JPH0382368A - Self-exciting switching power supply - Google Patents

Abstract

PURPOSE:To obtain a high frequency circuit by superposing the voltage, which is obtained by rectifying the voltage generated in the auxiliary winding of a transformer where DC voltage is applied to the primary winding through an FET, on the starting voltage made of DC voltage at the gate of FET. CONSTITUTION:DC voltage D is applied to the primary winding of a transformer 41 through an FET 43 from terminals 60 and 61. FET 43 starts up the gate, being energized with the value of the voltage divided by resistances 55 and 56. The form and voltage generated in an auxiliary winding 41C is superposed on the gate of FET 43, through a diode 50, a resistance 57, and a capacitor 54. Moreover, a capacitor 45 is charged with the reverse voltage of the auxiliary winding 41C, and when the voltage exceeds over the Zener voltage of a Zener diode ZD53, ZD53 becomes ON, and transistors 48 and 49 also become ON, and lower the gate voltage of FET43 suddenly and turns off FET43. After that, FET43 is turned on again by the voltage of resistances 55 and 56, and repeats this operation. Hereby, a high frequency circuit is obtained, and the efficiency improves.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a self-excited switching power supply circuit such as a DC/DC converter.

[Conventional technology]

Conventionally, as a self-excited switching power supply circuit, a C/DC converter as shown in Figs. 3 and 4 was used.
(March 1997), etc.

The DC/DC converter shown in Figure 3 has a primary winding 11a.
.

A transformer 11 having a secondary winding 11b and an auxiliary winding 11c
゜Switching transistor 12, capacitor 13-1
It is composed of 5° diodes 17 to 19, resistors 20 and 21, and a Zener diode 22.

When a DC voltage Vin is applied between the terminals 23 and 24, a starting current flows through the starting resistor 21 to the base of the transistor 12 due to the DC voltage Vin.
turns on. Therefore, current flows through the transistor 12 to the primary winding 11a of the transformer 11 due to the DC voltage Vin, and the secondary winding 11b of the transformer 11 flows.

A forward voltage is induced in the assistant 1i11c. The forward voltage induced in the auxiliary winding 11c causes a base current to flow through the parallel circuit of the diode 18 and the capacitor 14 and the resistor 20 to the base of the transistor 12, and this base current Ib
Let Rb be the resistance value of the resistor 20, NP and Nb be the number of turns of the primary winding 11a and the auxiliary winding 11c of the transformer 11, Vf be the forward voltage of the diode 18, and Vba be the voltage between the base and emitter of the transistor 12. This becomes a constant current Rb. The collector current Ic of the transistor 12 increases due to this base current rb, but
When the DC current amplification factor Hfe of the transistor 12 reaches Rb, the transistor 12 cannot maintain an on state, that is, the base current is insufficient and the transistor 12 shifts to the active region, and the collector voltage increases. As a result, the voltage of the primary winding 11a of the transformer 11 decreases, the voltage of the auxiliary winding 11c decreases, and the base current of the transistor 12 becomes further insufficient.
Transistor 2 suddenly turns off. transistor 12
At the moment when the transformer 11 is turned off, a back electromotive force is generated in the secondary winding 11b and the auxiliary winding lie, and the voltage induced in the secondary winding 11b is converted into a DC voltage by the diode 19 and the capacitor 15 and output. be done. Also, capacitor 1
3 is charged through the diode 17 by the back electromotive voltage induced in the auxiliary winding 11c. The above operation is repeated, and when the transistor 12 is turned on, the capacitor 13
When the voltage VC reaches Vc=Vz+Vbe (Vz is the Zener voltage of the Zener diode 22), the Zener diode 22 becomes conductive and the current from the auxiliary winding 11c of the transformer 11 to the base of the transistor 12 flows to the Zener diode 22 side. , transistor 12 is turned off. The period during which current flows through the capacitor 13 is the same as the period during which the induced voltage in the secondary winding 11b of the transformer 11 is output through the diode 19, so the output voltage and the capacitor 1
The output voltage is made constant in proportion to the charging voltage Vc of No. 3.

The DC/DC converter shown in Figure 4 has a primary winding 11a.
.

