JP2003304686A - Switching power circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply which is of simple circuit configuration, consumes less power at standby, and produces less noise. <P>SOLUTION: The self-oscillation switching power supply is so constituted that a direct-current voltage is switched by a main switching element 37, connected with the primary winding 15 of a transformer 14; energy is transferred to a secondary winding 16; output voltage detection information from a feedback portion 39 is fed back to a switching control portion 38 which is coupled with the tertiary winding 17; and thereby turn-on/off the main switching element 37 is controlled. The switching element 37 comprises MOSFET. A drive signal line, connecting the gate of the switch element 37 and one end of the tertiary winding 17, is connected with the power supply side of the switching control portion 38. Thus, the energy for driving the switch element 37 is used as a control signal for the switching control portion 38. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit which is used while an input voltage is always applied or which is highly likely to be used, in a standby state (in a no-load state or a minute load state). The present invention relates to a switching power supply circuit capable of minimizing the self-consumed electric power and minimizing the waste of the consumed energy.

[0002]

2. Description of the Related Art The electric circuit diagram shown in FIG. 5 is an RCC (Ringing Choke Convertor) which has been widely used in the past.
It is an example of a switching power supply circuit of a system. AC power is generally rectified and input to the preceding stage of the input terminal 10 and the ground terminal 11 of this switching power supply circuit, but is not shown.

First, the primary side circuit with the transformer 14 as a boundary will be described. Input terminal 10 and ground terminal 11
A smoothing capacitor 23 is connected to a stage immediately after the capacitor, and the positive side of the smoothing capacitor 23 is connected to the primary winding 15 of the transformer 14, the collector of the main switch element 18 such as a dipole transistor, the emitter, the resistor 31, and the ground. The terminals 11 are sequentially connected in series. The input terminal 10 is connected to the base of the main switch element 18 and the collector of the control switch element 19 via a resistor 28. The emitter of the switch element 19 is connected to the ground terminal 11, and the base of the switch element 19 is a resistor 30.
It is connected to the emitter of the switch element 18 via.

The tertiary winding 17 of the transformer 14 as a voltage source has the same polarity as the primary winding 15, and one end thereof is
A resistor 29 and a capacitor 25 are sequentially connected in series to the base of the switch element 18, and the other end is connected to the ground terminal 11. The anode side of the diode 35 is connected to the connection point between the resistor 29 and the capacitor 25, and the cathode side of the diode 35 is connected to the base of the switch element 19 via the light receiving section 21 of the photocoupler. A capacitor 27 is connected between the cathode side of and the ground terminal 11. The diode 35, the capacitor 27, the light receiving section 21 of the photocoupler, and the switch element 19 constitute a switching control section 38. A snubber circuit including a diode 34, a resistor 32, and a capacitor 26 is connected in parallel with the primary winding 15 of the transformer 14.

Next, a secondary side circuit with the transformer 14 as a boundary will be described. Secondary winding 16 of the transformer 14
Has a polarity opposite to that of the primary winding 15, and a capacitor 24 is connected in parallel via a diode 33.
The positive side of is connected to one output terminal 12, and the negative side is connected to the ground terminal 13. further,
A feedback unit 39 including a light emitting unit 20 of the photocoupler and an output voltage detection circuit 22 is connected between the terminals 12 and 13.

The operation of such a circuit configuration will be described. When a DC input voltage Vi such as a pulsating current is applied between the input terminal 10 and the ground terminal 11, the capacitor 2
3 is smoothed, a current flows through the base of the switch element 18 through the resistor 28, and the switch element 18 is turned on. Then, an input voltage is applied to the primary winding 15 of the transformer 14 to accumulate energy, and a voltage is generated in the tertiary winding 17 having the same polarity. Due to the voltage generated in the tertiary winding 17, the resistor 29 and the capacitor 2
The base current of the switch element 18 flowing through the capacitor 5 flows, and at the same time, the charge is accumulated in the capacitor 27 via the diode 35.

