MXPA99004388A - Supply of reserve energy for dedespliegue de vi department - Google Patents

Abstract

A switched-mode power supply circuit for a video display apparatus having operating modes of operation and reserve. An operation mode power supply (T1, Q1) provides an output voltage (Vn3, Vn4) for the video display apparatus during the operation mode of operation. A reserve mode power supply (T2, Q51) provides an output voltage for the video display apparatus during the standby mode of operation. A switch mode power supply controller circuit (20) provides excitation pulses (30) to the operation mode power supply (T1, Q1) during the operation mode and to the reserve mode power supply (T2, Q51) during reservation mode. A protection circuit (60) of the standby power supply is used to turn off a start transistor during the standby operation mode to avoid energy dissipation in a start resistor.

Description

SUPPLY OF RESERVE ENERGY FOR VIDEO DEPLOYMENT DEVICE BACKGROUND Field of the Invention This invention relates generally to the field of energy supplies, and in particular, to standby power supplies for video display apparatus such as, for example, television receivers. BACKGROUND OF THE INVENTION The power consumption of a video display apparatus can approach, or even exceed, approximately ten watts during the standby operation mode. In an era of increased government interest in energy efficiency standards for electronic equipment, such a level of standby power consumption represents a concern. For example, a September 19, 1997 article in the Europe Energy publication reports that the European Commission considers reducing the energy consumed by electronic equipment in the reserve operation mode a priority. In addition, the article states that the Commission has concentrated its initial efforts on reducing the reserve energy consumption of television sets and video recorders, and has established voluntary committees of manufacturers of these products to progressively reduce the reserve energy consumption. average to less than three watts. A conventional power supply configuration for a video display apparatus is disclosed in Japanese Patent Laid-Open No. JP 6-225529. An output stage of operation mode 2 is coupled to a converter 1 via a switch SW, and a reserve mode output stage 3 is inseparably connected to the converter 1. The configuration disclosed in J P 6-225529 is undesirably inefficient because the reserve mode output stage 3 dissipates energy during the operation mode of operation. In another conventional power supply configuration for a video display apparatus, a single power supply circuit is used to implement the operation and reserve operation modes. When the power supply control circuit detects that the secondary side of the power supply is discharged, the power supply is placed in a "surge" mode of standby operation, where the power supply continues to generate voltages of reservation for the remote control receiver and the microcontroller. A disadvantage of this conventional implementation of power supply is that the primary inductance of the switched-mode power supply transformer is too low for adequate reserve operation. This low primary inductance produces an increase in power consumption in the video display apparatus in standby mode. The reduction in energy consumed by the video display apparatus during the standby operation mode dictates that the pulse width of the drive pulses of the power supply control circuit be reduced; or else, that the inductance seen by the excitation pulses during the reserve mode is increased in relation to the inductance of the primary winding of the switched-mode power supply transformer. Due to the limitations imposed on the pulse width by the control circuit of the power supply, it is desirable to increase the inductance seen by the excitation pulses during the reserve mode, in order to reduce the power consumption of the display device. video during the reserve operation mode, preferably at a level equal to or less than one watt. Brief Description of the Invention The present invention is directed to increasing the inductance seen by the driving pulses of a power supply control circuit during the standby operation mode. A switched-mode power supply circuit in accordance with the present invention comprises: a power supply mode of operation for providing an output voltage for the video display apparatus during the operating mode of operation; a reserve mode power supply for providing an output voltage for the video display apparatus during the standby mode of operation; and a switched-mode power supply driver circuit for providing drive pulses to the mode power supply during operation mode and reserve mode power supply during the standby mode. The foregoing and other aspects, functions and advantages of the present invention will be apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a diagram in block form and schematic form of a reserve mode power supply including the present invention; and Figures 2 and 3 are schematic diagrams of particular implementations of the reserve mode power supply of Figure 1. Description of Preferred Modes A dual switched mode power supply circuit 100 shown in Figure 1 includes a configuration of the invention for a reserve mode power supply for a television receiver. The power supply circuit 100 utilizes two switched-mode power supplies: an operation mode power supply using a