JPH11341806A - Switching power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source circuit a DC voltage compensating circuit which has incorporated therein, which supplies a DC voltage within the level for compensating the action of the circuit element of an IC, etc., mounted in the switching power source circuit with respect to the potential fluctuation of an input AC voltage supplied from an AC power source to the circuit element. SOLUTION: In a switching power source circuit 1 which rectifies an input AC voltage by means of a rectifier circuit D3 and supplies a prescribed voltage to a secondary-side circuit by impressing a pulse voltage upon a transformer T1, in accordance with an oscillation signal outputted from an IC 20 based on the rectified DC voltage from the circuit D3, the potential at the base electrode of a transistor Tr1 is fixed, when the value of the DC voltage outputted from the circuit D3 is larger than a prescribed value, because a reverse voltage having a reverse breakdown voltage value flows at a fixed level into a Zener diode ZD1. The DC voltage supplied to the IC 20 is compensated by interrupting the flow of the base current of the transistor TR1 and supplying electric power to the IC 20 from the auxiliary coil T3 of the transformer T1.

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 for supplying power to an electronic circuit using an IC or the like.

[0002]

2. Description of the Related Art Conventionally, a switching power supply circuit has been used as a power supply circuit for supplying stable electric power to an electronic circuit using an IC (Integrated Circuit) or the like. Here, an example of a conventionally used switching power supply circuit is shown in FIG.

FIG. 3 shows a conventional switching power supply circuit 10.
FIG. 3 is a circuit diagram illustrating a configuration of a zero. The switching power supply circuit shown in FIG. 3 supplies power to the secondary circuit by connecting an AC power supply to the input terminal 41 and the input terminal 42.

The switching power supply circuit 10 shown in FIG.
0, the AC voltage input to the input terminals 41 and 42 is full-wave rectified by the rectifier circuit D3, and the rectifier circuit D3
Outputs a DC voltage corresponding to the AC voltage level input to the input terminals 41 and 42. The DC voltage output from the rectifier circuit D3 is input to the power supply terminal 22 of the IC 20 via the resistor R2 and to the transformer T1.

Here, the IC 20 starts an oscillating operation when a DC voltage is input to the power supply terminal 22.
The output terminal 21 of the IC 20 is connected to an FET (Field-Effect Tra
nsistor: field effect transistor) 50 gate terminal G
The high-frequency pulse generated by the oscillation operation of the IC 20 is output from the output terminal 21 to the gate terminal G1 of the FET 50. In the FET 50, while a high-frequency pulse is being input from the IC 20 to the gate terminal G1, conduction is established between the drain terminal and the source terminal, so that a high-frequency pulse voltage is applied to the transformer T1. As a result, a voltage is supplied from the transformer T1 to the secondary circuit.

The transformer T1 has an auxiliary coil T3 for supplying a voltage to the power supply terminal 22 of the IC 20, in addition to a main coil T2 for supplying a voltage to the secondary circuit. The voltage supplied from the transformer T1 to the auxiliary coil T3 is rectified by the diode D2 and the capacitor C1 and supplied to the power supply terminal 22 of the IC 20.

[0007]

In the conventional switching power supply circuit 100, the pulse voltage generated by the auxiliary coil T3 of the transformer T1 is rectified by the diode D2 and the capacitor C1 and is rectified by the power supply terminal 2 of the IC 20.
2, the potential of the DC voltage supplied to the IC 20 depends on the potential of the AC voltage input to the input terminals 41 and 42.

Further, since the power supply voltage range is set as a rating for compensating the operation of the IC 20, the DC voltage range supplied to the power supply terminal 22 via the diode D2 and the capacitor C2 corresponds to the input terminal. Since it is affected by the fluctuations in the potential of the AC voltage input to 41 and 42, it is necessary to limit the fluctuations in the potential of the input AC voltage to a voltage range that compensates for the operation of the IC 20.

For this reason, the AC power supply connected to the input stage of the switching power supply circuit 100 is used in a state where the range of the potential fluctuation is narrow, and the use range of the power supply device or the device on which the switching power supply circuit is mounted is limited. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems by applying an operation to a circuit element such as an IC mounted in a switching power supply circuit in response to a potential change of an input AC voltage supplied from an AC power supply. An object of the present invention is to provide a switching power supply circuit incorporating a DC voltage compensating circuit for supplying a DC voltage in a range to be compensated.