When the collector current of the switch element 18 rises and reaches a certain value, the switch element 18 shifts to an off state, and at the same time, a counter electromotive force is generated in the secondary winding 16 of the transformer 14 and the output terminal 12, Power is released during 13.
Electric power is transmitted to the secondary side circuit by repeating such operations. When the output voltage exceeds the set value, the output voltage detection circuit 2
2 detects it, a current flows through the light emitting portion 20 of the photocoupler to emit light, and the light receiving portion 2 of the photocoupler of the primary side circuit
The light is received by 1 and a current flows, which causes the switch element 1
A base current flows through the switch element 9, and the switch element 19 is turned on. When the switch element 19 is turned on, the current flowing through the resistor 28 to the base of the switch element 18 flows through the collector and the emitter of the switch element 19, and the switch element 18 is short-circuited and turned off during this period. Stay in the state. Secondary winding 16 of transformer 14
When the counter electromotive force is released, a slight residual energy generates a counter electromotive force in the tertiary winding 17, which causes a base current to flow in the switch element 18 and the switch element 1 again.
8 is turned on. By repeating such operation, stabilized electric power is transmitted.

By using the switching power supply circuit as described above, a stable power supply can be secured, and it can be used for AC power supplies of different voltages. However, in recent years, in order to be able to operate instantaneously at any time, it is necessary to use energy-saving measures in switching power supply circuits installed in electronic devices that have a high possibility of being used with input voltage always applied. Therefore, it has been required to reduce the power consumption of the switching power supply circuit when the electronic device or the like is not used.

When not in use, that is, in standby, the load of the output voltage Vo of the switching power supply circuit is zero or very small. In such a case, energy supply to the secondary side via the transformer 14 is continued. If continuously performed by such a switching operation, the supply voltage becomes excessive and the output voltage Vo rises. Actually, the output voltage V
Information for preventing o from exceeding the set value is fed back to the primary side through the light emitting unit 20 and the light receiving unit 21 of the photocoupler that insulates and transmits the output voltage detection signal, and the output voltage detection circuit 22 The switch element 18 is kept in the OFF state until the output voltage Vo is detected to decrease, and the energy supply is stopped. However, in order to hold the switch element 18 in the off state, the switch element 19 needs to continue to be turned on. Therefore, the capacitor 27 is used as a voltage source via the light receiving section 21 of the photocoupler to switch the switch element 1.
It must continue to supply current to the base of 9. In the conventional circuit, in order to supply a current to the base of the switch element 19, the voltage of the capacitor 27 is held for a necessary time.

[0010]

The problems in the above conventional switching power supply circuit and the problems to be solved by the present invention will be described below. (1) First Problem and Solution Problem In the conventional circuit, in order to keep the main switch element 18 in the off state, the switch element 19 must continue to be turned on, and the capacitor 27 must be turned on for the time required for that. As a source, a current must be supplied to the base of the switch element 19 via the light receiving portion 21 of the photocoupler. Therefore, power consumption of about (voltage of the capacitor 27) × (current supplied to the base of the switch element 19 and the resistors 30 and 31 via the light receiving portion 21 of the photocoupler) occurs even during standby. When the pulsating current obtained by rectifying and smoothing the AC input voltage or the DC voltage source Vi corresponding to the pulsating current becomes high, the primary winding 15 and the tertiary winding 17 have the same phase relationship. There is a problem that the power consumption increases in proportion to the power consumption, and as a result, the power consumption also increases. Although a slight improvement can be achieved by replacing the bipolar transistor as the switch element 18 with a MOSFET, the power consumption during standby is still large. A first problem to be solved by the present invention is to provide a switching power supply circuit capable of minimizing the power consumed by itself during standby.

(2) Second Problem and Solution Problem The diode 34, which has been forward biased by the voltage generated in the primary winding 15, has the main switching element 18
When turns from off to on, it is suddenly reverse-biased and a recovery current flows instantaneously. This flows as it is as a collector current of the switch element 18, and this current causes a large switching loss and a large noise. This instantaneously flowing collector current becomes proportionally large if the pulsating current obtained by rectifying and smoothing the AC input voltage or the DC voltage source Vi corresponding thereto rises.
There was a problem. A second problem to be solved by the present invention is to reduce the recovery current, reduce switching loss, and suppress noise generation.