return transformer T1 and a reserve mode power supply using a return transformer T2. The operation transformer T1 is used during the operation mode of operation of the television receiver. The operating transformer T1 has a primary winding n 1 having a first terminal 1 1 coupled to the rectified main voltage 10 and a second terminal 12 coupled to an operating power switch Q 1. The secondary winding n2 is coupled to the control circuit of the switched mode power supply 20, and secondary windings n3 and n4 provide voltages which, after being rectified by diodes D5 and D4, respectively, are used to energize other circuits in the television receiver. For example, the secondary winding n3 is used to energize the microcontroller (not shown) and the remote control receiver when the television receiver operates in a standby mode. The operating power switch Q 1 and the backup power switch Q51 are controlled by the switched mode power supply controller circuit 20. In the standby operation mode, the first switch S1 is open and the second switch S2 It is closed, as shown in Figure 1. The control electrode 13 of the energy switch Q1 is coupled to the ground or reference potential, and then the power switch Q 1 is turned off. The drive pulses 30 at the output of the switch mode power supply controller circuit 20 are coupled to the control electrode 16 of the backup power switch Q51 via the resistor R55. As the reserve power switch Q51 switches in response to the excitation pulses 30, energy is transferred from the primary winding n51 of the backup transformer T2 to the secondary winding n53. The voltage across the secondary winding n53 is rectified by the diode D57 to provide the voltage Vn3 to the microcontroller and the remote control receiver. During the operating operation mode of the television receiver, the first switch S 1 is closed and the second switch S 2 is open. Now, the control electrode 16 of the reserve power switch Q51 is coupled to the ground or reference potential and the reserve power switch Q51 is off. The excitation pulses 30 at the output of the switching mode power supply controller circuit 20 are coupled to the control electrode 13 of the operating power switch Q1 through the resistor R10. When the operating power switch Q1 switches in response to the excitation pulses 30, the energy is transferred from the primary winding n 1 of the operating transformer T1 to the secondary windings n3 and n4. The voltages through the secondary windings n3 and n4 are rectified by diodes D5 and D4, respectively, to energize other circuits in the television receiver. Figure 2 illustrates a currently preferred mode of the dual switched mode power supply circuit 100, which uses field effect transistors for the operating energy switch Q1 and the backup power switch Q51. The operating transformer T1 may comprise a conventional design for switched mode power supply applications, and will not be further described herein. The backup transformer T2 used in the preferred embodiment of Figure 2 was constructed using an E16 type core with a total air space of 0.1 mm. Primary winding n51 has approximately 500 turns of 0.1 mm CuN wire (copper wire with nylon insulation). The secondary winding n52 has approximately 60 turns and the secondary winding n53 has approximately 24 turns.

Approximately 5 layers of MYLAR® polymer film with a thickness of 0.1 mm provide electrical insulation between the primary winding n51 and the secondary windings n52 and n53. The inductance of the primary winding n51 is equal to about 70 mH, which is relatively large compared to the inductance of the primary winding n 1 of the operating transformer T1. This relatively high inductance is necessary to accommodate the use of the switched mode power supply circuit 20 with the backup transformer T2. The reduction in energy consumed by the video display apparatus during the standby operation mode dictates either that the pulse width of the drive pulses 30 of the switched mode power supply controller circuit 20 are reduced; or, that the inductance seen by the excitation pulses 30 during the reserve mode is increased in relation to the inductance of the primary winding n 1 of the operating transformer T1. The relatively high inductance of the primary winding n51 of the backup transformer T2 is used because the excitation pulses 30 of the switch mode power supply controller 20 can not have a pulse width that is less than a minimum pulse width. A common minimum pulse width may be equal, for example, to approximately one microsecond. Due to the relatively high inductance of the primary winding n51 of the backup transformer T2, the excitation pulses 30 have a substantially similar frequency and duty cycle regardless of whether they are applied to the operating power switch Q1 in the operating mode or to the switch of reserve power Q51 in reservation mode. The power supply circuit 100 has a separate feedback path for the operating and reserve operation modes of the television receiver. In the operation mode of operation, a voltage is fed back into the terminal 17 of the operation transformer T1 to the switching mode power supply controller circuit 20. In the currently preferred mode of Figure 2, the power supply controller circuit The switched mode 20 may comprise, for example, an integrated circuit of the power supply controller TDA4605 manufactured by Siemens Aktiengesellschaft. The following voltages are fed back