JP2008136323A - Power supply circuit and plasma display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an overvoltage state of a start-signal emitting part and a secondary-side circuit and to protect overvoltage of IC in one input terminal, in a power supply circuit that uses ICs having overvoltage protection function that receives a signal for starting oscillation from the input terminal, detecting the overvoltage state of the inputted signal and stopping the oscillation. <P>SOLUTION: The drive power supply circuit that generates and controls an AC power supply, in a resonance circuit 11, based on power inputted from a main power supply circuit is provided with an overvoltage signal supply part 11c that receives the overvoltage state from a secondary side in a resonance drive part 11b of the resonance circuit 11 via a feedback transformer 14 and generating the overvoltage signal, based on the received signal. As a result of this, the overvoltage signal is inputted to the terminal protecting overvoltage of IC11a, and overvoltage protection of IC11a is carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a power supply circuit having an IC having an overvoltage detection function at a start terminal, and a plasma display device using the power supply circuit.

  FIG. 6 is a diagram illustrating the internal logic of an IC having an overvoltage detection function at a start terminal that receives a signal for oscillation. From the figure, the IC 1 includes a start terminal 2 that receives a start signal for oscillation, a feedback terminal 3 that receives a predetermined voltage and controls oscillation of the IC 1, a source terminal 4, a drain terminal 5, and a ground terminal 6. It has a terminal. Further, IC1 has internal logic as a start block 7a for starting oscillation, an overvoltage detection block 7b for detecting an overvoltage state of an input signal, an oscillation control block 7c for controlling oscillation in IC1, and a transmission And a base frequency generation circuit (OSC circuit) 7d. As for the relationship between each terminal and block described above, the start terminal 2 is connected to the start block 7a and the overvoltage detection block 7b in parallel inside the IC, and monitors the overvoltage state of the start signal input from the start terminal 2. Yes.

  When the overvoltage detection block 7b detects the overvoltage state of the start signal, the IC 1 shifts to the latch mode. In the latch mode described above, the IC 1 stops oscillating until the input of the start signal is temporarily stopped regardless of the voltage state of the start signal. The feedback terminal 3 is connected to the oscillation control block 7c inside the IC, and performs oscillation control of the frequency generation circuit 7d based on the input feedback signal.

  As a method of using the IC 1 having the above-described configuration, a power circuit using a resonance circuit for converting a DC power source into an AC power source can be mentioned. In such a power supply circuit, a control unit such as a microcomputer is connected to the start terminal, and a secondary circuit connected through a transformer is connected to the feedback terminal 3 for use. Therefore, the IC 1 starts oscillation of the IC 1 by a start signal output from the microcomputer and controls the oscillation of the IC 1 by a feedback signal output from the secondary side circuit. In such a method of using the IC1, when the microcomputer operates abnormally, the IC1 stops oscillation by detecting the overvoltage state of the start signal by the overvoltage detection block 7b, and when the secondary side circuit operates abnormally, the feedback signal Is controlled by the oscillation control block 7c.

  As described above, the overvoltage state due to the abnormal operation of the secondary side circuit is controlled by the oscillation control block 7c according to the value of the feedback signal input via the feedback terminal 3 to protect the IC1. However, the oscillation control of IC1 by the oscillation control block 7c takes a predetermined time. Therefore, in the case of the overvoltage state of the secondary side circuit, more preferably, the oscillation of IC1 is instantaneously stopped and the IC1 is switched to the latch mode. It is more desirable to protect. The following invention is disclosed as a method of stopping the oscillation of the IC 1 by detecting the overvoltage state of the secondary side circuit using the overvoltage protection function in the IC. That is, when the secondary side circuit and the start terminal of the IC are connected by a Zener diode, and the secondary side circuit is in an overvoltage state, the Zener diode breakdown current is mainly used. As a result, a signal based on the breakdown current is mainly applied to the start terminal of the IC, and the overvoltage protection function is differentiated (see, for example, Patent Document 1).

  Further, in a power supply circuit that is driven by combining two switching means in parallel, the following method is disclosed in order to prevent the circuit from being damaged due to an increase in load on one side when one side is open. . That is, the current detection means for individually detecting the current flowing through the two switching means, the comparison means for individually comparing the outputs of the respective current detection means, and the flow to any one of the switching means based on the comparison result of the comparison means And a control means for controlling the load (see, for example, Patent Document 2).