(3) Third Problem and Solution Problem When the main switch element 18 shifts from on to off, the base of this switch element 18 has a tertiary winding while the switch element 18 is on. The voltage of the capacitor 25 charged positively in the one connected to the resistor 29 by the voltage generated in 17 is applied so that the emitter becomes positive and the base becomes negative, and the switch element 18 is turned off. Since the voltage generated in the tertiary winding 17 on the side of the resistor 29 which becomes negative is also added to this, a large negative voltage is instantaneously applied. As a result, the collector current suddenly changes to zero, and this abrupt change in collector current causes large noise. Further, there is a problem that a large reverse voltage having the same value as that of the base of the main switch element 18 is applied between the collector and the emitter of the control switch element 19. A third problem to be solved by the present invention is to prevent a reverse voltage from being applied between the collector and the emitter of the control switch element 19 and to prevent the main switch element 18 from turning on. The base voltage is to be discharged under a certain condition to suppress the generation of noise.

[0013]

According to the present invention, a DC voltage is switched by a main switch element 37 connected to a primary winding 15 of a transformer 14 to transfer energy to a secondary winding 16 of the transformer 14. This secondary winding 16
The output voltage detection information from the feedback unit 39 coupled to the above is fed back to the switching control unit 38 coupled to the tertiary winding 17 of the transformer 14 so as to control ON / OFF of the main switch element 37. In the switching power supply of the self-excited oscillation type, the switching element 37
Is a MOSFET, and the drive signal line connecting the gate of the switch element 37 and one end of the tertiary winding 17 is connected to the power supply side of the switching controller 38 to drive the switch element 37. The switching power supply circuit is characterized in that energy is used as a control signal of the switching control unit 38.

With such a configuration, the off period of the switch element 37 can be maintained without using the capacitor 27 as a voltage source used in the conventional circuit, and the diode 35 and the capacitor 27 of the conventional circuit can be maintained. By saving the consumed power, it is possible to suppress the power consumption during standby.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) An embodiment according to the present invention for solving the first problem will be described with reference to FIG. The primary side circuit with the transformer 14 as a boundary is different from the conventional circuit shown in FIG. 5 in that the main switch element 37 is composed of a MOSFET, and the light receiving transistor 21 as the light receiving section of the photocoupler of the switching control section 38. Is directly connected to the resistor 28 for starting, the capacitor 25 for supplying power, and the gate of the main switch element 37, and the circuit of the diode 35 and the capacitor 27 which are the voltage source of the switch element 19 for control is omitted. It is that. Regarding the secondary side circuit with the transformer 14 as the boundary, there is no difference from the conventional circuit shown in FIG.

The operation of such a circuit configuration will be described. When a DC input voltage Vi such as a rectified pulsating current is applied between the input terminal 10 and the ground terminal 11, after being smoothed by the capacitor 23, a minute current flows through the resistor 28 to the gate of the switch element 37. The switch element 37 is turned on. Then, the transformer 1
An input voltage is applied to the secondary winding 15 to accumulate energy, and a voltage is generated in the tertiary winding 17 having the same polarity. This voltage causes resistance 29 from the side of the tertiary winding 17 as well.
A voltage is applied to the gate of the main switch element 37 via the capacitor 25 and the ON state continues. When the drain current of the switch element 37 reaches a certain value, the switch element 37 shifts to the off state, and at the same time, the counter electromotive force is generated in the secondary winding 16 of the transformer 14, and the output terminal 1
Electric power is discharged between 2 and 13. 2 of transformer 14 at the same time
A back electromotive force is generated in the next winding 16 and is stored in the capacitor 24 via the diode 33. When the back electromotive force of the secondary winding 16 is released, a small amount of residual energy is generated in the tertiary winding 1.
A counter electromotive force is generated in the switch element 3
The gate voltage of 7 is applied, and the switch element 37 is turned on again. Such operation is repeated to repeat the switching operation.