from terminal 17 of secondary winding n2 to controller circuit 20: a supply voltage to pin 6 of controller circuit 20 through diode P 1; a zero detector voltage to pin 8 of the controller circuit 20 through the resistors R8 and R9 and the capacitor C6; and a regulator voltage to pin 1 of the controller circuit 20 through the resistor R9, the capacitor C6, and the diode D2. In the reserve operation mode, a voltage at the terminal 18 of the backup transformer T2 is fed back to the switching mode power supply controller circuit 20. The following voltages are fed back from the terminal 18 of the secondary winding n52 to the controller circuit 20 : a supply voltage to pin 6 of the controller circuit 20 through the diode D51; a zero detector voltage to pin 8 of the controller circuit 20 through the resistors R52 and R53 and the capacitor C51; and a regulator voltage to pin 1 of the controller circuit 20 through the resistor R53, the capacitor C51, and the diode D52. When the television receiver is in a standby mode of operation, the current that flows through the light emitting diode of the optocoupler 40 is equal to about zero. Thus, transistor Q53 is turned off and excitation pulses 30 of leg 5 of controller circuit 20 are applied to control electrode 16, or gate electrode, of reserve power switch Q51. When the excitation pulses 30 turn on the reserve power switch Q51, the base electrode of the excitation transistor Q52 is coupled to ground or reference potential, through the diode D55 and the reserve power switch Q51; the excitation transistor Q52 and the operating energy switch Q 1 are turned off in this manner. The voltage at the leakage electrode of the backup power switch Q51 can be used in this way to control the excitation transistor Q52, and hence the operating power switch Q1, because the reserve power switch Q51 can switch over Quickly than the operating power switch Q1. As the reserve power switch Q51 switches in response to the excitation pulses 30, energy is transferred from the primary winding n51 of the backup transformer T2 to the secondary winding n53. The voltage across the secondary winding n53 is rectified by the diode D57 to provide the voltage Vn3 to the microcontroller and the remote control receiver. When the television receiver is in the operating mode or "TV on", the current Idiode flowing through the light emitting diode of the optocoupler 40 is equal to about two milliamps. This turns on the opto-coupler transistor 40, thereby coupling a supply voltage, equal to about + 12 V in the preferred embodiment shown in Figure 2, to the base electrode of transistor Q53 through the voltage divider formed by resistors R57. and R58. The transistor Q53 is turned on, bringing the control electrode 16, or gate electrode, from the reserve power switch Q51 to the ground or reference potential. Then, the backup power switch Q51 is turned off and the voltage at the leakage electrode of the backup power switch 51 is raised to a high level. As a consequence, the diode D55 is reverse biased and the excitation pulses 30 are applied through the resistor R54 to the base electrode of the excitation transistor Q52 and through the resistor R 10 to the collector electrode of the exciting transistor Q52. Then, the excitation transistor Q52 activates the operating power switch Q1 which responds to the drive pulses 30. When the operating power switch Q1 switches in response to the excitation pulses 30 and the excitation transistor Q52, the power it is transferred from the primary winding n 1 of the operating transformer T1 to the secondary windings n3 and n4. The voltages through the secondary windings n3 and n4 are rectified by diodes D5 and D4, respectively, to energize other circuits in the television receiver. The anode of the diode D56 is coupled to the emitting electrode of the exciting transistor Q52 and the cathode of the diode D56 is coupled to a terminal of the resistor R56. The other terminal of resistor R56 is coupled to the base electrode of transistor Q53. This series connection of the diode D56 and the resistor R56 keeps the transistor Q53 turned on when the operating power switch Q1 is turned on, thus ensuring that the reserve power switch Q51 does not turn on when the operating power switch Q1 is turned on . The diode D54 is coupled in parallel with, and with opposite pole to the excitation transistor Q52. The diode D54 and the resistor R10, which couples the output leg 5 of the controller circuit 20 to the collector electrode of the excitation transistor 52, couple a path to discharge the gate capacitance of the operating energy switch Q 1, thus enabling the operating power switch goes off. When the television receiver is switched from the standby mode to the operating mode, the output capacitors are discharged, for example the capacitor C8 in FIG. 2. Then, when the operating power switch Q 1 is turned on for the first time in In the operating mode after the standby mode switch, an excessively high peak current can flow through the operating power switch Q1, possibly destroying it. Excessively high current is a consequence of the function of a return system that requires a relatively long time to transfer energy from a primary winding of a return transformer, for example the primary winding n 1 of the operating transformer T1, to a secondary side of the return transformer, for example, the secondary winding n4 of the operating transformer T1, if the