A transformer 11 having a secondary winding 11b and an auxiliary winding 11c
゜Transistors 12, 25, capacitors 13 to 15, 2
6, diodes 17-19, resistors 20, 21, 27-2
9, a photocoupler consisting of a Zener diode 22, a light emitting diode 30, and a phototransistor 31, and a programmable shunt regulator 32.

When the DC voltage Vin is applied between the terminals 23 and 24, the transistor 1
2 is turned on/off to obtain an output voltage, but the operation for regulating the output voltage is different from that of the DC/DC converter shown in FIG. That is, the output voltage is divided by the resistors 28 and 29 and output to the programmable shunt regulator 3.
When the output voltage rises above the specified voltage, the cathode voltage of the programmable shunt regulator 32 decreases and the light emitting diode 30 emits light. Therefore, the phototransistor 31 becomes conductive, the transistor 25 is turned on, and the auxiliary winding 11c of the transformer 11 is turned on.
A current flows from the transistor 12 to the base of the transistor 25 to shorten the on-time of the transistor 12.

As a result, the output voltage returns to the specified voltage.

[Case 1f that the invention attempts to solve! ] In the above DC/DC converter, the time for switching on/off of the transistor 12 is longer than the time for switching on/off of the field effect transistor, so there is a problem in increasing the switching frequency of the transistor 12 to a higher frequency. However, the power loss when the transistor 12 is turned on and off is large, resulting in low efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a self-excited switching power supply circuit which can improve the above-mentioned drawbacks and can operate at high frequencies and improve efficiency.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a transformer to which a DC voltage is applied to a primary winding, a field effect transistor connected in series with the primary winding of this transformer, and a starting voltage generated from the DC voltage. a starting circuit that applies a voltage to the gate of the field effect transistor; a forward voltage application circuit that passes a forward voltage induced in the auxiliary winding of the transformer and applies it to the gate of the field effect transistor; and the auxiliary winding of the transformer. a charging circuit that is connected between the capacitor and an auxiliary winding of the transformer and charges the capacitor by passing a reverse voltage induced in the auxiliary winding of the transformer; A constant voltage circuit operates when the voltage of the capacitor reaches a certain voltage.

A collector is connected to the gate of the field effect transistor via a resistor, an emitter is connected to the source of the field effect transistor, and is operated by the operation of the voltage regulating circuit to rapidly lower the gate voltage of the field effect transistor. Accordingly, the present invention includes a transistor that increases the O'FF speed of the field effect transistor, and a DC conversion circuit that converts the voltage induced in the secondary winding of the transformer into DC.

[For production]

When a DC voltage is applied, the starting circuit turns on the field effect transistor and current flows through the primary winding of the transformer.
The forward voltage induced in the auxiliary winding of the transformer is applied to the gate of the field effect transistor by the forward voltage applying circuit, and the current in the primary winding of the transformer increases. When this current saturates, the field effect transistor cuts off and a reverse voltage is induced in the auxiliary winding of the transformer. This reverse voltage causes the charging circuit to charge the capacitor, and when the capacitor voltage reaches a certain level, the voltage regulator circuit operates and the transistor operates, causing the gate voltage of the field effect transistor to drop rapidly. It works to increase the OFF speed of field effect transistors. The voltage induced in the secondary winding of the transformer is then converted into DC by the DC conversion circuit.

〔Example〕

1st rj! I shows one embodiment of the present invention, and FIG. 2 is its timing chart.

The DC/DC converter of this embodiment has a primary winding 41a.
.

A transformer 41 having a secondary winding 41b and an auxiliary winding 41c
゜IC (integrated circuit) 42, field effect transistor 43,
It is composed of capacitors 44 to 46 and a diode 47.

IC42 is transistors 48, 49, diode 50
, 51° Zener diode 53, a capacitor 54, and resistors 55-59.

