KR840002469B1 - Power circuit - Google Patents

Abstract

A power supplier provides constant output voltage in response to the variable input voltage of 80-270 V. The power supplier consists of a bridge rectifier (1), a switching circuit (2) drived by a switching Tr. (TR11), a chopper transformer circuit (3), a full wave rectifier (4) which output is connected to the base of the TR11, and a control circuit (5) connected to the circuit (3). The base of switching Tr. (TR11) is also connected to the output of the control circuit (5) and the input of the trigger (e).

Description

Chopper type automatic conversion power supply circuit

1 is a circular chopper-type power circuit diagram.

2 is a conventional chopper-type power supply circuit diagram.

3 is a circuit diagram of the present invention.

4 is a waveform diagram of the present invention.

* Explanation of symbols for main parts of the drawings

1: bridge rectification circuit part 2: switching circuit part

3: chopper transformer circuit part 4: onion back pressure rectifier

5: Error detection and control circuit

DI: Fly Wheel Diode

e, f: Trigger pulse input terminal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for application to an electronic device such as a television receiver, and in particular, a chopper type automatic conversion power supply capable of automatically adjusting a constant DC output voltage in response to a wide range of inputs of commercial AC voltages of 80V to 270V. It is about a circuit.

FIG. 1 shows a circular chopper circuit that is the basis of a switching mode power supply (SMPS) circuit among conventional chopper circuits, and it is difficult to control the main switching transistor TR1. Since it is not easy and requires a separate oscillation circuit and an aftershock transformer for excitation, the circuit configuration is complicated and the manufacturing cost is relatively high.

FIG. 2 shows an example of a circuit that has been actually used in the prior art. Instead of the excitation transformer for exciting the juice switching transistor TR1, the transistor L1 is inductively coupled to the winding L1 by a separate winding L3. In order to easily control the transistor TR1, a separate winding L2 is inductively coupled to the winding L1 so that the winding L1 is switched off when the transistor TR1 is switched off. The difference between the circuit of FIG. 1 and FIG. 1 is that the accumulated energy generated in the above is induced in the winding L2 and transferred to the output shaft through the flywheel diode D1.

However, in the switching method such as the circuit of FIG. 2, since the accumulated energy generated in the winding L1 is induced in the winding L2 and transmitted to the output shaft, the conversion efficiency of the switching transformer L1 is very high. It is accompanied by a tricky condition that it must be done. In addition, the coupling degree between the winding (L1) and the winding (L2) has to be a high tight coupling in order to improve its transformation efficiency, which has a great difficulty in manufacturing and manufacturing the transformer (T1).

In addition, no matter how good the coupling degree is, the coupling degree of 100% is impossible and the loss of efficiency of the entire power supply circuit is relatively low due to the denaturation loss. Since the instantaneous impulse is applied to the collector when switching off, the risk of breakage increases unless the breakdown voltage between the collim emitters of the transistor TR1 is set to a large value.

The present invention eliminates the drawbacks of the conventional chopper-type power conversion circuit as described above. Instead of a separate self-oscillating circuit or an aftershock transformer, a choke-type transformer (T11) is used and the installation of the switching transformer (T1) is eliminated. It is an object of the invention to improve the conversion efficiency and to reduce the manufacturing cost while miniaturizing the device.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

The present invention connects the switching circuit unit 2 driven by the switching transistor TR11 to the conventional bridge rectifier circuit unit 1 and switches the output stage of the onion back voltage rectifying unit 4 inductively coupled with the chopper transformer circuit unit 3. The error detection and control circuit unit 5 connected to the base of the transistor TR11 and the output terminal of the control circuit unit 5 and the trigger pulse input terminal e are connected to the base of the switching transistor TR11. It is.

Reference numeral D11 denotes a flywheel diode, a and b denote AC input terminals, and g and h denote DC constant voltage output terminals.

FIG. 3 shows a specific circuit diagram of the present invention having the above-described structure. When an arbitrary commercial AC voltage in the range of 80 V to 270 V is input between the AC input terminals (a) and (b), the AC voltage is converted into a switch (SW) and a fuse. It is applied to the normal bridge rectifier circuit portion 1 through the smoothing capacitor (C11) is charged with a DC voltage. This voltage is a DC voltage that includes pulsating components due to the power frequency. The AC input fluctuates in the range of 100V to 360V as the AC input varies from 80V to 270V, which is about 15.75 when applied to television. By switching the switching transistor TR11 of the switching circuit section 2 by pulse width modulation method to KHz or 15.625KHz, the pulsation voltage is output terminal across the output voltage smoothing capacitor C13. Between (g) and (h), it is converted into a constant voltage DC output voltage.

