thereceiver 202 to thetransmitter 128. - The use of the
ADC 402 and theDAC 404 betweennodes charge control circuit 400 does not need an external capacitor as in the embodiment of thecharge control circuit 300 shown inFIG. 3 . - An embodiment of the invention may be used to charge, for example, lithium-ion batteries. A typical charging profile for lithium-ion batteries is shown in
FIG. 5 . The charging of a lithium-ion battery begins with a preconditioning period T1. During this time, the charge current CC is relatively low and held at a constant value. Because the charge current CC is a constant value, the charge voltage CV increases linearly until a minimum charge voltage is reached. - When the minimum charge voltage is reached, the precondition phase T1 ends and the current regulation phase or “fast charge” phase T2 begins. During the current regulation phase T2, the charge current CC is increased and held at a constant value. Because the charge current CC is a constant value, the charge voltage CV increases linearly until the lithium-ion battery is nearly charged.
- When the lithium-ion battery is nearly charged, the current regulation phase T2 ends and the voltage regulation phase T3 begins. During the voltage regulation phase T3, the charge current CC tapers until the charge is complete. During the voltage regulation phase T3, the charge current CC is no longer constant. Because the charge current CC is changing during the voltage regulation phase T3, a change in current will also occur in a coil L2 of a
receiver 202. When a change in current occurs in the coil L2, communication sent from thereceiver 202 to thetransmitter 128 may be corrupted. - An embodiment of the invention may be used to lower the probability of communication being corrupted during the voltage regulation phase T3 of charging lithium-ion batteries in a wireless power transmission system. The voltage regulation phase T3 of charging lithium-ion batteries is shown in
FIG. 5 where the charging current CC is reduced over a time period. The use of a charge control circuit, for example thecharge control circuit 300 shown inFIG. 3 , during the voltage regulation phase T3 of charging lithium-ion batteries, will reduce the change in charging current CC. Because the change in charging current CC is reduced, the probability of corruption of communication from thereceiver 202 to thetransmitter 128 will be reduced as well. -
FIG. 6 is a flow diagram of an embodiment of a method of reducing corruption of communication in a wirelesspower transmission system 200. Instep 602, power is transmitted from a primary coil L1 to a secondary coil L2 by induction. Instep 604, the voltage induced on the secondary coil L2 by the transmission of power from the primary coil L1 to the secondary coil L2 is rectified. Instep 606, the change in current supplied to aload 110 while power is induced on the secondary coil L2 is limited. Because the change in current is limited, corruption of communication from areceiver 202 to atransmitter 128 in awireless transmission system 200 is reduced. - The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiments were chosen and described in order to best explain the applicable principles and their practical application to thereby enable others skilled in the art to best utilize various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments except insofar as limited by the prior art.
Claims (20)
1. A circuit comprising:
a rectifier circuit coupled to a first current path;
a communication switch coupled to the first current path; and
a charge control circuit including:
a charge control input coupled to the first current path;
a charge control output;
a transistor including a first terminal coupled to the charge control input, a second terminal coupled to the charge control output, and a control terminal; and
a first operational amplifier including a first input coupled to a second current path, a second input coupled to a voltage reference, and an output coupled to the control terminal of the transistor.
2. The circuit of claim 1 , wherein:
the charge control circuit includes a current sensor; and
the first current path and the second current path are coupled to the current sensor.
3. The circuit of claim 1 , wherein:
a load is coupled to the charge control output.
4. The circuit of claim 1 , wherein:
the charge control circuit includes a second operation amplifier and a first resistor; and
the second operational amplifier includes a first input coupled to the second current path, a second input, and an output coupled to a first terminal of the first resistor.
5. The circuit of claim 4 , further including:
a capacitor including a first terminal coupled to a second terminal of the first resistor, and a second terminal of the capacitor coupled to a ground terminal.
6. The circuit of claim 5 , wherein:
the first resistor and the capacitor are configured as a low-pass filter.
7. The circuit of claim 5 , wherein:
the second terminal of the first resistor and the first terminal of the capacitor are coupled to the second input of the first operational amplifier.