Further, a method is disclosed in which a latch-off circuit is externally attached to an IC that does not have a stop function by latching to economically protect the IC from overcurrent and overvoltage (see, for example, Patent Document 3).
JP 2005-124246 A JP 2000-323975 JP-A-6-153382

  The invention of Patent Document 1 described above has the following problems. That is, the invention of Patent Document 1 is to reduce the number of parts by replacing a connecting part such as a photocoupler that connects a secondary circuit and an IC with a Zener diode. Therefore, the oscillation control of the IC is performed by the feedback terminal at the normal startup as in the present case, and the overvoltage protection function in the IC is not realized only when the overvoltage state of the secondary side circuit is detected.

  Further, the invention of Patent Document 2 has the following problems. The present invention is limited to a power supply circuit using two switching means (IC in the present invention), and cannot be applied to a circuit for detecting an overvoltage by one IC as in the present invention.

  Further, the invention of Patent Document 3 has the following problems. That is, the present invention is limited to an IC that does not have a latch-off circuit therein, and does not disclose a method for detecting an overvoltage state of a secondary circuit as in the present invention by an overvoltage protection circuit in the IC.

  The present invention has been made in view of the above problems, and an IC having an overvoltage protection function that receives a signal for starting oscillation from an input terminal, detects an overvoltage state of the input signal, and stops oscillation. Provided are a power supply circuit that uses a single input terminal to detect an overvoltage state of a start signal transmission unit and a secondary circuit, and protects an IC from overvoltage, and a plasma display device using the power supply circuit. With the goal.

  In order to solve the above-mentioned problem, in the power supply circuit according to claim 2, an IC having an overvoltage protection function for receiving an oscillation start signal and detecting an overvoltage state of the input signal to stop oscillation, In the power supply circuit having a start signal transmission unit that supplies a start signal for oscillating the IC to the input terminal, and a secondary circuit that generates a predetermined voltage based on the oscillation of the IC, the secondary circuit When the side circuit is in an overvoltage state, an overvoltage signal supply unit is provided that outputs an overvoltage signal to the input terminal of the IC by feedback to differentiate the overvoltage protection function of the IC.

  In the invention configured as described above, the input terminal of the IC is connected in parallel to the start signal transmission unit and the secondary circuit, and the feedback terminal of the IC is connected to the secondary circuit. The input terminal and the secondary side circuit are connected via an overvoltage signal supply unit. Therefore, in normal times, the start signal from the start signal transmission unit is received and oscillation is started, and the abnormal operation of the overvoltage signal supply unit is monitored by the overvoltage protection function to protect the IC overvoltage. Furthermore, the feedback signal from the secondary side circuit is received and oscillation control in the IC is performed. At this time, if the secondary circuit falls into an overvoltage state due to an abnormal operation or the like, the overvoltage signal supply unit detects the abnormality and outputs an overvoltage signal to the input terminal of the IC, so that the oscillation of the IC is promptly performed. Stop.

  Therefore, in an IC having an overvoltage protection function that accepts a signal for starting oscillation from the above-described input terminal and detects an overvoltage state of the input signal and stops oscillation, an abnormality of the start signal is detected at one terminal. The overvoltage protection of the IC can be performed by detecting the overvoltage state of the secondary side circuit.

  Further, as an example of a specific configuration of the power supply circuit according to the present invention, in the invention according to claim 3, the IC is incorporated in a resonance circuit that converts a DC power supply on the primary side into AC by resonance. The AC power converted by the resonance circuit is supplied to the secondary circuit via a transformer, and the overvoltage signal supply unit is incorporated in the resonance circuit and is output from the secondary circuit via a feedback transformer. The overvoltage signal is generated based on the voltage value of the feedback signal.

  In the invention configured as described above, an IC that oscillates is often used mainly in a resonance circuit. In this case, the resonance circuit converts a DC power source from the primary side to AC and outputs it to the secondary side. Used for. At this time, the overvoltage signal supply unit outputs an overvoltage signal based on the feedback signal output from the secondary circuit via the feedback transformer. Therefore, since an overvoltage signal is generated using a feedback signal, a signal generation source is not required and the circuit configuration can be simplified.

  As an example of a specific configuration constituting the overvoltage protection function in the IC, in the invention according to claim 4, when the overvoltage signal having a predetermined voltage is output, the IC shifts to the latch mode. It has a configuration having an overvoltage protection function for stopping oscillation.