[0011]

According to a first aspect of the present invention, there is provided a rectifier circuit (D3) for rectifying an input power supply voltage and outputting a predetermined DC voltage. A primary side coil is connected in series on the potential side output line, and a switching operation of a field effect transistor (50) connected downstream of the primary side coil causes a DC voltage output from the rectifier circuit to a predetermined oscillation. A transformer (T1) for transforming the voltage into an AC voltage having a frequency and transmitting the AC voltage to the secondary coil (T2) and the auxiliary coil (T3); and a drain electrode connected in series with the primary coil of the transformer (T1). A source electrode is connected in series on a low potential side output line of the circuit (D3), and a signal output terminal (21) of a switching control IC (20) and a gate electrode (G
1) is connected, a field effect transistor (50) that performs a switching operation by a switching signal input from a switching control IC (20), and an anode electrode at one end of the auxiliary coil (T3) of the transformer (T1). Is connected to the cathode electrode of the first diode (D2) connected to the power supply terminal (22), the gate electrode (G1) of the field effect transistor (50) and the signal output terminal (2).
1) is connected, and a ground terminal (2
3) is connected to the field effect transistor (50) using a DC voltage supplied from the rectifier circuit (D3) and the auxiliary coil (T3) of the transformer (T1) as a voltage source.
A switching IC (20) for outputting a switching signal for controlling the switching operation timing to the gate electrode (G1) of the field effect transistor (50), and an anode at one end of an auxiliary coil (T3) of the transformer (T1). Electrodes are connected and the switching IC (2
0) a first diode (D2) having a cathode electrode connected to a line connected to a power supply terminal (22), and one end connected to the cathode electrode of the first diode;
The other end of the auxiliary coil (T3) and a switching IC
In a switching power supply circuit comprising a capacitor (C1) having the other end connected to the ground terminal (23) of (20), a high potential side output line of the rectifier circuit (D3) is connected to a collector electrode. A base electrode is connected to the high potential side output line via a resistor, and a second electrode is connected to the emitter electrode side.
The transistor (TR1) to which the anode electrode of the diode (D1) is connected, the emitter electrode and the anode electrode of the transistor (TR1) are connected, and the power supply terminal (22) of the switching control IC (20) and the cathode electrode A Zener diode in which a base electrode and a cathode electrode of the transistor (TR1) are connected, and an anode electrode is connected to a low potential side output line of the rectifier circuit (D3). (ZD
1) and a Zener diode (ZD) connected between the base electrode of the transistor (TR1) and the low potential side output line.
When the potential of the base electrode of the transistor (TR1) becomes constant by the Zener voltage value set in 1), the power supply terminal of the switching control IC (20) is connected from the auxiliary coil (T3) of the transformer (T1). (22)
The DC voltage supplied to the power supply is compensated.

Therefore, in a switching power supply circuit including an IC or the like, the collector-emitter of the transistor is used until the potential fluctuation of the input AC voltage reaches the Zener voltage value from the lower limit of the voltage range for compensating the operation of the IC or the like. Supply to IC etc. by the collector current flowing between the electrodes,
When the input AC voltage exceeds the Zener voltage, power is supplied by the auxiliary coil,
A DC voltage within a range that compensates for the operation can be supplied. As a result, it is not necessary to use the AC power supply connected to the input stage of the switching power supply circuit in a state where the range of potential fluctuation is particularly narrow, and the range of use of a power supply device or device equipped with the switching power supply circuit is limited. Can be used without.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a circuit diagram showing a configuration of a switching power supply circuit 1 according to an embodiment of the present invention. As shown in FIG. 1, the switching power supply circuit 1 includes input terminals 11 and 12 connected to an AC power supply (not shown), a rectifier circuit D
3, a resistor R1, a Zener diode ZD1, a transistor TR1, an FET 50, diodes D1 and D2, a transformer T1, a capacitor C1, and an IC 20. FIG. 2 shows a portion of the switching power supply circuit 1 shown in FIG. 1 which constitutes the IC power supply circuit 10 for supplying power to the IC 20.
The IC power supply circuit 10 shown in FIG. 2 includes a resistor R1, a transistor TR1, a Zener diode ZD1, diodes D1 and D2, a capacitor C1, and an auxiliary coil T3 provided in a transformer T1. In addition,
Parts having the same configuration as the conventional switching power supply circuit 100 shown in FIG. 3 are denoted by the same reference numerals.

