JP4290925B2 - Overvoltage protection circuit and switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an overvoltage protection circuit and a switching power supply, and more particularly to an overvoltage protection circuit and a switching power supply having a function of latching and stopping a switching operation when an overvoltage occurs.
[0002]
[Prior art]
A switching power supply is a stabilized power supply incorporating a switching voltage stabilizing circuit. That is, the switching power supply has a function of supplying a stable DC voltage to the device (load) even when the input voltage varies.
When any abnormality occurs in this switching power supply, it is common to stop the switching operation by operating an overvoltage protection circuit in order to ensure the safety of the device (load).
[0003]
FIG. 5 shows a circuit configuration of such a conventional general switching power supply.
As shown in the figure, the switching power supply 1 turns on / off the main transistor 43 based on the output constant voltage control means 10 for detecting the voltage value on the output side and the signal from the output constant voltage control means 10. And switching control means 20 for adjusting the output voltage.
[0004]
Further, the switching power supply 1 includes, as a protection circuit 30, an overvoltage detection unit 31 that detects an output overvoltage, an overcurrent detection unit 32 that detects an overcurrent, and a signal from the overvoltage detection unit 31 or the overcurrent detection unit 32. Based on this, latch stop means 33 for stopping the switching operation is provided.
[0005]
A more specific circuit configuration of the conventional switching power supply is shown in FIG.
In the switching power supply 1 shown in the figure, an overvoltage detecting means 50 detects an output overvoltage and outputs a current, a Zener diode 51 that divides the output overvoltage to protect the Zener diode 51 and the like, and an output overvoltage. And a photothyristor (light emitting side) 53 that receives and emits light.
[0006]
Further, the latch stop means 60 shown in the figure receives the light (detection signal) from the photothyristor (light emitting side) 53 and outputs a current, and the gate and source of the main transistor 82. And a transistor 62 for turning off the main transistor 83, and a resistor 63 and a capacitor 64 for applying a voltage to the gate of the transistor 62 based on a current from a photothyristor (light receiving side) 61. .
These overvoltage detection means 50 and latch stop means 60 correspond to the protection circuit 30 in FIG.
[0007]
In the switching power supply 1 having such a configuration, when an output overvoltage occurs, the Zener diode 51 outputs a current based on the generated overvoltage, and the photothyristor (light emitting side) 53 emits a detection signal. Upon receipt of this detection signal, the photothyristor (light receiving side) 61 outputs a control current, and based on this control current, the transistor 62 turns off the main transistor 82 to stop the switching operation.
By such an operation, the switching power supply 1 prevents the generated output overvoltage from being applied to the load 200 and protects the load 200 safely.
[0008]
The switching power supply 1 shown in FIG. 5 is a block diagram illustrating a general protection function, whereas the switching power supply 1 shown in FIG. 6 includes a protection circuit using a specific electronic element. The structure of the switching power supply 1 is illustrated. Depending on the electronic element and its configuration, one electronic element (or one electronic circuit) may have two or more functions.
For these reasons, the circuit configurations of the switching power supply shown in FIG. 5 and the switching power supply shown in FIG. 6 are not necessarily matched.
[0009]
Further, for example, although the overcurrent detection means 12 shown in FIG. 5 is not shown in FIG. 6, it is of course possible to detect the overcurrent by providing the overcurrent detection means in the switching power supply of FIG. In this case, the latch stop means 60 stops the switching operation based on the detection signal from the overcurrent detection means.
[0010]
Incidentally, the latch stop means of the switching power supply is generally used not only in the overvoltage protection circuit but also in other protection circuits.
For this reason, as shown in FIG. 7, a delay time A is provided between the occurrence of the output overvoltage ((1) in the figure) and the latch stop of the switching operation ((2) in the same figure). Further, a mask time A for the latch stop means is secured in order to prevent a problem that the power supply is frequently stopped due to a hypersensitive reaction.
[0011]
[Problems to be solved by the invention]
However, in the conventional overvoltage protection circuit, as shown in FIG. 7, the output voltage suddenly increases within a short time of the secured delay time (or mask time). This phenomenon was due to an overvoltage caused by some abnormality occurring in the switching power supply.
The increased voltage in the delay time or the like has been one of the causes for damaging the device (load).
[0012]
The overvoltage protection circuit is originally provided in the switching power supply in order to protect the device (load) from the output overvoltage. Nevertheless, securing the delay time and mask time necessary to prevent hypersensitivity reactions, etc., on the contrary, increased the possibility of damage to the equipment (load) due to output overvoltage.