Here, the switching operation of the switching transistor TR11 is performed as follows. That is, the base current IBO first flows to the base of the switching transistor TR11 through the starting resistor R11 due to the voltage charged in the smoothing capacitor C11. As a result, an amplifying current of the switching transistor TR11 flows in the winding L11, and the collector current IC of the transistor TR11 increases exponentially. If the voltage at both ends of the winding (L11) at this time, ep,

가 된다.

Becomes

However, Lp denotes an inductance of the winding L11, and I _D denotes a current flowing to the diode D11 through the winding L11.

At the same time, a voltage is generated at both ends of the secondary winding L13 of the transformer T11 in proportion to the secondary and primary winding ratios n2 / n1.

가 된다.

Becomes

는 권선비, Lp는 권선(L11)의 인덕턴스, IC는 스윗칭 트랜지스터(TR11)의 콜렉터전류, I _D 는 다이오드(D11)로 흐르는 전류를 표시한다.only,

Is the winding ratio, Lp is the inductance of the winding L11, IC is the collector current of the switching transistor TR11, and I _D is the current flowing through the diode D11.

This voltage es is boosted by onion back pressure rectification by the diode D14 and the capacitor C12 of the onion back pressure rectifier 4, and is connected in parallel with the series circuit of the resistor R13 and the capacitor C14. The base current IB of the switching transistor TR11 is increased through the resistor R12. Here, the base current IB of the transistor TR11 is

가 된다.

Becomes

However, the voltage at both ends of the es non winding L13 is shown.

Therefore, the base current IB becomes a substantially constant value, so that a current having a waveform as shown in (4) of FIG. 4 flows. At this time, the base current of the switching transistor TR11 rises from the first IBO to a constant value of IB because it is caused by the positive feedback through the transformer T11, and thus the current flowing through the base of the transistor TR11. Will rise momentarily. At this time, the voltage VCE between the collector and the emitter of the switching transistor TR11 becomes almost zero. Here, the series circuit of the resistor R13 (and the capacitor C14) operates to increase or decrease the speed of the base current IB. When the DC current amplification ratio of the switching transistor TR11 is h _FE The maximum value of the collector current IC of the switching transistor TR11 is

은 0으로 되고, 따라서 2차권선(L13)의 양단 유기전압도 0으로 된다. 이에 따라 베이스전류(IB)는 급격히 감소되고 콜렉터전류(IC)도 급격히 감소되어 결국 전류변화율

은 부(負)가 되기에 이르며, 2차권선(L13)에 발생하는 전압도 부(負)로 되어 스윗칭 트랜지스터(TR11)의 베이스에 역바이어스가 가해져서 스윗칭 트랜지스터(TR11)를 컷오프(Cut OFF)시킨다. 이때 콜렉터 전류(IC)는 순간적으로 0으로 떨어지게 된다.IC = h _FE · IB and no more flow. This is because the base current IB of the switching transistor TR11 is maintained at a constant value as described above. Thus, if there is no increase in the current IC at IC = h _FE · IB, the current change rate of the primary winding (L11)

Becomes 0, and therefore, the induced voltage across the secondary winding L13 also becomes zero. Accordingly, the base current IB is drastically reduced and the collector current IC is also drastically reduced, resulting in a current change rate.

Becomes negative, and the voltage generated in the secondary winding L13 is also negative, and a reverse bias is applied to the base of the switching transistor TR11 to cut off the switching transistor TR11. Cut OFF). At this time, the collector current IC instantaneously falls to zero.

The energy E accumulated in the winding L11 by the cut-off state of the switching transistor TR11 is

이 된다.

Becomes

Where Lp is the inductance of the winding L11, and IC is the collector current of the switching transistor TR11.

This energy E is caused to flow through the flywheel diode D11 to be discharged toward the load. When the current I _D flows through the diode D11, the reverse voltage is generated in the winding L13 during the period of (t1) to the time t3, so that the switching transistor TR11 is cut off. Becomes After the time t3 at which the energy is released, the initial base current IBO of the switching transistor TR11 flows again by the starting resistor R11, and the self-oscillation described above is started again. The operation will be repeated.

Although the above description shows the operating state under the free oscillation state without the trigger pulse input at the base of the switching transistor TR11, the trigger pulse input terminal (e) (f) as shown in FIG. When the power supply is supplied between the transistors R1 and D13, the base of the switching transistor TR11 is triggered through the resistor R19 and the diode D13, so that synchronous oscillation is possible at a constant frequency. The current I _C + I _D flowing through the winding line L11 becomes as shown in FIG. 8 (8).

Therefore, the free oscillation frequency is set to be longer than the period of the trigger pass for external synchronization.

The trigger pulse used here can be obtained by winding an insulated winding on the secondary side of an FBT (Fly Bac Transformer).