In this way, when the voltage between the output terminals 12 and 13 reaches a predetermined voltage, the output voltage detection circuit 22 detects it and a current flows through the light emitting section 20 of the photocoupler to emit light. The light receiving unit 21 of the photocoupler of the circuit receives the light and turns it on. Then, the resistance 29 from the side of the tertiary winding 17
The drive current of the main switch element 37 supplied via the capacitor 25 flows as a base current of the switch element 19 through the light receiving portion 21 of the photocoupler, and the switch element 19 is turned on. When the switch element 19 is turned on, the resistor 2 is added to the base of the switch element 37.
The current flowing through 8 also flows through the switch element 19, and the switch element 37 is maintained in the OFF state during this period. In this way, the switch element 37 is turned off,
The amount of energy supplied to the primary winding 15 of the transformer 14 is limited.

Here, the standby state is when the load of the output voltage Vo of the switching power supply circuit is zero or very small. In such a case, if the energy is continuously supplied to the secondary side through the transformer 14 by the continuous switching operation, the supply voltage becomes excessive and the output voltage Vo rises.
The output voltage Vo is detected by the output voltage detection circuit 22 so that the output voltage Vo does not exceed the set value, and the output voltage detection signal as information is insulated and transmitted.
The output voltage detection circuit 22 is fed back to the secondary circuit.
Until the switch detects the decrease of the output voltage Vo.
Must be kept off to stop the energy supply.

Therefore, in the circuit of the present invention, the switch element 3
In order to keep 7 turned off, capacitor 25 and resistor 2
The light emitting portion 21 of the photocoupler is connected to the connection side with 8, and the starting current for turning on the switch element 37 is absorbed by the light emitting portion 21 of the photocoupler and the switch element 19 is kept on. Therefore, the oscillation is surely stopped in the secondary side circuit until the output voltage Vo decreases. In the conventional circuit, the capacitor 27 used to stop the oscillation was the cause of increasing the power consumption, but in the present invention, the same oscillation can be stopped without using the capacitor 27, and further, the power consumption can be increased. It is possible to reduce the consumption. At the same time, the number of parts can be reduced, the circuit configuration can be simplified, and the cost can be provided at a low cost. Although the resistor 29 and the capacitor 25 are connected in this order between the tertiary winding 17 and the gate of the switch element 37 in FIG. 1, the capacitors 25 and 29 may be connected in that order.

(2) An embodiment according to the present invention for solving the second problem will be described with reference to FIG. The difference from the circuit shown in FIG. 5 is that a resistor 40 is inserted in the gate of the main switch element 37. That is, one end A of the resistor 40 is connected to the connection point of the resistor 28, the capacitor 25, the light receiving portion 21 of the photocoupler, and the collector of the switch element 19, and the other end B of the resistor 40 is connected to the switch element 37.
It is the point connected to the gate. A diode 41 is provided between the ground terminal 11 side of the tertiary winding 17 and the one end A.
There is also a difference in inserting the, but this will be described later.

The operation of such a configuration will be described. In the conventional circuit shown in FIG.
Is switched from off to on, the base of the switch element 18 has a transformer 1 while the switch element 18 is off.
Due to the voltage generated in the tertiary winding 17 of No. 4, the voltage of the capacitor 25, which is positively charged to the one connected to the resistor 28, is rapidly applied. As a result, the switch element 18 is rapidly turned on, so that the recovery current of the diode 34 of the snubber circuit 36 that absorbs the surge voltage generated in the primary winding 15 of the transformer 14 flows.

Therefore, in the present invention, as shown in FIG.
By connecting the resistor 40 between the point A and the point B on the drive signal line, a voltage gradually increasing is applied to the gate of the switch element 37. As a result, the switch element 37 turns on gently and the diode 3
Since the recovery current of 4 also becomes small, the switching element 37
The noise generated by the switching loss and the recovery current of the diode 34 can be reduced.