  In the invention configured as described above, when the overvoltage protection function of the IC detects an overvoltage, it shifts to a latch mode in which the stop is not released until the power supply is cut off. Oscillation resumes only after it has been reliably shut off. Therefore, the IC can be reliably protected from overvoltage.

Further, as an example of a specific configuration for solving the above-described problem, the invention according to claim 1 is that the DC power supplied from the main power supply circuit is converted into AC by the resonance circuit, and then the plasma is generated by the signal generation unit. In a plasma display device having a driving power supply circuit for generating a driving signal for driving a panel,
When the resonance circuit detects an overvoltage state of a start signal input from a microcomputer to start resonance, the resonance circuit shifts to a latch mode and stops oscillation, and an oscillation duty by feedback. An IC having a feedback terminal for controlling the ratio, a start signal from the microcomputer is received and output to the input terminal of the IC, and a first feedback signal supplied from the signal generator via a photocoupler is fed back to the IC. A resonance drive unit that outputs to a terminal, a plurality of transistors and a Zener diode, and a second output from the signal generation unit via a feedback transformer when the signal generation unit is in an overvoltage state. The Zener diode is broken down by the feedback signal. An overvoltage signal is generated and output to the input terminal to differentiate the overvoltage protection function of the IC and shift to the latch mode, thereby stopping the generation of the driving signal of the driving power supply circuit. And a supply unit.

As described above, according to the present invention, in an IC having an overvoltage protection function for accepting a signal for starting oscillation from an input terminal and detecting an overvoltage state of the input signal to stop oscillation, It is possible to detect an abnormality of the start signal at the terminal and an overvoltage state of the secondary side circuit to perform IC overvoltage protection.
According to the invention of claim 3, since the overvoltage signal is generated using the feedback signal, the circuit configuration can be simplified without requiring a signal generation source.
According to the invention of claim 4, the IC can be reliably protected from overvoltage. Is possible.
Furthermore, it is needless to say that in a more specific configuration as in claim 1, the same effects as in the inventions of claims 2 to 4 described above can be obtained.

  As a specific description of the power supply circuit of the present invention, a plasma display device using the power supply circuit will be described. However, the power supply circuit of the present invention is not limited to the one used for the plasma display device, and can be applied as long as the power supply circuit of the present invention is used.

Hereinafter, embodiments of the present invention will be described in the following order.
(1) Embodiment (1-1) Configuration of Plasma Display Device (1-2) Configuration of Driving Power Supply Circuit (1-3) Configuration of Resonant Circuit (1-4) Overvoltage Protection Method (2) Embodiment summary of

(1) Embodiment (1-1) Configuration of Plasma Display Device A first embodiment of a plasma display device according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram illustrating a plasma display apparatus 600 according to the present invention. The plasma display apparatus 600 is for displaying an image by causing a screen to emit plasma based on an input image signal. Therefore, the plasma display device 600 includes a plasma panel 200 that displays an image by plasma emission, a drive power supply circuit 100 for driving the plasma panel 200, and a main power supply circuit 300 that supplies power to the drive power supply circuit 100. A signal input terminal 400 that receives a video signal and outputs it to the driving power supply circuit 100, and a microcomputer 500 that controls each element described above.

  With the configuration of the plasma display apparatus 600 described above, when a video signal is supplied from the signal input terminal 400 to the drive power supply circuit 100, the drive power supply circuit 100 generates a drive signal for causing the plasma display apparatus 600 to emit light. The drive signal generated by the drive power supply circuit 100 is generated from the stabilized power supply generated by the main power supply circuit 300 based on the commercial power supply, and further from the video signal input from the signal input terminal 400. The drive power supply circuit 100 is for applying Vsus, Vset, Vscan, Ve, and Vadd, which are drive signals for driving the plasma panel 200, to each electrode of the plasma panel 200. Therefore, the drive power supply circuit 100 includes a Vsus drive circuit 10, a Vset drive circuit 20, a Vscan drive circuit 30, a Ve drive circuit 40, and a Vadd drive circuit 50 drive circuit. The driving signals thus applied are applied to the plasma panel 200 in a predetermined order.