8. The circuit of claim 5 , wherein:
the output of the second operational amplifier is coupled to a first terminal of a second resistor;
the second input of the second operational amplifier is coupled to a second terminal of the second resistor;
the second input of the second operational amplifier and the second terminal of the second resistor is coupled to a first terminal of a third resistor; and
a second terminal of the third resistor is coupled to the ground terminal.
9. The circuit of claim 8 , wherein:
the charge control circuit includes a fourth resistor; and
a first terminal of the fourth resistor is coupled to the second current path and a first input of the second operational amplifier.
10. The circuit of claim 1 , wherein:
the charge control circuit includes a current source coupled to the first terminal of the transistor and the control terminal of the transistor.
11. A receiver comprising:
a rectifier circuit coupled to a first current path;
a communication switch coupled to the first current path; and
a charge control circuit including:
a charge control input coupled to the first current path;
a charge control output;
a transistor including a first terminal coupled to the charge control input, a second terminal coupled to the charge control output, and a control terminal; and
an operational amplifier including a first input coupled to a second current path, a second input coupled to a voltage reference, and an output coupled to the control terminal of the transistor.
12. The receiver of claim 11 , wherein:
a load is coupled to the charge control output.
13. The receiver of claim 11 , wherein:
the charge control circuit includes a current sensor; and
the first current path and the second current path are coupled to the current sensor.
14. The receiver of claim 13 , wherein:
the charge control circuit includes a first resistor and a second resistor;
a first terminal of the first resistor is coupled to the current sensor;
a second terminal of the first resistor is coupled to a first terminal of the second resistor; and
a second terminal of the second resistor is coupled to a ground terminal.
15. The receiver of claim 14 , wherein:
the charge control circuit includes an analog-to-digital converter (ADC); and
an input of the ADC is coupled to the current sensor and the first terminal of the first resistor.
16. The receiver of claim 15 , wherein:
the charge control circuit includes a digital-to-analog converter (DAC);
an output of the ADC is coupled to an input of the DAC;
an output of the DAC is coupled to the first input of the operational amplifier; and
the second input of the operational amplifier is coupled to the second terminal of the first resistor and the first terminal of the second resistor.
17. A system comprising:
a transmitter; and
a receiver including:
a rectifier circuit coupled to a first current path;
a communication switch coupled to the first current path; and
a charge control circuit including:
a charge control input coupled to the first current path;
a charge control output;
a transistor including a first terminal coupled to the charge control input, a second terminal coupled to the charge control output, and a control terminal; and
a first operational amplifier including a first input coupled to a second current path, a second input coupled to a voltage reference, and an output coupled to the control terminal of the transistor.
18. The system of claim 17 , wherein:
the charge control circuit includes a second operation amplifier and a first resistor; and
the second operational amplifier includes a first input coupled to the second current path, a second input, and an output coupled to a first terminal of the first resistor.
19. The system of claim 17 , wherein:
the charge control circuit includes an analog-to-digital converter (ADC) and a current sensor;
the current sensor is coupled to the first current path and the second current path; and
an input of the ADC is coupled to the current sensor.
20. The system of claim 19 , further including:
the charge control circuit includes a digital-to-analog converter (DAC); and
an output of the ADC is coupled to an input of the DAC; an output of the DAC is coupled to the first input of the first operational amplifier.
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US16/540,964 US11569673B2 (en) | 2009-07-21 | 2019-08-14 | Charge control circuitry in a wireless power receiver |
US18/095,956 US20230163617A1 (en) | 2009-07-21 | 2023-01-11 | Reducing corruption of communication in a wireless power transmission system |
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2010
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2018
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US20180301942A1 (en) | 2018-10-18 |
US11569673B2 (en) | 2023-01-31 |
US9318897B2 (en) | 2016-04-19 |
US20190372397A1 (en) | 2019-12-05 |
US20110163608A1 (en) | 2011-07-07 |
US9954402B2 (en) | 2018-04-24 |
US20160308400A1 (en) | 2016-10-20 |
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