voltage on the secondary side of the return transformer is relatively low . To protect the operating energy switch Q1 from destruction due to an excessively high peak current flowing therethrough, a small current is fed to the leg 1 of the controller circuit 20 through the resistor R51. The magnitude of the current is ata (+02 V / R51) which for the mode shown in Figure 2 is equal to approximately 26 micro-amperes. This current simulates a high feedback voltage on pin 1 of the controller circuit 20, which causes the controller circuit 20 to go into a "no-load" mode or a "sudden rise" mode, wherein the pulse widths of the excitation pulses 30 are reduced to their minimum width. The width of the excitation pulses 30 increases and eventually returns to a nominal width when the output capacitors are charged. A protection circuit 60 formed by the series combination of the capacitor C52 and the diode D53 is coupled in parallel with the primary winding n51 of the backup transformer T2. In one aspect of the present invention, the protection circuit 60 is used to control the current in the starting resistor R 1. During the reserve operation mode of the television receiver, when the driving circuit 20 applies the excitation pulses 30 to the control electrode 16, or gate electrode, of the reserve power switch Q51, a voltage Vs at the junction of the capacitor C52 and the diode D53 that greater than the rectified main line voltage at the emitting electrode of the starting transistor Q54 . The start transistor Q54 is turned off, no current flows through the start resistor R1 during the standby mode and, as a consequence, the power consumption is reduced during standby mode. Although not shown in Figure 2, the protection network 61 of the primary winding n 1 of the operation transformer T1 could also be used to turn off the start transistor Q54, by coupling a junction of the capacitor C7 and the diode D3 to the start transistor through a resistance of appropriate value. Figure 3 shows a dual switched mode power supply circuit 100 ', which uses a bipolar junction transistor for the backup power switch Q51'. Although shown in Figure 1 using a field effect transistor, the reserve power switch Q51 can be implemented using either a field effect transistor or a bipolar junction transistor, as will be seen in Figures 2 and 3 Although not shown in Figures 1-3, the operating energy switch Q1 can also be implemented using a bipolar junction transistor. The use of a bipolar junction transistor for the operating power switch Q1 would require a different controller circuit 20, for example an integrated power supply controller circuit TDA4601 manufactured by Siemens Aktiengesellschaft; a specific excitation circuit for the bipolar junction transistors will also be required. Such modifications are obvious to those skilled in the art. The embodiment shown in Figure 3 operates substantially in the same manner as the modality shown in Figure 2. A difference between the field effect transistor and the bipolar junction transistor is that the ignition time of a bipolar transistor is longer than that of a field effect transistor. Therefore, unlike the embodiment shown in Figure 2, wherein the voltage at the electrode of the backup power switch Q51 was used to control the excitation transistor Q52 and hence the operating energy switch Q 1, the voltage at the collector electrode of the reserve power switch Q51 'can not be used to control the excitation transistor Q52. In the mode shown in Figure 3, the excitation transistor Q52 is controlled by the optocoupler 40 through the transistor Q55. The excitation circuit for the backup power switch Q51 comprises the resistors R55 and R61, the capacitor C53, and the diodes D59 and D60; The operation of this excitation circuit is well known to those skilled in the art and will not be further described herein. In standby mode, the opto-coupler transistor 40 does not conduct, so that transistor Q53 is off and standby power switch Q51 is consequently switching in response to the drive pulses 30 of controller circuit 20. Concurrently, the transistor Q55 is turned on so that the excitation transistor Q52 and the operating power switch Q1 are turned off. On the contrary, in the operating mode, the transistor of the optocoupler 40 drives; the transistor Q53 is turned on and the reserve power switch Q51 is consequently turned off; transistor Q55 is off; and the excitation transistor Q52 energizes the operating power switch Q1 in response to the drive pulses 30 of the controller circuit 20. The present invention in the mode of the dual switched mode power supply circuits 100 and 100 'of the Figures 2 and 3, advantageously reduces the energy consumed by a television receiver operating in standby mode. For example, assuming a load equal to approximately 200 mW, which approximates a standard microcontroller operating in the operating mode, the energy consumed by the television receiver can be reduced from approximately six watts to approximately one watt using the configurations of the invention described herein. It will be apparent to those skilled in the art that, although the invention has been described in terms of specific examples, modifications and changes can be made without departing from the spirit of the invention. Accordingly, reference should be made to the appended claims rather than to the above specification, as indicated by the true scope of the invention.