  The flow of driving the plasma panel 200 will be described below. The driving of the plasma panel 200 includes an initialization period in which a voltage applied to each pixel constituting the plasma panel 200 is discharged and reset, a set period in which preparation for driving the plasma panel 200 is performed, and an address period in which pixels to emit light are specified. In addition, it is composed of a sustain period for maintaining the light emission of the pixel. Since the specific configuration of the plasma panel 200 is a well-known technique, a description thereof will be omitted here. The driving power supply circuit 100 applies a predetermined driving signal to the plasma panel 200 during each of the above-described periods. The microcomputer 500 outputs a start signal for each drive circuit to output a drive signal. Thereby, the microcomputer 500 constitutes a start signal transmission unit that controls timing.

  Specifically, Ve, which is a driving signal, is output from the Ve driving circuit 40 during the initialization period, and light emission of each pixel of the plasma panel 200 is stopped. Next, in the set period, Vset, which is a drive signal, is applied to the set electrode of the plasma panel 200 from the Vset drive circuit 20 to prepare for light emission. Further, in the address period, Vadd which is a drive signal from the Vadd drive circuit 50 and Vscan which is a drive signal from the Vscan drive circuit 30 are applied to the address electrode and the scan electrode of the plasma panel 200, thereby specifying the pixel to emit light. Made. Finally, Vsus, which is a drive signal, is applied from the Vsus drive circuit 10 to the sustain electrode of the plasma panel 200, and light emission is maintained. The above-described flow is repeated in the microcomputer 500, whereby the plasma display apparatus 600 causes specific pixels to emit light and displays an image on the plasma panel 200.

(1-2) Configuration of Driving Power Supply Circuit Next, a specific configuration of the driving power supply circuit 100 will be described. As described above, the drive power supply circuit 100 includes the Vsus drive circuit 10, the Vset drive circuit 20, the Vscan drive circuit 30, the Ve drive circuit 40, and the Vadd drive circuit 50, and the above-described series under the control of the microcomputer 500. Execute the drive. Since the configuration of each drive circuit is substantially the same, the specific configuration will be described below with a focus on the Vsus drive circuit 10.

  FIG. 2 is a diagram illustrating a circuit diagram centered on the Vsus drive circuit 10. From the figure, the Vsus drive circuit 10 includes a resonance circuit 11 that converts the 385 volt DC power output from the main power supply circuit 300 into AC, and a main transformer 12 that outputs the AC power generated by the resonance circuit 11 by induction. And a signal generation unit 13 that generates Vsus, which is a drive signal, based on the power supply from the main transformer 12. Further, the IC 11 a of the resonance circuit 11 is connected to the microcomputer 500 and is connected to the signal generator 13, the feedback transformer 14, and the photocoupler 15. With the above-described configuration, the Vsus drive circuit 10 is largely configured so that when the start signal is output from the microcomputer 500 to the IC 11, the DC power output from the main power supply circuit 300 is converted into AC by the resonance circuit 11 and is converted from the main transformer 12. Mainly on the signal generator 13. Thereafter, the signal generator 13 generates Vsus based on the AC power input via the main transformer 12 and outputs the Vsus to the plasma panel 200.

(1-3) Configuration of Resonant Circuit A specific configuration of the resonant circuit of the present invention will be described below. FIG. 3 is a block diagram showing the internal logic of the IC 11a in the embodiment of the present invention. As described above, the resonance circuit 11 includes the IC 11a serving as a control center and the resonance drive unit 11b configured by elements. Further, the IC 11a performs constant voltage control and overcurrent based on the input terminal 11a1 that starts the oscillation upon receiving the start signal from the microcomputer 500, and the feedback signal input from the signal generator 13 via the feedback transformer 14. The configuration includes a feedback terminal 11a2, a source terminal 11a3, a drain terminal 11a4, and a ground terminal 11a5. Since the resonance circuit 11 is a well-known technique, a detailed description thereof is omitted. However, in general, when a start signal is input from the microcomputer 500 to the input terminal 11a1, the start signal is output from the internal start block 11a6 to the driver block 11a8. The oscillation of the frequency generation circuit 11a9 is started. At this time, the start block 11a6 is connected in parallel with the overvoltage protection block 11a7 and monitors the state of the start signal. Next, the oscillation between the source terminal 11a3 and the drain terminal 11a4 is caused by the oscillation of the frequency generation circuit 11a9. And the alternating current is generated in the primary coil 12a of the main transformer 12. Thus, a current flows through the secondary coil 12b of the main transformer 12 by induction, and the signal generator 13 generates Vsus. Further, Vsus generated by the signal generation unit 13 is output to the feedback terminal 11a2 of the IC 11a through the feedback transformer 14. The feedback signal input via the feedback terminal 11a2 controls the oscillation of the frequency generation circuit 11a9 and switches the duty ratio of the AC power supply applied to the main transformer 12. In this way, the generation and control of the alternating current is performed by the IC 11a and the resonance driver 11b.