Although the collector of the switch element 19 is connected to the point A in the circuit example of FIG. 2, the connection may be changed from the point A to the point B as shown by the dotted line in FIG. By connecting in this manner, the gate voltage control gain of the switch element 37 can be adjusted in addition to the above-described effect.

(3) An embodiment according to the present invention for solving the third problem will be described with reference to FIG. In the conventional circuit shown in FIG. 5, when the switch element 18 shifts from on to off, the resistance of the base of the switch element 18 is increased by the voltage generated in the tertiary winding 17 while the switch element 18 is on. The voltage of the capacitor 25, which is positively charged on the side connected to 29, is suddenly applied so that the emitter becomes positive and the base becomes negative, and the switch element 18 is turned off to turn the tertiary winding 17 on. Since the generated voltage which becomes negative on the resistance 29 side is also added, a large negative voltage is instantaneously applied.

Therefore, as shown in FIG.
When 1 is connected so that its cathode becomes the point A where the resistor 28 and the capacitor 25 are connected and its anode becomes the emitter of the switch element 19, it is connected to the resistor 29 when the switch element 37 shifts from on to off. The voltage of the capacitor 25 charged positively is
9, discharged through the path of the tertiary winding 17 and the diode 41. Since the anode side of the diode 41 is connected to the ground terminal 11 side, the cathode side is clamped with a negative forward voltage, and thus a large instantaneous reverse voltage is applied between the collector and the emitter of the switch element 19. In addition, since the series connection circuit of the resistor 31, the source / gate of the switch element 37, and the resistor 40 is connected in parallel with the diode 41, the gate voltage of the switch element 37 passes through the resistors 31 and 40. It can be discharged under constant conditions. Here, by adjusting the value of the resistor 40, the change in the drain current of the switch element 37 can be adjusted to an arbitrary condition that reduces the generation of noise.

In the embodiment shown in FIG. 2, the one inserted between the ground terminal 11 side of the tertiary winding 17 and the one end A is a diode 41, but a Zener diode is provided in place of this diode 41. May be. By providing the Zener diode, when the pulsating current obtained by rectifying and smoothing the AC input voltage or the DC voltage source Vi corresponding thereto is high, the gate of the switch element 37, the collector of the switch element 19, and the collector of the light receiving transistor 21 of the photocoupler. The high voltage applied to can be clamped to any value.

(4) A more effective embodiment of the present invention for solving the second and third problems will be described with reference to FIG. In the embodiment shown in FIG. 2, the resistor 40 is connected between the points A and B to reduce the generation of noise. This effect becomes more remarkable as the value of the resistor 40 increases. On the other hand, however, the gate voltage when the switch element 37 shifts from on to off changes slowly, and the decrease in drain current also slows down.

Therefore, as shown in FIG.
Further, a series circuit of the diode 42 and the resistor 43 is connected in parallel so that the anode side of the diode 42 is the gate side of the MOSFET 37. Then, the voltage change when the switch element 37 shifts from on to off can be adjusted to an arbitrary state. That is, when the switching element 37 is turned on, the gate is charged only through the resistor 40, but when the gate is turned off, it is discharged through the series connection of the diode 42 and the resistor 43 in addition to the resistor 40. Therefore, the decreasing rate of the drain current at the time of turning off can be arbitrarily set by adjusting the values of the resistors 40 and 43. Also in this circuit, by changing the connection of the collector of the control switch element 19 from the point A to the point B, the gate voltage control gain of the switch element 37 can be adjusted in addition to the above effects.

(5) FIG. 4 shows an embodiment according to the present invention for solving the first, second and third problems with a minimum number of parts.
Is shown in. The circuit shown in FIG. 4 differs from the circuit shown in FIG. 2 in that a resistor 44 is provided between the base of the switch element 19 and one end of the tertiary winding 17.
That is, by combining the current detection resistor 31 of the main switch element 37 and the resistor 30 for transmitting the voltage detected by the resistor 31 to the control switch element 19 with the resistor 44, the AC input voltage is changed. When the rectified and smoothed pulsating current or the corresponding DC voltage source Vi changes, the maximum current value of the switch element 37 is corrected according to this change, and the first, second, and third problems are minimized. It can be solved with limited parts.