However, if the masking time was secured to an appropriate length, malfunctions were reduced and the reliability of the switching power supply could be improved.
[0013]
The present invention has been considered in view of the above circumstances, and can suppress latching of the switching operation while suppressing the overvoltage in the delay time and the like to safely protect the device (load), and the reliability of the switching power supply. It is an object to provide an overvoltage protection circuit and a switching power supply capable of maintaining and improving the above.
[0014]
[Means for Solving the Problems]
  In order to achieve this object, an overvoltage protection circuit according to claim 1 of the present invention detects the occurrence of an overvoltage.And output detection signalAn overvoltage protection circuit having an overvoltage detection means and a latch stop means for stopping a switching operation based on a detection signal from the overvoltage detection means, from when an overvoltage occurs until the switching operation stops A delay time voltage control means for controlling the switching operation in the delay time based on a detection signal from the overvoltage detection means, the overvoltage detection means has a signal sending unit for outputting a detection signal, The delay voltage control means has a switching control unit that clamps the output voltage of the overvoltage protection circuit by repeatedly connecting and disconnecting the switching element based on the detection signal from the signal transmission unit. Is on the light emitting side of the photocoupler, and the switching control unit is on the light receiving side of the photocoupler. Switching element is composed of a field effect transistor, one terminal having a light receiving side of the photocoupler is connected to the base of the field effect transistor and the other terminal, connected to the source of the field effect transistorWhen the light emission side of the photocoupler emits light due to the occurrence of an overvoltage, the light reception side of the photocoupler is turned on, the field effect transistor is turned off, the supply of the output voltage to the load is temporarily stopped, and the output voltage is lowered. When the overvoltage detection state is canceled and the light emission side of the photocoupler stops light emission due to this cancellation, the field effect transistor is turned on, the supply of the output voltage to the load is resumed, the output voltage rises, and the overvoltage detection state is resumed. The light-emitting side of the photocoupler emits light, the light-receiving side of the photocoupler turns on, the field effect transistor turns off, and this operation continues until the switching operation stops, so that the output voltage repeatedly decreases and rises near the specified voltage. ClampedAs a configuration.
[0015]
When the overvoltage protection circuit is configured in this way, the output voltage clamp function (the overvoltage protection circuit controls the switching operation based on the detection signal from the overvoltage detection means until the switching operation stops after the overvoltage occurs. Therefore, the load device can be protected more safely and the operation of the power supply circuit can be stopped.
[0016]
That is, since the overvoltage from the generation of the output overvoltage to the latch stop (delay time or mask time) can be clamped by the operation control of the switching element in the delay time voltage control means, the overvoltage is not applied to the load. Therefore, the switching operation of the power supply circuit can be stopped while protecting the load safely.
[0017]
Furthermore, since the output voltage at the mask time is no longer an overvoltage, the mask time can be increased safely.
Therefore, it is possible to prevent a temporary malfunction, and to maintain and improve the reliability of the power supply system.
[0018]
  If the overvoltage protection circuit has such a configuration, when the output voltage of the power supply rises abnormally for some reason, a detection signal is output from the overvoltage detection unit, and based on this detection unit, the signal transmission unit to the switching control unit Since the control signal is sent and the switching control unit controls the operation of the switching element, the overvoltage during the delay time can be clamped to prevent the load from being damaged.
[0019]
  Therefore, such an output voltage clamping function can stop the operation of the power supply circuit while the load is safely protected.
[0020]
  In addition, since the signal sending unit is composed of the light emitting side of the photocoupler and the switching control unit is composed of the light receiving side of the photocoupler, the photocoupler issuance side and light receiving side immediately respond to the operation of the switching element. Since the control signal (transmitted / received light) is emitted and received, the output overvoltage within the delay time when the latch is stopped can be clamp controlled.
[0021]
  In addition, the switching element is composed of a field effect transistor, and one terminal on the light receiving side of the photocoupler is connected to the base of the field effect transistor, and the other terminal is connected to the source of the field effect transistor. Therefore, when the light receiving element of the photocoupler receives a control signal, the base and the source of the switching element are short-circuited, so that the switching element can be turned off. Further, when the light receiving element of the photocoupler is not receiving a control signal, the base and source of the switching element are not short-circuited, so that the switching element can be turned on.