  With the above-described configuration, in the normal state, the first feedback signal is output to the feedback terminal 11a2 of the IC 11a by the photocoupler 15 via the resonance driving unit 11b based on the voltage value of Vsus generated by the signal generation unit 13. Thus, the duty ratio of the voltage applied to the main transformer 12 is controlled in the IC 11a. Further, in the overcurrent state of Vsus generated by the signal generation unit 13, an overcurrent detection signal is output to the feedback terminal 11a2 via the photocoupler 15. As a result, the overcurrent protection of the IC 11a is performed by controlling the duty ratio of oscillation.

(1-4) Overvoltage Protection Method The overcurrent protection method for the IC 11a configured as described above does not protect the IC 11a against an overvoltage state. In addition, it takes time to stop the oscillation of the IC 11a and the feedback terminal 11a2 does not shift to the latch mode, so that the IC 11a is not reliably protected. Therefore, in the embodiment of the present invention, an overvoltage signal supply unit that generates an overvoltage signal from the feedback signal from the signal generation unit 13 and outputs it to the IC 11a is added to the resonance driving unit 11b, so that the signal generation unit 13 is in an overvoltage state. At this time, an overvoltage signal is generated from the second feedback signal generated by the signal generator 13, and the overvoltage signal is output to the input terminal 11a1 of the IC 11a. As a result, the overvoltage protection block 11a7 is differentially shifted in the IC 11a and shifts to the latch mode.

  The configuration of the overvoltage signal supply unit 11c and the signal flow will be described below. FIG. 4 is a circuit diagram showing the flow of the second feedback signal in the normal state. FIG. 5 is a circuit diagram showing the flow of a feedback signal in an overvoltage state. The overvoltage signal supply unit 11c includes a Zener diode 11c1, transistors 11c3 and 11c6, and further resistors 11c2, 11c4, and 11c5. The overvoltage signal is supplied only when the signal output from the feedback transformer breaks down the Zener diode 11c1. Is output to the input terminal 11a1 of the IC 11a. At this time, the value of the Zener diode 11c1 is appropriately designed according to the overvoltage state that the user wants to set. As shown in FIG. 4, when the signal generator 13 is not in an overvoltage state, the signal flowing to the resonance driver 11b via the feedback transformer 14 is blocked by the Zener diode 11c1, and the signal is output to the input terminal 11a1 of the IC 11a. Not.

  Next, a signal flow in an overvoltage state will be described with reference to FIG. When the signal generation unit 13 is in an overvoltage state, a signal flowing to the resonance driving unit 11b via the feedback transformer 14 breaks down the Zener diode 11c1 and generates an overvoltage signal by a breakdown current. Further, an overvoltage signal is supplied to the base of the transistor 11c6. As a result, the collector / emitter of the transistor 11c6 communicates with each other, and a signal flows through the resistor 11c4 due to branching. For this reason, a signal flows through the base of the transistor 11c3, causing the collector / emitter of the transistor 11c3 to communicate with each other, and an overvoltage signal is output to the input terminal 11a1 of the IC 11a. At this time, the overvoltage signal flowing through the input terminal 11a1 of the IC 11a has a high voltage because the signal generator 13 is in an overvoltage state, and the overvoltage protection block 11a7 of the IC 11a stops oscillation and shifts to the latch mode. The value of the overvoltage signal input to the IC 11a described above is a value determined based on the overvoltage detection function of the IC 11a.

(2) Summary of Embodiments As described above, the IC 11a having an overvoltage protection function for receiving a signal for starting oscillation from the input terminal 11a1 and detecting an overvoltage state of the input signal to stop oscillation. In the Vsus drive circuit 10 using the signal, the overvoltage state of the signal generation unit 13 is output to the resonance drive unit 11b through the feedback transformer 14, and the overvoltage signal is input to the input terminal 11a1 by the overvoltage signal supply unit 11c to generate the IC 11a. Stops oscillation and performs overvoltage protection. Therefore, it is possible to detect the overvoltage state of the microcomputer 500 and the signal generation unit 13 with a single input terminal and perform IC overvoltage protection.