As shown in FIG. 1, the switching power supply circuit 1 has input terminals 11 and 12 connected to an AC power supply, and the input terminals 11 and 12 are connected to a rectifier circuit D3. The rectifier circuit D3 is a circuit for converting an AC voltage input through the input terminals 11 and 12 into a DC voltage and outputting the DC voltage, and is configured by, for example, a diode bridge circuit. When an AC voltage is input to the input terminals 11 and 12, a full-wave rectified DC voltage is output from the output terminals 13 and 14 of the rectifier circuit D3.

One end of a resistor R1 is connected to a line connected to the output terminal 13 of the rectifier circuit D3 at a node N1, and a collector electrode of the transistor TR1 and a transformer T1 are connected to a node N7 on the same line. Is connected to one end. The transformer T1 has a secondary circuit 30
A main coil T2 for supplying electric power to the power supply and an auxiliary coil T3 to be described later.

The node N2 on the line to which the other end of the resistor R1 is connected is connected to the base electrode of the transistor TR1 and the cathode terminal of the Zener diode ZD1. Zener diode ZD1
When the reverse voltage applied to the cathode side terminal is smaller than the reverse withstand voltage value of the Zener diode ZD1, the reverse current is cut off in the same manner as a normal diode,
When the reverse voltage exceeds the reverse withstand voltage value, the reverse current having the reverse withstand voltage value is passed, and the potential at the node N2 is set to the reverse withstand voltage value.

A rectifier circuit D is connected to a node N3 on the line to which the anode terminal of the Zener diode ZD1 is connected.
3 is connected to the output terminal 14, and the source terminal of the FET 50 is connected to the line connected to the output terminal 14 of the rectifier circuit D3. The node N8 on this line is connected to a node N5 on a line connected to a ground terminal 23 of the IC 20 described later.

On the other hand, the other end of the transformer T1 is connected to the drain terminal of the FET 50, and the DC voltage output from the output terminal 13 of the rectifier circuit D3 is applied to the transformer T1.
Is input through the main coil T2. The output terminal 21 of the IC 20 is connected to the gate terminal of the FET 50. As described later, the pulse voltage output from the output terminal 21 by the oscillation operation of the IC 20 is input to the gate terminal of the FET 50, thereby The connection between the source terminal and the drain terminal is made conductive, and the line connected between the other end of the main coil T2 of the transformer T1 and the output terminal 14 of the rectifier circuit D3 becomes conductive.

Transistor TR1 having a collector electrode connected to node N7 and a base electrode connected to node N2.
The anode terminal of the diode D1 is connected to the emitter electrode, and the node N4 on the line connected to the power supply terminal 22 of the IC 20 is connected to the cathode terminal of the diode D1. Further, one end of the capacitor C1 is connected to the node N4. A node N6 on a line connected to the other end of the capacitor C1 has a line to which the ground terminal 23 of the IC 20 is connected,
The ground point is connected.

One end of an auxiliary coil T3 of the transformer T1 is connected to a line connected to the ground terminal 23 of the IC 20, and a diode D2 is connected to the other end of the auxiliary coil T3.
Of the diode D2 is connected to a node N4 on a line connected to the power supply terminal 22 of the IC 20.

Here, the number of windings in the auxiliary coil T3 of the transformer T1 is set so as not to exceed the power supply voltage range of the IC 20. That is, the auxiliary coil T3 is I
To supply power to C20, the auxiliary coil T3
It is necessary that the voltage value output to the IC 20 does not exceed the power supply voltage range of the IC 20. For this reason, the number of windings in the auxiliary coil T3 of the transformer T1 is set such that a voltage value corresponding to the upper limit of the power supply voltage range of the IC 20 is output when the voltage value applied to the transformer T1 is the maximum value. .

The operation of the IC power supply circuit 10 (FIG. 2) in the switching power supply circuit 1 configured as described above will be described below.

First, when an AC voltage is input to the rectifier circuit D3 (FIG. 1), a DC voltage is output from the output terminal 13 of the rectifier circuit D3.
At 1, the voltage is applied to the collector electrode of the transistor TR1 and is input to one end of the resistor R1. Then, the DC voltage output from the other end of the resistor R1 is applied to the base electrode of the transistor TR1 at the node N2. Here, in the transistor TR1, when a DC voltage is applied to both the collector electrode and the base electrode, a DC current is output from the emitter terminal.
Is input to the anode electrode. Therefore, the diode D
DC voltage is output from the cathode electrode of
At 4, the voltage is applied to the power supply terminal 22 of the IC 20.