[0022]
  In this way, the operation of the switching element can be controlled by the operation of the photocoupler that constitutes the clamp control unit, so overvoltage during delay time etc. is suppressed, and the switching operation is latched while protecting the device (load) safely. Can be stopped.
[0023]
  According to a second aspect of the present invention, the switching power supply includes the overvoltage protection circuit according to the first aspect.
  If the switching power supply has such a configuration, even if some abnormalities occur and an output overvoltage occurs, the switching power supply uses an overvoltage protection circuit that it has to suppress overvoltage in delay time, etc. The switching operation can be latched and stopped while the device (load) is safely protected.
[0024]
  In place of the delay time voltage control means, the PWM control means for controlling the duty of the on / off pulse in the switching element based on the detection signal from the overvoltage detection means until the switching operation is stopped after the overvoltage is generated. It can also be set as the structure which has.
  When the overvoltage protection circuit has such a configuration, the PWM control unit controls the duty of the on / off pulse in the switching element based on the detection signal from the overvoltage detection unit, and suppresses the output power when the overvoltage occurs. it can. For this reason, a power supply can be stopped, protecting a load (apparatus) safely.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
First, a first embodiment of an overvoltage protection circuit and a switching power supply according to the present invention will be described with reference to FIG.
This figure is an electric circuit diagram showing the configuration of the switching power supply of the present embodiment.
[0026]
As shown in the figure, the switching power supply 1 includes an output constant voltage control means 10, a switching control means 20, a protection circuit 30, a rectifying bridge diode 41, a smoothing capacitor 42, a main transistor 43, a transformer. 44, diodes 45 and 46, a choke coil 47, and a smoothing capacitor 48, which rectifies an AC voltage from the input source 100 and supplies a DC constant voltage to the load 200.
[0027]
Here, the output constant voltage control means 10 detects the voltage value on the output side.
Based on the signal from the output constant voltage control means 10, the switching control means 20 adjusts the output voltage by turning on / off the main transistor 43.
The protection circuit 30 is a circuit having a function of detecting an overvoltage or overcurrent and stopping the switching operation. The protection circuit 30 includes an overvoltage detection unit 31, an overcurrent detection unit 32, a latch stop unit 33, and a delay time voltage control unit. 34.
[0028]
When the overvoltage detection means 31 detects the output overvoltage, it sends a detection signal to the latch stop means 33. When the overcurrent detection unit 32 detects an overcurrent, the overcurrent detection unit 32 sends a detection signal to the latch stop unit 33.
The latch stop means 33 latches and stops the switching operation based on the detection signal from the overvoltage detection means 31 or the overcurrent detection means 32.
[0029]
Based on the detection signal from the overvoltage detection means 31, the delay time voltage control means 34 performs switching control from the generation of this detection signal (output overvoltage generation) to the latch stop of the switching operation (delay time or mask time). The means 20 is controlled to suppress the output overvoltage.
Note that the protection circuit 30 is a circuit having a function of detecting an overvoltage or an overcurrent and stopping the switching operation, and thus has a function as an overvoltage protection circuit. That is, the overvoltage protection circuit of the present embodiment can be configured to include the overvoltage detection means 31, the latch stop means 33, and the delay time voltage control means 34.
[0030]
Next, the operation of the switching power supply shown in FIG. 1 will be described.
The AC voltage from the input source 100 is rectified to a DC voltage by the rectifying bridge diode 41, and the DC voltage is smoothed by the smoothing capacitor 42 and transformed by the transformer 44.
The secondary voltage of the transformer 44 is further smoothed by the smoothing capacitor 48, converted to a constant voltage value by the output constant voltage control means 10, and supplied to the load 200.
[0031]
While the output voltage is supplied to the load 200, the overvoltage detection means 31 detects whether or not the output voltage is an overvoltage. Further, the overcurrent detection means 32 detects whether or not the output current is an overcurrent.
When an overvoltage or overcurrent is detected in these detection circuits 31 and 32, a detection signal is sent to the latch stop means 33.
[0032]
In the latch stop means 33, the switching operation in the switching control means 20 is latched and stopped based on the input detection signal. That is, the transistor 43 that is a switching element is turned off under the control of the switching control means 20, the voltage to the primary side of the transformer 44 is stopped, and the supply of the DC voltage to the load 200 is stopped.
However, since a delay time (mask time) is provided, a time lag occurs between the time when the detection signal is generated and the time when the switching operation is stopped.