Needless to say, the present invention is not limited to the above embodiments. It goes without saying for those skilled in the art,
・ Applying mutually interchangeable members and configurations disclosed in the above embodiments by appropriately changing the combination thereof.− Although not disclosed in the above embodiments, it is a publicly known technique and the above embodiments. The members and configurations that can be mutually replaced with the members and configurations disclosed in the above are appropriately replaced, and the combination is changed and applied. It is an embodiment of the present invention that a person skilled in the art can appropriately replace the members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments, and change the combinations and apply them. It is disclosed as.

It is a block block diagram showing the plasma display apparatus of this invention. It is a figure showing the circuit diagram centering on a Vsus drive circuit. It is a block block diagram showing the internal logic of IC in embodiment of this invention. It is a circuit diagram showing the flow of the 2nd feedback signal in normal time. It is a circuit diagram showing the flow of the feedback signal in an overvoltage state. It is a figure showing the internal logic of IC which has an overvoltage detection function in the start terminal which receives the signal for performing an oscillation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Vsus drive circuit, 11 ... Resonance circuit, 11a ... IC, 11a1 ... Input terminal, 11a2 ... Feedback terminal, 11a3 ... Source terminal, 11a4 ... Drain terminal, 11a5 ... Ground terminal, 11a6 ... Start block, 11a7 ... Overvoltage protection block 11a8: Driver block, 11a9: Frequency generation circuit, 11b: Resonance drive unit, 11c ... Overvoltage signal supply unit, 11c1 ... Zener diode, 11c2 ... Resistance, 11c3 ... Transistor, 11c4, 11c5 ... Resistance, 11c6 ... Transistor, 12 ... Main transformer, 12a ... primary coil, 12b ... secondary coil, 13 ... signal generator, 14 ... feedback transformer, 15 ... photocoupler, 20 ... Vset drive circuit, 30 ... Vscan drive circuit, 40 ... Ve drive circuit, 50 ... V dd driving circuit, 100 ... drive power circuit, 200 ... plasma panel, 300 ... main power circuit, 400 ... signal input terminal, 500 ... microcomputer, 600 ... plasma display device

Claims (4)

A drive power supply circuit that generates a drive signal for driving a plasma panel in a signal generation unit based on the generated AC power supply after converting the DC power supplied from the main power supply circuit into AC by a resonance circuit In a plasma display device having
When the resonance circuit detects an overvoltage state of a start signal input from a microcomputer to start resonance, the resonance circuit shifts to a latch mode and stops oscillation, and an oscillation duty by feedback. An IC having a feedback terminal for controlling the ratio;
A resonance drive unit that receives a start signal from the microcomputer and outputs the start signal to the input terminal of the IC, and outputs a first feedback signal supplied from the signal generation unit via a photocoupler to the feedback terminal;
The zener diode is configured based on a plurality of transistors and a zener diode, and when the signal generator is in an overvoltage state, the zener diode is broken down by a second feedback signal output from the signal generator via a feedback transformer. The overvoltage signal is generated and output to the input terminal to differentiate the overvoltage protection function of the IC and shift to the latch mode, thereby stopping the generation of the driving signal of the driving power supply circuit. A plasma display device comprising a signal supply unit. An IC having an overvoltage protection function for receiving a signal for starting oscillation and detecting an overvoltage state of the input signal to stop the oscillation;
A start signal transmitter for supplying a start signal for oscillating the IC to the input terminal;
In a power supply circuit having a secondary side circuit that generates a predetermined voltage based on the oscillation of the IC,
An overvoltage signal supply unit that outputs an overvoltage signal to the input terminal of the IC by feedback when the secondary side circuit is in an overvoltage state, and that makes the overvoltage protection function of the IC differential. Power supply circuit. The IC is built in a resonance circuit that converts a DC power source on the primary side into AC by resonance,
The AC power converted by the resonance circuit is configured to be supplied to the secondary circuit via a transformer,
The overvoltage signal supply unit is incorporated in the resonance circuit and generates the overvoltage signal based on a voltage value of a feedback signal output from a secondary circuit via a feedback transformer. Power supply circuit.   4. The power supply according to claim 2, wherein the IC has an overvoltage protection function for shifting to a latch mode and stopping oscillation when an overvoltage signal having a predetermined voltage is output. circuit.

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