As described above, when the switching transistor TR11 performs a switching operation, the output smoothing capacitor C13 is charged by the collector current IC and the current ID of the diode D11, and the DC voltage is output to the load side. It is possible to supply between the terminals g and h. At this time, however, when the AC input voltage between the AC input terminals (a) and (b) changes or the load condition on the load side connected between the output terminals (g) and (h) changes, the DC output voltage does not maintain a constant voltage. Done. The circuit portion for maintaining the constant output DC voltage consists of a zener diode D12, resistors R14, R15, R16, R17, R18, and transistors TR12, TR13. Circuit 5.

For example, when the output voltage between the output terminals g and h rises, the potential difference between the base and the emitter of the transistor TR13 increases, so that the base current flows. Accordingly, the transistor (through Zener diode D12) causes the transistor ( The collector current flows through TR13, which becomes the base current of the transistor TR12 through the resistor R18. Therefore, the transistor TR12 shunts the base current IB of the switching transistor TR11. The flow of the collector current IC of the transistor TR11 is stopped, and the flow of the current ID of the diode D11 is stopped, and as a result, the output DC voltage between the output terminals g and h is lowered. If the output voltage falls below the specified value, the operation opposite to the above description is performed, and the output voltage rises, and the resistor R14 is a resistor for the basic current shunt of the zener diode D12 and the zener diode D12. It serves to maintain a constant voltage across the.

이 작아지므로 기간(t0~t1)이 길어 지게 되고, 교류 입력전압이 높아지면 전류변화율

이 커지게 되므로 기간(t0~t1)을 짧아지게 된다. 즉, 입력교류전압의 고저(高低)와 출력측의 부하 변동에 따라서 스윗칭 트랜지스터(TR11)의 스윗칭 동작의 듀리 사이클(Duty cycle)이 변동하게 된다.As described above, according to the present invention, the switching operation is performed by external synchronization pulses having a constant period t0 to t2.

Since the period becomes small, the period (t0 to t1) becomes long, and when the AC input voltage increases, the current change rate

Since this becomes large, the period t0 to t1 is shortened. That is, the duty cycle of the switching operation of the switching transistor TR11 varies according to the high and low input AC voltage and the load variation on the output side.

From this, the switching transistor TR11 performs a switching operation in the form of pulse width modulation, thereby eliminating pulsating components and voltage fluctuations caused by the AC frequency in the output DC voltage, thereby obtaining a pure DC constant voltage output. Will be.

As described above, in the present invention, since the secondary side winding for oscillation is added to the choke coil CHI of the circular chopper circuit as shown in FIG. 1 and used as the choke and transformer T11, a switching transistor ( The self-oscillation of TR11 is made possible, thus eliminating the need for a separate oscillation circuit or an excitation transformer and accumulating in the winding L11 when the switching transistor TR11 is cut off. Since the discharged energy is directly discharged to the load side through the flywheel diode (D11), there is an advantage in that the conversion efficiency can be improved with high efficiency without the loss of denaturation.

That is, although the conversion efficiency (output ratio of DC output power to AC input power) of the conventional method as shown in FIG. 2 is about 80%, the present invention can improve the conversion efficiency by about 90 to 95%.

On the other hand, since the conversion efficiency is higher than that of the conventional method and the secondary winding for modifying energy accumulation (no need to install the winding L2 in the conventional transformer T1), the chopper transformer T11 can be miniaturized and the device weight can be reduced. Moreover, in the conventional method, if the induction tight coupling degree between the winding L1 and the winding L2 is not maintained, the conversion efficiency of accumulated energy becomes worse. Therefore, a very difficult problem in the manufacture of the chopper transformer is required to obtain the induction tight coupling degree. Accompanying this, in the present invention, it does not use a type of chopper transformer, thereby reducing the manufacturing cost.

Further, in the conventional switching transistor TR1, when the inductive coupling degree between the primary winding L1 and the secondary winding L2 of the chopper transformer T1 is incomplete, the primary winding L1 of the chopper transformer T1. Since an impulse voltage is generated at the power supply), a switching transistor TR1 having a high maximum rating of the power VCE between the collector and the emitter has to be used. However, in the present invention, a switching emitter between the collector transistors of the switching transistor TR11 is used. Since a high voltage above the charging voltage of the smoothing capacitor C11 is not applied, a transistor having a relatively low maximum rating may be used.

Claims (1)

A switching transistor (TR11) is connected to a switching circuit (2) connected to a switching circuit (2) driven by a switching transistor (TR11) to a conventional bridge rectifier circuit (1) and inductively coupled to the chopper transformer circuit (3). Chopper connected to the base of the chopper transformer circuit part 3 and connected to the base of the switching transistor TR11 with the output terminal of the control circuit part 5 and the trigger input terminal e connected to the base of the switching transistor TR11. Type automatic conversion power circuit.

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