When a DC voltage is applied to the power supply terminal 22 of the IC 20, the IC 20 starts an oscillating operation, and a pulse voltage is output from the auxiliary coil T3 of the transformer T1 (FIG. 1) as described later.

Here, the DC voltage output from the auxiliary coil T3 is a power supply voltage value for compensating the operation of the IC 20 when the DC voltage output from the output terminal 13 of the rectifier circuit D3 (FIG. 1) is the maximum. Is set to be the upper limit. Therefore, when the DC voltage value output from the output terminal 13 of the rectifier circuit D3 is lower than the maximum value, the DC voltage output from the auxiliary coil T3 is lower than the lower limit of the rated range for compensating the operation of the IC 20. Smaller than that, and the IC 20 cannot be operated. For this reason, the IC 20 detects the diode D1 by the emitter current of the transistor TR1.
Is driven by the DC voltage output from the cathode electrode of the.

Here, when the AC voltage value input to the rectifier circuit D3 rises for some reason and the DC voltage value output from the output terminal 13 increases, the voltage value applied to the resistor R1 at the node N1 increases. By doing
The DC voltage value output to node N2 via resistor R1 increases.

Here, when the potential difference between the potential at the node N2 and the potential at the node N3 on the line connected to the output terminal 14 exceeds the reverse breakdown voltage (zener voltage) of the Zener diode ZD1. , A reverse current flows from the cathode electrode of the Zener diode ZD1 to the anode electrode. Since the voltage value of this reverse current is kept constant at the reverse breakdown voltage value of Zener diode ZD1, the potential of node N2, that is, the potential of the base electrode of transistor TR1, is kept constant.

On the other hand, as the DC voltage value output from output terminal 13 increases, the voltage value of the pulse voltage output from auxiliary coil T3 of transformer T1 (FIG. 1) increases. The pulse voltage output from the auxiliary coil T3 is rectified by the diode D2 and the capacitor C1, and is output to the node N4 on the line connected to the power supply terminal 22 of the IC 20.

At this time, the voltage value of the voltage output from the auxiliary coil T3, that is, the potential difference between the node N4 and the node N6 on the line connected to the ground terminal is the reverse withstand voltage of the Zener diode ZD1. When the value is larger than the value, the base current stops flowing in the transistor TR1, so that the transistor TR1 is turned off, and the power supply from the transistor TR1 to the power terminal 22 of the IC 20 is stopped. Then, power is supplied to the IC 20 from the auxiliary coil T3 with respect to the power supply terminal 22.

As described above, power is supplied to the power terminal 22 of the IC 20 from the emitter terminal of the transistor when the DC voltage output from the output terminals 13 and 14 of the rectifier circuit D3 is low. When the DC voltage output from the main terminals 13 and 14 of the rectifier circuit D3 exceeds a predetermined voltage value, power is supplied from the auxiliary coil T3. For this reason, even if the DC voltage output from the rectifier circuit D3 greatly fluctuates, power is supplied to the IC 20 within a rated range for compensating the operation of the IC 20.

By the above operation, the switching power supply circuit 1 shown in FIG. 1 performs the following operation.

When an AC voltage is input to the input terminals 11 and 12, the output terminal 13 of the rectifier circuit D3 inputs the input terminal 1
A DC voltage having a voltage value corresponding to the AC voltage input to each of the power supply units 1 and 12 is output. This output DC voltage is connected to the resistor R1
, And is input to the transistor TR1 as a collector voltage and further input to one end of the transformer T1.

Here, a resistor R is connected to the transistor TR1.
Since the DC voltage output from the other end of the transistor 1 is input as a base voltage, the collector-emitter of the transistor TR1 is turned on, and the DC voltage output via the diode D1 is input to the power terminal 22 of the IC 20. Is done.

The IC 20 performs an oscillating operation at a predetermined frequency when a DC voltage is input to the power supply terminal 22, and applies a pulse of the predetermined frequency to the gate terminal of the FET 50 connected to the output terminal 21. A voltage is output.

While the pulse voltage output from the output terminal 21 of the IC 20 is being input to the gate terminal of the FET 50, conduction between the source and the drain of the FET 50 is conducted, and the other end of the main coil T2 of the transformer T1 and the rectifier. The line connected between the circuit D3 and the output terminal 14 is in a conductive state. Therefore, when a pulse voltage is input from the output terminal 21 of the IC 20 to the gate terminal of the FET 50, a pulse voltage based on the DC voltage output from the rectifier circuit D3 is input to the transformer T1, so that the transformers T1 to 2
Power is supplied to the secondary circuit 30.