Claims (29)

1. CLAIMS 1. A power supply circuit for an apparatus having operation and reserve modes of operation comprising: a. output stage of operating mode (T1, Q1) to provide an operating mode output voltage (Nv3, Vn4) during such operation mode of operation; a reserve mode output stage (T2, Q51) for providing a reserve mode output voltage (Vn3) during said reserve operation mode; and a control circuit (20, S1, S2) coupled to such operating and reserve mode output stages to provide excitation pulses (30) to only one of said output stages (T1, Q1; T2, Q51) ) during each of the mentioned modes of operation. The power supply circuit of claim 1, wherein said operating mode output stage comprises: an operating transformer (T1) having a primary winding (n 1) and providing such an output voltage so as to operation (Vn3, Vn4); and an operating power switch (Q1) coupled uninterrupted to said primary winding (n 1) of said operating transformer (T1) to control the current flow in said primary winding (n 1) which responds to those mentioned Excitation pulses (30). 3. The power supply circuit of claim 2, wherein said operating energy switch comprises a transistor. The power supply circuit of claim 2, wherein said reserve mode output stage comprises a backup transformer (T2) having a primary winding (n51) which has sufficient inductance to cause such pulses of excitation (30) have a duty cycle in said reserve operation mode that is not less than a minimum duty cycle that such a control circuit is capable of providing. The power supply circuit of claim 4, wherein said primary winding (n51) has sufficient inductance to cause such excitation pulses (30) to have a frequency in said reserve operation mode that is not less than that a minimum frequency that such a control circuit is capable of providing. The power supply circuit of claim 1, wherein said control circuit comprises switching means (40, R10, R54, $ 57, R55, R58, Q52, Q53, D55) for coupling such excitation pulses (30). ) only to said operating power switch (Q1) during such operation mode of operation and only to said backup power switch (Q51) during said reserve operation mode. The power supply circuit of claim 6, wherein said switching means comprises a first switch (Q53) for controlling said backup power switch (Q51) that responds to the mode of operation of such an apparatus. The power supply circuit of claim 6, wherein said first switch (Q53) turns off said backup power switch (Q51) during said operating mode of operation. The power supply circuit of claim 6, wherein said switching means further comprises: a transistor (Q52) for providing said excitation pulses (30) to said operating power switch (Q1) during said mode operating operation; and a diode (D55) having an anode coupled to a control electrode of such a transistor (Q52) and a cathode coupled to said backup power switch (Q51), said diode conducts and prevents such a transistor (Q52) from being turn on when the aforementioned backup power switch (Q51) is on. 10. The power supply circuit of claim 9, further comprising a diode (D56) having an anode coupled to an output electrode of said transistor (Q52) and a cathode coupled to a control electrode of said first switch (Q53) , such diode (D56) conducts and prevents such reserve power switch (Q51) from switching during such operation mode of operation. 11. A power supply circuit for an apparatus having operating and reserve operating modes, comprising: a source of voltage potential (RECTIFYED PRENTIAL PRIOR LINE); a control circuit (20) for providing excitation pulses (30) at an output; a start circuit (Q54, Rl) that couples the source (RECTIFYED PRI NICLE MAIN LINE) to a control input of such control circuit to activate the operation of such control circuit (20); a backup transformer (T2) having a primary winding (n51) and a secondary winding (n53) to provide an output voltage (Vn3) during such reserve operation mode; and a protection circuit (60) coupled to said primary winding (n51) of said backup transformer (T2) and further coupled to said starter circuit (Q54, R1). 12. The power supply circuit of the claim 11, wherein said protection circuit (60) comprises a series combination of a capacitor (C52) and a diode (D53). 13. The power supply circuit of the claim 12, wherein said junction of said capacitor (C52) and said diode (D53) is coupled to said starting circuit (Q54, R51). 14. The power supply circuit of the claim 13, wherein a cathode of said diode (D53) is coupled to the starting circuit (Q54, R51). The power supply circuit of claim 14, wherein said starting circuit comprises: a starting resistor (R1) having a first terminal coupled to said control input of the control circuit (20); and a start transistor (Q54) having a control electrode, a first electrode coupled to such a voltage potential source (RECTIFYED MAIN MAIN LINE) and a second electrode coupled to a second terminal of such a starting resistor (R1) . 16. The power supply circuit of claim 15, wherein a junction of said capacitor (C52) and said diode (D53) is coupled to said control electrode of said start transistor (Q54). 