[0033]
Further, the detection signal from the overvoltage detection means 31 is sent to the delay voltage control means 34.
In the delay time voltage control means 34, the switching control means 20 is controlled during the delay time (or mask time) based on the input detection signal to suppress the output overvoltage.
For this reason, since the overvoltage during the delay time is clamped, the switching operation can be latched and stopped while the load is safely protected.
[0034]
Next, a specific circuit configuration example of the switching power supply will be described with reference to FIG.
As shown in the figure, the switching power supply 1 includes an overvoltage detection means 50, a latch stop means 60, a switching control means 70, a smoothing capacitor 81, a main transistor (switching element) 82, a resistor 83, a transformer 84, a transistor 85, a smoothing capacitor 86, and a delay time voltage control means 90. The DC voltage from the DC input source 300 is converted to a constant voltage and supplied to the load 200.
[0035]
The overvoltage detection means 50 detects the output overvoltage and outputs a current, a resistor 52 that divides the output overvoltage to protect the Zener diode 51 and the like, and a signal transmission that receives the output overvoltage and outputs a detection signal Part 53. The signal sending unit 53 includes a photothyristor (light emission side) 53-1 that sends a detection signal to the latch stop means 60, and a photocoupler (light emission side) 53-2 that sends the detection signal to the delay time voltage control means 90. ing.
[0036]
The latch stop means 60 short-circuits the photothyristor (light receiving side) 61 that receives light (detection signal) from the photothyristor (light emitting side) 53-1 and outputs a current, and the gate and source of the main transistor 82. Thus, the transistor 62 for turning off the main transistor 82, the resistor 63 and the capacitor 64 for applying a voltage to the gate of the transistor 62 based on the current from the photothyristor (light receiving side) 61, the capacitor 65, and the resistors 66 and 67 And have.
[0037]
The switching control means 70 includes a transistor 71, capacitors 72 and 73, and resistors 74 and 75, and has a configuration in which a self-excited converter is formed by RCC synchronous rectification.
As the main transistor (switching element) 82, a field effect transistor (FET) can be used.
[0038]
The delay time voltage control means 90 includes a photocoupler (light receiving side, switching control unit) 91.
When the photocoupler (light receiving side) 91 receives the detection signal from the photocoupler (light emitting side) 53-2, the gate and the source of the main transistor 82 are short-circuited to turn off the main transistor 82.
The overvoltage detection means 50, the latch stop means 60, and the delay voltage control means 90 correspond to the protection circuit 30 shown in FIG.
[0039]
The switching power supply 1 shown in FIG. 1 is a block diagram of the overvoltage protection function using the delay time voltage control means 34, whereas the switching power supply 1 shown in FIG. 2 shows the configuration of the switching power supply 1 including the delay time voltage control means 90 assembled in the above. Depending on the electronic element and its configuration, one electronic element (or one electronic circuit) may have two or more functions.
For these reasons, the circuit configurations of the switching power supply shown in FIG. 1 and the switching power supply shown in FIG. 2 do not always match.
[0040]
Further, for example, the overcurrent detection means 32 shown in FIG. 1 is not shown in FIG. 2, but it is of course possible to detect the overcurrent by providing the overcurrent detection means in the switching power supply 1 of FIG. In this case, the latch stop means 60 stops the switching operation based on the detection signal from the overcurrent detection means.
[0041]
Further, when the delay time voltage control means 34 shown in FIG. 1 receives the detection signal, it controls the switching control means 20 to turn the main transistor 43 on / off, whereas the delay time control means 34 shown in FIG. The hour voltage control unit 90 directly causes the main transistor 82 to perform an ON / OFF operation without using the switching control unit 20.
However, depending on the circuit configuration, for example, the photocoupler (light receiving side) 91 can control the transistor 71 to turn the main transistor 82 on and off.
[0042]
Next, the operation of the switching power supply shown in FIG. 2 will be described.
An output voltage higher than the sum of the Zener voltage of the Zener diode 51, the forward voltage of the photothyristor (light emitting side) 53-1, and the forward voltage of the photocoupler (light emitting side) 53-2 is generated due to some abnormality. Then, the photothyristor (light emission side) 53-1 and the photocoupler (light emission side) 53-2 emit light.
[0043]
Among these, the photothyristor (light-emitting side) 53-1 emits light, so that the photothyristor (light-receiving side) 61 of the latch stop means 60 is continuously turned on with one pulse.