[0030]

According to the first aspect of the invention, in the self-oscillation type switching power supply, the switch element 37 is
A power supply side of a switching control unit 38 is connected to a drive signal line which is composed of a MOSFET and which connects the gate of the switching element 37 and one end of the tertiary winding 17, and the energy for driving the switching element 37 is controlled by the switching control. Since it is used as the control signal of the section 38, the off period of the main switch element 37 can be maintained without using the diode 35 and the capacitor 27 used in the conventional circuit, and compared with the conventional circuit. It is possible to significantly reduce the consumption of standby power. By the way, according to the experimental results comparing the circuit of the present invention and the conventional circuit, the standby power consumption is more than that of the case where the conventional bipolar transistor 18 is used and the case where the bipolar transistor is replaced with a MOSFET. ,
In the circuit of the present invention, it was possible to significantly reduce the amount to about 1/3 to 1/5.

According to the second aspect of the invention, the feedback section 39 comprises the output voltage detection circuit 22 and the light emitting section 20 of the photocoupler for outputting the output voltage detection information detected by the output voltage detection circuit 22. The switching control unit is turned on when receiving the output voltage detection information and the light receiving unit 21 of the photocoupler that receives the output voltage detection information.
The control switch element 19 is formed of a bipolar transistor that turns off the FET 37. The photocoupler's light receiving portion 21 and the collector of the control transistor 19 and the MOSFET 37 are connected from one end of the tertiary winding 17 via a resistor 29 and a capacitor 25. While connected to the gate and the photodetector 20 of the photocoupler is on, the control transistor 19
Is kept on by the energy from the tertiary winding 17 and MO
Since the off period of the SFET 37 is made to continue, the light receiving portion 21 of the photocoupler and the control transistor 1 are
The output voltage on the secondary side can be controlled by 9, and the transistor 19 supplies the gate drive current supplied to the MOSFET 37, which is the main switch element,
Since the base current is directly absorbed by the control transistor 19, power consumption can be suppressed.

According to the invention of claim 3, the MOSFE
In the gate drive signal line of T37, the reverse voltage clamp and the rectifying diode 41 are connected so that the power supply side of the switching control unit 38 is the cathode and the ground side is the anode. It is possible to prevent a momentary and large reverse voltage from being applied between the two, and the series connection circuit of the resistor 31, the source / gate of the switch element 37 and the resistor 40 is connected in parallel with the diode 41. The gate voltage of 37 can be discharged under constant conditions through the resistors 31 and 40. Further, by adjusting the value of the resistor 40, the change in the drain current of the switch element 37 can be adjusted to an arbitrary condition that reduces the generation of noise.

According to the invention of claim 4, the MOSFE
In the gate drive signal line of T37, the reverse voltage clamp and the rectifying Zener diode 41 are connected so that the power supply side of the switching control unit 38 is the cathode and the ground side is the anode. Therefore, the AC input voltage is rectified and smoothed. When the pulsating current or the corresponding DC voltage source Vi is high, the gate of the switch element 37, the collector of the switch element 19, and the light receiving transistor 21 of the photocoupler.
The high voltage applied to the collector of can be clamped to any value.

According to the invention of claim 5, the transformer 1
In parallel with the primary winding 15 of 4, the diode 34, the resistor 3
2, the snubber circuit 36 including the capacitor 26 is provided,
The drive signal line between the gate of the MOSFET 37 and the cathode of the diode 41 is provided with the resistor 40 for reducing the gate voltage change of the MOSFET 37 in order to reduce the recovery current of the diode 34.
The increase in the voltage applied to the gate of the FET 37 becomes gentle, and the switch element 37 is gently turned on.
As a result, noise generated by the switching loss of the switch element 37 and the recovery current flowing through the diode 34 can be reduced. This effect has a sufficient margin with respect to the VCCI standard.