17. A power supply circuit for an apparatus having operational and reserve operating modes comprising: u? control circuit (20) for providing excitation pulses (30) at an output; an operating transformer (T1) having a primary winding (n51) and a secondary winding (n3, n4) to provide an output voltage (Vn3, Vn4) for said apparatus during said operating mode of operation; an operating power switch (Q 1) coupled to said primary winding (n 1) of said operating transformer (T1) for controlling the current flow in said primary winding that responds to said driving pulses (30); a backup transformer (T2) having a primary winding (n51) and a secondary winding (n53) to provide an output voltage (Vn3) for such an apparatus during said reserve operation mode; a reserve power switch (Q51) coupled to said primary winding (n51) of said backup transformer (T2) to control the flow of current in said primary winding that responds to said excitation pulses (30); and a switching configuration (40, R10, R54, R57, R55, R58, Q52, Q53, D55) to couple such excitation pulses (30) exclusively to either said operating energy switch (Q1) or to said backup power switch (Q51) during a particular mode of operation of such an apparatus. 18. The power supply circuit of the claim 17, wherein said switching configuration comprises a first switch (Q53) for controlling said backup power switch (Q51) that responds to the operation mode of said apparatus. 19. The power supply circuit of the claim 18, wherein said first switch (Q53) turns off such reserve power switch (Q51) during the reserve operation mode. 20. The power supply circuit of the claim 19, further comprising: a transistor (Q52) for providing said excitation pulses (30) to said operating energy switch (Q1) during said operating mode of operation; and a diode (D55) having an anode coupled to a control electrode of such a transistor (Q52) and a cathode coupled to said backup power switch (Q51), such a diode (D55) conducts and prevents said transistor (Q52) ) lights when the aforementioned reserve power switch (Q51) is turned on. 21. The power supply circuit of the claim 20, further comprising a diode (D56) having an anode coupled to an output electrode of said first switch (Q53), such diode (D56) conducts and prevents said reserve power switch (Q51) from switching during said mode operating operation. 22. A power supply circuit for an apparatus having operation and reserve modes of operation comprising: a source of excitation pulses (30), said source providing such excitation pulses (30) at an output; an operating transformer (T1) to provide an output voltage (Vn3, Vn4) for said apparatus during said operating operation mode, such an operating transformer (t1) has a primary operating winding (n1) having a primary inductance of operation; an operating power switch (Q1) coupled to said output and coupled to said primary winding (n1) of such an operating transformer (T1); a backup transformer (T2) for providing an output voltage (Vn3) for said apparatus during said reserve operation mode, such a backup transformer (T2) having a primary backup winding (n51) having a primary inductance of reserve that is greater than such primary inductance of operation; and a backup power switch (Q51) coupled to said output and coupled to said primary winding (n51) of said backup transformer (T2). 23. The power supply circuit of claim 22, wherein said prime reserve inductance is sufficient to cause such excitation pulses (30) to have a duty cycle in said reserve mode of operation which is not less than that a minimum work cycle can be provided by such a control circuit. The power supply circuit of claim 23, wherein said primary winding (n51) has sufficient inductance to cause such excitation pulses (30) to have a frequency in said standby operation mode which is not less than a minimum frequency capable of being provided by such a control circuit. 25. A power supply circuit for an apparatus having operating modes and reserve, comprising: a source (+ 12 V) of voltage potential; a control circuit (20) for providing excitation pulses (30) at an output; an operating mode output stage (T1, Q1) having an operating power switch (Q1) coupled to such output to provide an operating mode output voltage (Vn3, Vn4) during such operation mode of operation; a reserve mode output stage (T2, Q51) having a reserve power switch (Q51) coupled to such an output to provide a reserve mode output voltage (Vn3) during said reserve operation mode; and means (40) for controlling such power mode and standby mode switches (Q1, Q51) that respond to a change in the mode of operation of said apparatus. 26. The power supply circuit of the claim 25, wherein said control means comprises a first switch (Q53) for controlling said backup power switch (Q51) that responds to such a source (+ 12 V) of potential voltage. 27. The power supply circuit of the claim 26, wherein said first switch (Q53) turns off such backup power switch (Q51) during said operating mode of operation. 28. The power supply pircuite of the claim 26, wherein said control means further comprises: a transistor (Q52) for providing such driving pulses (30) to said operating power switch (Q1) during such operation mode of operation; and a diode (D55) having an anode coupled to a control electrode of said transistor (Q52) and a cathode coupled to said backup power switch (Q51), said diode conducts and prevents such a transistor (Q52) from being turned on when the aforementioned reserve power switch (Q51) is turned on. 29. The power supply circuit of the claim 28, further comprising a diode (D56) having an anode coupled to an output electrode of said transistor (Q52) and a cathode coupled to a control electrode of said first switch (Q53), said diode (D56) conducts and avoids that such backup power switch (Q51) switches during such operation mode of operation.