Then, based on the current from the photothyristor (light receiving side) 61, the transistor 62 is turned on, the gate and source of the main transistor 82 are short-circuited, the main transistor 82 is turned off, and the power supply is latched and stopped.
[0044]
However, since a delay time (mask time) is provided between the time when the photothyristor (light emitting side) 53-1 emits light (overvoltage is generated) and the switching operation is stopped, a time lag occurs. Yes.
In this delay time (or mask time), an operation based on light emission of the photocoupler (light emission side) 53-2 is performed.
[0045]
When the photocoupler (light emitting side) 53-2 emits light, the photocoupler (light receiving side) 91 is turned on, the main transistor 82 is turned off, and supply of the output voltage to the load 200 is temporarily stopped. . As a result, the output voltage decreases. Thereby, since the overvoltage detection state is canceled, the photocoupler (light emission side) 53-2 stops light emission. Then, the main transistor 82 is turned on again, and supply of the output voltage to the load 200 is resumed. Then, since the output voltage again becomes an overvoltage state, the photocoupler (light emission side) 53-2 is turned on to emit light.
[0046]
When such an operation is repeated, the output voltage is eventually clamped as shown in FIG.
This operation continues until the latch stop means 60 operates to stop the power supply latch. For this reason, since no overvoltage is applied to the load 200, the load 200 can be protected from the overvoltage.
[0047]
3 is a voltage value obtained by summing the Zener voltage of the Zener diode 51, the forward voltage of the photothyristor (light emitting side) 53-1, and the forward voltage of the photocoupler (light emitting side) 53-2. Will come to show.
Also, (1) in the figure indicates when an overvoltage occurs, and (2) indicates when the switching operation is stopped (when the switching element is OFF or when the power supply latch is stopped).
[0048]
[Second Embodiment]
Next, a second embodiment of the overvoltage protection circuit and the switching power supply according to the present invention will be described with reference to FIG.
This figure is an electric circuit diagram showing a circuit configuration of the switching power supply of the present embodiment.
[0049]
This embodiment differs from the first embodiment in the configuration of the switching control means and the overvoltage detection means. That is, in the first embodiment, the switching control means is self-excited and the voltage control means at the time of delay is provided in the protection circuit, whereas in this embodiment, the switching control means is composed of the PWM control means, and overvoltage protection is provided. The circuit overvoltage detection means or the like is configured to send a detection signal to the PWM control means. Other components are the same as those in the first embodiment.
Therefore, in FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0050]
As shown in FIG. 4, the switching power supply 1 includes a PWM (Pulse-width modulation) control unit 20 a as the switching control unit 20.
Here, the PWM control means 20a controls the duty of the on / off pulse in the switching element. In particular, the PWM control unit 20a controls the duty of the on / off pulse in the switching element based on the detection signal from the overvoltage detection unit until the switching operation is stopped after the overvoltage is generated.
[0051]
The protection circuit 30 includes an overvoltage detection unit 31, an overcurrent detection unit 32, a latch stop unit 33, and (a part of) the PWM control unit 20a.
The overvoltage detection means 31 sends a detection signal to the latch stop means 33 and the PWM control means 20a. That is, the detection signal sent from the overvoltage detection means 31 is shared and sent to the latch stop means 33 and the switching control means 20.
[0052]
The PWM control means 20a (part of) included in the protection circuit 30 is a function of clamping the output overvoltage in the delay time (or mask time) among the functions of the PWM control means 20a (that is, an overvoltage is generated). The function of controlling the duty of the on / off pulse in the switching element based on the detection signal from the overvoltage detection means until the switching operation stops. The other functions (that is, the function of controlling the duty of the on / off pulse in the switching element in the normal switching operation) function as the switching control means 20 that operates based on the signal from the output constant voltage control means 10.
[0053]
Note that the protection circuit 30 is a circuit having a function of detecting an overvoltage or an overcurrent and stopping the switching operation, and thus has a function as an overvoltage protection circuit. That is, the overvoltage protection circuit of the present embodiment can be configured to include the overvoltage detection unit 31, the latch stop unit 33, and the PWM control unit 20a (a part thereof).
[0054]
In the case of the switching power supply 1 shown in FIG. 2, the detection signal in the first embodiment is an optical signal transmitted and received by the photothyristors 53-1 and 61 or the photocouplers 53-2 and 91. The detection signal in the embodiment may be constituted by a current, a voltage, or the like as long as it is a signal for operating the PWM control means 20a.