Further, from the main coil T2 of the transformer T1,
Power is also supplied to the auxiliary coil T3. And
The pulse voltage output from the auxiliary coil T3 is rectified by the diode D2 and the capacitor C1, and
Is output to the node N4 on the line connected to the power supply terminal 22.

Here, the number of windings of the auxiliary coil T3 is determined by the voltage output from the auxiliary coil T3 when the AC voltage input to the rectifier circuit D3 reaches the maximum voltage value in the fluctuation range. Is set to be lower than the upper limit of the rated range for compensating for the operation of. That is, even if the AC voltage value input to the rectifier circuit D3 is the maximum, the voltage output from the auxiliary coil T3 is set so as not to exceed the rated range of the IC 20. For example, if the rated range for compensating the operation of IC 20 is 11 V (volts) to 24 V, the number of turns of auxiliary coil T3 is set so that the voltage output from auxiliary coil T3 does not exceed 24 V. I have.

As described above, since the auxiliary coil T3 is set according to the time when the AC voltage input to the switching power supply circuit 1 reaches the maximum value, the AC voltage input to the switching power supply circuit 1 becomes the maximum value. If the value is smaller than the value, the voltage output from the auxiliary coil T3 to the node N4 may fall below the lower limit of the rated range of the IC 20. In this case, power cannot be supplied to the IC 20 by the auxiliary coil T3.
It is driven by the power supplied from R1.

Here, the peak voltage value of the AC voltage input to the input terminals 11 and 12 fluctuates greatly, and the rectifier circuit D3
When the voltage value of the DC voltage output from the output terminal 13 of the resistor R1 rises and exceeds a predetermined voltage value, the DC voltage input to the Zener diode ZD1 from the other end of the resistor R1 is opposite to that of the Zener diode ZD1. Exceeds the direction withstand voltage value. Then, in the Zener diode ZD1, a reverse current having a reverse withstand voltage value flows, and the potential difference between the cathode side terminal and the anode side terminal of the Zener diode ZD1 becomes constant at the reverse withstand voltage value of the Zener diode ZD1. Will be kept.

On the other hand, as the DC voltage value output from the rectifier circuit D3 increases, the voltage value of the pulse voltage output from the auxiliary coil T3 of the transformer T1 also increases. Since the pulse voltage is rectified and output to the node N4 as described above, the rise in the voltage value output from the rectifier circuit D3 causes the node N4 and the node N6 on the line connected to the ground terminal to be connected. The potential difference between the two increases.

The potential difference between the node N4 and the node N6 is the reverse breakdown voltage of the Zener diode ZD1, that is, the node N2 and the output terminal 1 of the rectifier circuit D3.
When the potential difference between the potential of the node and the potential of the line connected to the node N4 is exceeded, the potential of the node N4 becomes higher than the potential of the node N2, and the base current stops flowing in the transistor TR1. Therefore, the transistor TR1 is turned off, and the power supply from the transistor TR1 to the IC 20 is stopped.

However, since the voltage output from the auxiliary coil T3 of the transformer T1 is such that a voltage capable of supplying power to the IC 20 is input to the node N4, the power supply terminal 22 of the IC 20 is connected to the power supply terminal 22 of the IC 20. , Auxiliary coil T3
, And the IC 20 keeps operating stably.

Therefore, if the value of the AC voltage input to the input terminals 11 and 12 is an appropriate value, the IC 20
, Power is supplied by the transistor TR1, and when the voltage value of the AC voltage input to the input terminals 11 and 12 becomes a very large value, the IC 20 is assisted by the transformer T1. From coil T3, IC20
Is supplied within a power supply voltage range for compensating the operation of the power supply.
Thus, even when an AC voltage having a large peak voltage fluctuation is input to the input terminals 11 and 12,
A power supply voltage within a rated range for compensating the operation of the IC 20 is supplied to the IC 20, and the normal operation of the IC 20 can be maintained.