According to the sixth aspect of the invention, a series circuit of a diode 42 and a resistor 43 is provided in parallel with the resistor 40 for suppressing the recovery current of the diode 34, and the anode side of the diode 42 is the gate side of the MOSFET 37. Since the connection is made in this manner, it is possible to adjust the voltage change when the switch element 37 shifts from on to off to an arbitrary state. That is, when the switching element 37 is turned on, the gate is charged only through the resistor 40, but when the gate is turned off, it is discharged through the series connection of the diode 42 and the resistor 43 in addition to the resistor 40. Therefore, the decreasing rate of the drain current at the time of turning off can be arbitrarily set by adjusting the values of the resistors 40 and 43.

According to the seventh aspect of the invention, the power supply side of the switching control section 38 is connected between the resistor 40 for suppressing the recovery current of the diode 34 and the gate of the MOSFET 37. Or 6
The gate voltage control gain of the switch element 37 can be adjusted with the effect described.

According to the eighth aspect of the invention, the current detecting resistor 31 of the main switch element 37 and the resistor 31 are provided.
When the pulsating current obtained by rectifying and smoothing the AC input voltage or the DC voltage source Vi corresponding to the rectifying and smoothing the AC input voltage is changed, the resistance 30 for transmitting the voltage detected by the control switch element 19 to the resistor 30 is further combined. In addition, the maximum current value of the switch element 37 is corrected according to this change,
The second and third problems can be solved with a minimum number of parts.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of a switching power supply circuit according to the present invention.

FIG. 2 is an electric circuit diagram showing a second embodiment of the switching power supply circuit according to the present invention.

FIG. 3 is an electric circuit diagram of a main part showing a third embodiment of the switching power supply circuit according to the present invention.

FIG. 4 is an electric circuit diagram showing a fourth embodiment of the switching power supply circuit according to the present invention.

FIG. 5 is an electric circuit diagram showing a conventional switching power supply circuit.

[Explanation of symbols]

Vi ... pulsating current obtained by rectifying and smoothing AC input voltage or DC voltage corresponding thereto, Vo ... Output voltage, 10 ... Input terminal, 11
... ground terminal, 12 ... output terminal, 13 ... ground terminal, 14 ... transformer, 15 ... transformer primary winding, 16
... secondary winding of transformer, 17 ... tertiary winding of transformer, 1
8 ... Main switch element, 19 ... Control switch element, 20 ... Photocoupler light emitting section, 21 ... Photocoupler light receiving section, 22 ... Output voltage detection circuit, 23-27 ... Capacitors, 28-32, 40, 43, 44 ... Resistance, 33-
35, 41, 42 ... Diode, 36 ... Snubber circuit, 3
7 ... Main switch element, 38 ... Switching control unit, 39 ... Feedback unit.

Claims (8)