[0055]
By adopting such a configuration of the switching power supply, the PWM control unit 20a having a function of reducing the duty can clamp the output overvoltage by reducing the output power particularly when the overvoltage is generated.
Further, the configuration of the present embodiment can be applied to any power source regardless of the power circuit method.
[0056]
【The invention's effect】
As described above, according to the present invention, even when the switching power supply is in an overvoltage state for some reason, the output overvoltage generated during the delay time of the latch stop means operation can be clamped. Therefore, it can be prevented from being damaged by the overvoltage, and the power supply can be safely stopped.
Further, since the output overvoltage is clamped and the load is protected, the mask time can be increased safely. For this reason, a transient malfunction can be prevented, and the reliability of the power supply system can be improved.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing a circuit configuration of a switching power supply according to a first embodiment of the present invention.
FIG. 2 is an electric circuit diagram showing a specific circuit configuration example of the switching power supply according to the first embodiment of the present invention.
FIG. 3 is a graph showing a change in output voltage clamped by the overvoltage protection circuit of the present invention.
FIG. 4 is an electric circuit diagram showing a circuit configuration of a switching power supply according to a second embodiment of the present invention.
FIG. 5 is an electric circuit diagram showing a circuit configuration of a conventional switching power supply.
FIG. 6 is an electric circuit diagram showing a specific circuit configuration example of a conventional switching power supply.
FIG. 7 is a graph showing a change in output voltage output from a conventional switching power supply.
[Explanation of symbols]
1 Switching power supply
10 Output constant voltage control means
20 Switching control means
20a PWM control means
30 Protection circuit
31 Overvoltage detection means
32 Overcurrent detection means
33 Latch stop means
34 Voltage control means during delay
41 Bridge diode for rectification
42 Smoothing capacitor
43 Main transistor
44 transformer
45 diodes
46 Diode
47 Choke coil
48 Smoothing capacitor
50 Overvoltage detection means
51 Zener diode
52 resistance
53 Signal transmitter
53-1 Photothyristor (light emission side)
53-2 Photocoupler (Light Emitting Side)
60 Latch stop means
61 Photothyristor (light receiving side)
62 Transistor
63 Resistance
64 capacitors
65 capacitors
66 Resistance
67 Resistance
70 Switching control means
71 transistor
72 capacitors
73 capacitor
74 Resistance
75 resistance
81 Smoothing capacitor
82 Main transistor
83 Resistance
84 transformer
85 transistors
86 Smoothing capacitor
90 delay voltage control means
91 Photocoupler (light receiving side, switching controller)
100 input source
200 load
300 DC input source

Claims (2)

Overvoltage detection means for outputting a detection signal upon detecting the occurrence of overvoltage;
Based on the detection signal from the over-voltage detecting means, a overvoltage protection circuit having a latch stop means for stopping the switching operation,
A delay time from the occurrence of the overvoltage until the switching operation is stopped,
Based on the detection signal from the overvoltage detection means, having a delay time voltage control means for controlling the switching operation in the delay time,
The overvoltage detection means has a signal sending unit that outputs the detection signal,
The delay time voltage control means has a switching control unit that clamps the output voltage of the overvoltage protection circuit by repeatedly connecting and disconnecting the switching element based on the detection signal from the signal sending unit,
The signal sending unit is composed of a light emitting side of a photocoupler,
The switching control unit consists of a light receiving side of the photocoupler,
The switching element comprises a field effect transistor;
One terminal on the light receiving side of the photocoupler is connected to the base of the field effect transistor, and the other terminal is connected to the source of the field effect transistor ,
When the light emitting side of the photocoupler emits light due to the occurrence of the overvoltage, the light receiving side of the photocoupler is turned on, the field effect transistor is turned off, and supply of the output voltage to the load is temporarily stopped, and the output voltage When the overvoltage detection state is canceled, and the light emission side of the photocoupler stops light emission, the field effect transistor is turned on, the supply of the output voltage to the load is resumed, and the output voltage rises. Then, an overvoltage detection state occurs again, the light emitting side of the photocoupler emits light, the light receiving side of the photocoupler is turned on, the field effect transistor is turned off,
By continuing this operation until the switching operation is stopped, the output voltage is clamped by repeatedly decreasing and increasing near a predetermined voltage . The overvoltage protection circuit according to claim 1 was provided.
A switching power supply characterized by that.

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