When a DC voltage is applied to the input terminal 60.61, this DC voltage is divided by the starting resistor 55.56 and applied to the gate of the field effect transistor 43, which turns on the DC voltage. transformer 41
Current flows through the field effect transistor 43 to the primary winding 41a. When the drain current to the primary winding 41a of the transformer 41 is saturated by the drain current limited by the gate voltage divided by the resistors 55 and 56, the drain current of the field effect transistor 43 rapidly decreases and is cut off. . At the moment when the field effect transistor 43 is cut off, a reverse voltage is induced in the secondary winding 41b and the auxiliary winding 41c of the transformer 41, and the diode 51 is turned on by the reverse voltage induced in the auxiliary winding 41c, and the capacitor is turned on. 45 is charged, and the capacitor 46 is also charged through the diode 47 through the secondary winding 41b. By repeating such an operation, the induced voltage of the assistant jl1141c gradually increases and reaches a voltage that is the sum of the Zener voltage of the Zener diode 53 and the base-emitter voltage of the transistor 49, and the Zener diode 53 becomes conductive. Transistor 49 is turned on, transistor 48 is turned on, and the gate voltage of field effect transistor 43 is rapidly lowered. Thereafter, the field effect transistor 43 is turned on again by the divided voltages of the starting resistors 55 and 56, and the same operation is repeated thereafter. Secondary winding Al of transformer 41
The voltage induced in I41b is rectified and smoothed by diode 47 and capacitor 46 and output as a DC voltage, and the voltage induced in auxiliary winding 41c is always a constant voltage and the output voltage is also constant.

In this embodiment, the on/off switching time of the field effect transistor 43, which has significantly less storage time than a bipolar transistor, can be shortened, making it possible to increase the switching frequency of the -a field effect transistor 43. Power loss during on/off switching of the field effect transistor 43 is small, resulting in high efficiency.

Note that the present invention is not limited to the above embodiments,
For example, it can be applied to an AC/DC converter.

〔Effect of the invention〕

As described above, the present invention includes a transformer to which a DC voltage is applied to the primary winding, a field effect transistor connected in series with the primary winding of the transformer, and a field effect transistor that generates a starting voltage from the DC voltage and generates the A starting circuit that applies voltage to the gate of a field effect transistor.

a forward voltage applying circuit that passes a forward voltage induced in an auxiliary winding of the transformer and applies it to the gate of the field effect transistor; a capacitor connected in parallel with the auxiliary winding of the transformer; a charging circuit connected between the auxiliary winding of the transformer and charging the capacitor by passing a reverse voltage induced in the auxiliary winding of the transformer; a voltage regulating circuit that operates; a collector connected to the gate of the field effect transistor via a resistor; an emitter connected to the source of the field effect transistor; and the field effect transistor is operated by the operation of the voltage regulating circuit; The transformer is equipped with a transistor that increases the OFF speed of the field effect transistor by rapidly lowering the gate voltage of the transformer, and a DC conversion circuit that converts the voltage induced in the secondary winding of the transformer into DC, making it possible to increase the frequency. and the efficiency can be increased.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a timing chart of the same embodiment, and FIGS. 3 and 4 are circuit diagrams showing conventional self-excited switching power supply circuits. 41...Transformer, 43...Field effect transistor, 44-46...Capacitor, 47...Diode, 48.49...Transistor, 50.52...Diode, 53...Zener diode , 54...
Capacitor, 55-59...Resistance.

Claims (1)

[Claims] A transformer to which a DC voltage is applied to the primary winding, a field effect transistor connected in series with the primary winding of the transformer, and a starter to generate a starting voltage from the DC voltage and apply it to the gate of the field effect transistor. a circuit, a forward voltage applying circuit that passes a forward voltage induced in an auxiliary winding of the transformer and applies it to the gate of the field effect transistor, a capacitor connected in parallel with the auxiliary winding of the transformer; a charging circuit that is connected between a capacitor and an auxiliary winding of the transformer and charges the capacitor by passing a reverse voltage induced in the auxiliary winding of the transformer; and a charging circuit that charges the capacitor until the voltage of the capacitor reaches a certain voltage. a constant voltage circuit whose collector is connected to the gate of the field effect transistor via a resistor and whose emitter is connected to the source of the field effect transistor and which is operated by the operation of the voltage constant circuit; The present invention is characterized by comprising a transistor that increases the OFF speed of the field effect transistor by rapidly lowering the gate voltage of the field effect transistor, and a direct current converting circuit that converts the voltage induced in the secondary winding of the transformer to direct current. A self-excited switching power supply circuit.