[Claims] 1. A primary winding 15 of a transformer 14 for applying a DC voltage.
Is switched by the main switching element 37 connected to the secondary winding 16 of the transformer 14 to transfer energy, and the output voltage detection information from the feedback unit 39 coupled to the secondary winding 16 is transferred to the secondary winding 16 of the transformer 14. Transformer 14
In the self-excited oscillation type switching power source which is fed back to the switching control unit 38 coupled to the tertiary winding 17 and controls the on / off of the main switch element 37, the switch element 37 is a MOSFET. And the gate of the switch element 37 and the tertiary winding 17
The power supply side of the switching control unit 38 is connected to a drive signal line that is connected to one end of the switching control unit 38, and the energy for driving the switch element 37 is used as a control signal of the switching control unit 38. Switching power supply circuit. 2. The feedback section 39 comprises an output voltage detection circuit 22 and a photocoupler light emitting section 20 for outputting output voltage detection information detected by the output voltage detection circuit 22, and the switching control section outputs the output voltage. The photo-coupler light-receiving portion 21 receives the voltage detection information, and the control switch element 19 is formed of a bipolar transistor that is turned on when the output voltage detection information is received to turn off the MOSFET 37. Resistance 2 from one end
9 through the condenser 25 and the light receiving portion 21 of the photocoupler.
And collector of control transistor 19 and MOSFET 3
While the light receiving portion 20 of the photocoupler is turned on by being connected to the gate of the MOSFET 7, the control transistor 19 is kept on by the energy from the tertiary winding 17 and the MOSFET 3 is turned on.
7. The switching power supply circuit according to claim 1, wherein the OFF period of No. 7 is continued. 3. A gate drive signal line of the MOSFET 37, wherein a reverse voltage clamp and a rectifying diode 41 are connected so that the power supply side of the switching control section 38 is a cathode and the ground side is an anode. The switching power supply circuit according to claim 1 or 2. 4. The gate drive signal line of the MOSFET 37, wherein the reverse voltage clamp and the rectifying Zener diode 41 are connected so that the power supply side of the switching control unit 38 is the cathode and the ground side is the anode. The switching power supply circuit according to claim 1 or 2. 5. The primary winding 15 of the transformer 14 in parallel,
A snubber circuit 36 including a diode 34, a resistor 32, and a capacitor 26 is provided, and a gate voltage of the MOSFET 37 is suppressed in the drive signal line between the gate of the MOSFET 37 and the cathode of the diode 41 in order to suppress the recovery current of the diode 34 to be small. 5. A resistor 40 for reducing the change is provided, and the resistor 40 is provided.
The switching power supply circuit described. 6. A series circuit of a diode 42 and a resistor 43 is provided in parallel with a resistor 40 for suppressing a recovery current, and an anode side of the diode 42 has a MOSFET 3 therein.
7. The switching power supply circuit according to claim 5, wherein the switching power supply circuit is connected so as to be on the gate side of 7. 7. The switching power supply circuit according to claim 5, wherein the power supply side of the switching control section 38 is connected between the resistor 40 for suppressing the recovery current and the gate of the MOSFET 37. 8. A DC voltage obtained by rectifying and smoothing an AC input voltage is switched by a main switch element 37 connected to a primary winding 15 of a transformer 14, and the transformer 1
4 transmits the energy to the secondary winding 16 and outputs the output voltage detection information from the feedback section 39 coupled to the secondary winding 16 to the switching control section coupled to the tertiary winding 17 of the transformer 14. In the self-excited oscillation type switching power supply which is controlled by turning on / off the main switch element 37 by returning to 38, the switch element 37 is composed of a MOSFET.
Is connected to the input terminal 10 via the primary winding 15 and the source is connected to the ground terminal 11 via the resistor 31. The feedback section 39 detects the output voltage detecting circuit 22 and the output voltage detecting circuit 22. The switching control section 38 includes a light emitting diode 20 as a light emitting section of a photocoupler for outputting the output voltage detection information detected by the circuit 22, and the switching control section 38 serves as a light receiving transistor as a light receiving section of the photocoupler for receiving the output voltage detection information. 21 and a control switch element 19 composed of a bipolar transistor which is turned on when the output voltage detection information is received and turns off the MOSFET 37. The collector and the emitter of the light receiving transistor 21 are the collectors of the control transistor 19, respectively. And the base, and the base of the control transistor 19 Via said resistor 30 MOSFET
37 connected to the source of
This control transistor 1 is connected to one end of the next winding 17.
The emitter of 9 is connected to the ground terminal 11, a snubber circuit 36 including a diode 34, a resistor 32, and a capacitor 26 is provided in parallel with the primary winding 15 of the transformer 14, and the gate of the MOSFET 37 and the cathode of the diode 41 are provided. In order to suppress the recovery current of the diode 34 in the drive signal line between
A resistor 40 that alleviates a change in the gate voltage of the SFET 37 is provided, and the gate drive signal line of the MOSFET 37 is connected to the collector of the light receiving transistor 21 and the collector of the control transistor 19 which are the power supply side in the switching control unit 38. A switching power supply circuit characterized in that a reverse voltage clamp and a rectifying diode 41 are connected so that a connection point side is a cathode and a ground side is an anode.