As described above, according to the switching power supply circuit 1 of the embodiment of the present invention, even when a DC voltage having a higher value than normal is input from the output terminal 13 of the rectifier circuit D3, the Zener diode ZD1 The reverse current of the reverse breakdown voltage value flows through the transistor T
The potential difference between the base and the emitter of R1 is maintained at a constant value, and the AC voltage supplied from the main coil T2 of the transformer T1 to the auxiliary coil T3 is rectified by the diode D2 and the capacitor C1 to generate a DC voltage value. As a result, the transistor TR1 is turned off, and power is supplied to the power terminal 22 of the IC 20 by the voltage output from the transformer T3. by this,
Even when an AC voltage having a large peak voltage fluctuation is input to the input terminals 11 and 12, the IC 20 can be supplied with a DC voltage within a rated range for compensating the operation and operate stably. . As a result, in the switching power supply circuit 1, fluctuations in the peak voltage of the AC power supply connected to the input stage can be tolerated to some extent, and the criteria for selecting the AC power supply can be set broadly, so that the power supply cost can be reduced. Becomes

[0046]

According to the first aspect of the present invention, I
In a switching power supply circuit including C and the like, until the potential fluctuation of the input AC voltage reaches the Zener voltage value from the lower limit of the voltage range for compensating the operation of the IC or the like, the collector current flowing between the collector and emitter electrodes of the transistor causes When the AC voltage supplied to an IC or the like exceeds the Zener voltage, a DC voltage within a range for compensating the operation can be supplied by supplying power using an auxiliary coil. As a result, it is not necessary to use the AC power supply connected to the input stage of the switching power supply circuit in a state where the range of potential fluctuation is particularly narrow, and the range of use of a power supply device or device equipped with the switching power supply circuit is limited. Can be used without.

[Brief description of the drawings]

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

2 is included in the switching power supply circuit shown in FIG.
It is a circuit diagram which extracts and shows an IC power supply circuit.

FIG. 3 is a circuit diagram showing a configuration of a conventional switching power supply circuit.

[Explanation of symbols]

Reference Signs List 1 switching power supply circuit 10 IC power supply circuit 11, 12 input terminal 20 IC 21 output terminal 22 power supply terminal 23 ground terminal 30 secondary circuit 50 FET C1 capacitor D1, D2 diode D3 rectifier circuit 13, 14, output terminal N1, N2, N3 , N4, N5, N6, N7, N8 nodes R1 resistor T1 transformer T2 main coil T3 auxiliary coil TR1 transistor ZD1 Zener diode

Claims (1)

[Claims] 1. A rectifier circuit for rectifying an input power supply voltage and outputting a predetermined DC voltage, a primary coil connected in series on a high-potential output line of the rectifier circuit, and a downstream side of the primary coil. A transformer for transforming a DC voltage output from the rectifier circuit into an AC voltage having a predetermined oscillation frequency and transmitting the AC voltage to a secondary coil and an auxiliary coil by a switching operation of a field-effect transistor connected to the transformer; A drain electrode is connected in series with the side coil, a source electrode is connected in series on the low potential side output line of the rectifier circuit, and a signal output terminal of the switching control IC and a gate electrode are connected, so that the switching control IC A field effect transistor that performs a switching operation in response to a switching signal input from the A cathode electrode of the first diode to which the ground electrode is connected, a power supply terminal, a gate electrode of the field effect transistor, a signal output terminal, and a ground terminal on a grounded line; A switching IC that outputs a switching signal for controlling a switching operation timing of the field-effect transistor to a gate electrode of the field-effect transistor using a rectifier circuit and a DC voltage supplied from an auxiliary coil of the transformer as a voltage source; A first diode having an anode electrode connected to one end of the auxiliary coil and a cathode electrode connected to a line connected to a power supply terminal of the switching IC; and one end connected to the cathode electrode of the first diode. And the other end of the auxiliary coil and the switching IC
And a capacitor having the other end connected to a ground terminal of the rectifier circuit, wherein a high-potential output line and a collector electrode of the rectifier circuit are connected to each other, and A transistor having a base electrode connected thereto, and an anode electrode of a second diode connected to the emitter electrode side; an emitter electrode and an anode electrode of the transistor connected; and a power supply terminal of the switching control IC connected to a cathode electrode And a Zener diode in which a base electrode and a cathode electrode of the transistor are connected, and an anode electrode is connected to a low-potential output line of the rectifier circuit. A zener connected between the base electrode of the transistor and the low potential side output line. When the potential of the base electrode of the transistor becomes constant by the Zener voltage value set by the diode, the DC voltage supplied from the auxiliary coil of the transformer to the power supply terminal of the switching control IC is compensated. Switching power supply circuit.