KR940001275Y1 - High voltage power supply circuit - Google Patents

Abstract

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Description

High voltage power circuit

1 is a conventional high voltage power supply circuit diagram.

2 is an embodiment circuit diagram of the present invention.

3 is a circuit diagram of an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

Q1: main switch element T2: flyback transformer

C2: input capacitor D / D: converter circuit

B: Booster Circuit HR: High Pressure Load

SC: Horizontal Synchronization Circuit Q5: Control Transistor

The present invention relates to a high voltage power supply circuit suitable for supplying a voltage to a television or a CRT display having a flyback transformer.

FIG. 1 is a conventional circuit diagram of this kind, which will now be described with reference to the drawings. In the figure, E is a DC input power supply, Q1 is a main switch element (eg transistor) connected between the power source E, and T1 is a chopper transformer having a primary winding N1 and a secondary winding N2 to constitute a converter main circuit D / D. C2 is an input capacitor charged by the output of converter D / D, T2 is a flyback transistor, primary winding N4 connected to input capacitor C2, boost winding N3 connected to this primary winding N4, and high voltage load. The secondary winding N5 and the feedback winding N6 to which HR are connected are provided. Q4 is a switch (horizontal deflection transistor) for turning on and off the voltage of the primary winding N4 by a signal from a horizontal synchronizing circuit SC, etc., and then B is a booster circuit, and a parallel circuit is formed with a capacitor C4 and a rectifier diode D3. It is formed and connected between boost winding N3.

T3 is a base transformer connected to the primary winding N7 through the rectifying diode D4 between the return winding N6 of the flyback transformer T2, and the secondary winding N8 is connected to the base of the main switch element Q1 via the diode D1, which will be described later. The control circuit CON of the main switch element Q1 is formed together with the constant voltage circuit CV.

Next, in the constant voltage circuit CV, C5, R3 and R4 are voltage detecting capacitors and resistors of the input capacitor C2, Q2 is a transistor, DZ is a constant voltage diode, and Q3 is a base current path transistor.

The operation of this circuit shows the input capacitor C2 through the primary winding N1 of the chopper transformer T1 by the on-operation of the main transistor Q1, which, when the DC power supply E is applied, causes the base current to start to the main transistor Q1 via the movable resistor R1. Start charging to the polarity. At the same time, the base and emitter of the transistor Q1 are forward biased through the capacitor C1 and the resistor R2 by the voltage generated in the secondary winding N2 of the chopper transformer. Therefore, when the transistor Q1 reaches the collector current IC through which the base current can pass through the path of the movable resistor R1 and the secondary winding N2? Condenser C1? Resistor R2, the main transistor Q1 transitions to the off state.

Therefore, the main transistor Q1 is turned on again by the base current from the movable resistor R1. By repeating this operation, the main transistor Q1 enters the oscillation state and charges the input capacitor C2 again.

On the other hand, in a high-voltage load HR such as a television and a CRT display part connected to the secondary winding N5 side of the flyback transformer T2, when the horizontal deflection circuit SC is not in operation, the voltage of the input capacitor C2 increases further because it is a high impedance load ( In this case transistor Q4 is off). Therefore, when the voltage of the input capacitor C2 rises and reaches a predetermined value, the horizontal deflection circuit SC is operated by a horizontal signal (not shown), and this transistor Q4 is turned on through a current in the base of the horizontal deflection transistor Q4 in synchronization with this. .

As a result, the collector current of transistor Q4 passes through the primary winding N4 of the flyback transformer. Meanwhile, at this time, since the voltage shown in the secondary winding N5 is generated, the high voltage diode D0 is in an off state. Therefore, charges accumulate in the flyback transformer. Therefore, when transistor Q4 is turned off, the high voltage diode is forward biased, and the accumulated energy is supplied to the load RL via the high voltage capacitor C0. When the transistor Q1 is turned on, a voltage is generated at the polarity shown in the boost winding through the temporary winding N4 to charge the path capacitor C4 from the capacitor C4 to the diode D3. Therefore, the voltage of this capacitor C4 functions as a booster for obtaining a specified voltage even when the voltage of the input capacitor C2 decreases. Further, when the transistor Q4 is turned on, a voltage is generated in the feedback winding N6, and this voltage is applied to the base of the main transistor Q1 via the primary winding N7 and the secondary winding N8 of the base transformer T3, thereby applying it to the main transistor Q1. Sufficient base current is supplied so that the main transistor Q1 has stable oscillation. On the other hand, when a sufficient base current is supplied to the main transistor Q1, the voltage of the input capacitor C2 increases, and with this, the voltage of the capacitor C5 of the constant voltage circuit CV rises, and when this exceeds the specified value (output voltage), the voltage divider R3, Transistor Q2 and constant voltage diode DZ conduct via R4 to turn on transistor Q3. As a result, the base current of the main transistor Q becomes the axis, and performs constant voltage control of the output voltage (capacitor C2 voltage).

In the above-described conventional circuit, in the case of a load short circuit, the horizontal deflection circuit does not stop completely by the energy accumulated in the capacitor C2 of the booster circuit, so that the horizontal deflection transistor Q4 operates repeatedly or intermittently. This may generate voltage in the feedback winding N6, turn on the main transistor Q1 via the base transformer T3, and destroy it. In the constant voltage circuit CV, in order to directly supply the base current of the main transistor Q1 from the feedback winding N6, and to absorb and control this by the auxiliary transistor Q3, to the main transistor Q1 at high input voltage or light load. When it is desired to reduce the base current supply, this cannot be limited, resulting in a large loss of the base circuit.

This invention aims at providing the high voltage power supply circuit which aimed at protecting the main switch element at the time of a load short circuit, and reducing the loss of the base circuit (trigger circuit) of the main switch element.

2 is a circuit diagram of an embodiment of the present invention, in which portions identical to those of the conventional circuit are denoted by the same reference numerals. The main component of the present invention is to provide a control transistor Q5 between the feedback winding N6 so that the base power supply (drive source) of the transistor Q5 is obtained from the splitting point P of the divided voltage resistors R3 and R4 for output detection of the converter circuit via the resistor R. And the auxiliary transistor Q3 of the constant voltage circuit are connected to the base of the control transistor Q5.

Since the operation of the circuit of the present invention is basically the same as in the conventional example, it is omitted. However, in the constant voltage circuit CV, the transistors Q2 and Q3 are turned off when the converter output is within a specified value. Therefore, the control transistor Q5 is turned on via the resistor R5, and the main transistor Q1 is oscillated by the base current supplied through the transformer T3. On the other hand, if it exceeds the prescribed value, the transistors Q2 and Q3 are turned on and the control transistor Q5 is turned off to cut off the base current of the main transistor Q1, and turn it off to fulfill the constant voltage function. On the other hand, at the time of the load short circuit, even when energy is accumulated in the capacitor C4 of the booster circuit B, the voltage across both capacitors C2 decreases to almost zero potential, so that the control transistor Q5 is turned off due to the potential drop at the split point P, and thus the voltage is reduced to the main transistor Q1. As a result of cutting off the base current, this main transistor can be reliably turned off. Therefore, the main transistor Q1 can be completely turned off during an output short circuit, so that the main transistor Q1 can be prevented from being destroyed, and the auxiliary transistor Q3 for constant voltage control is connected to the base of the main transistor Q5 to control it. At high input voltages or light loads, the base current of the main transistor Q1 can be limited via the control transistor Q5, thereby reducing the loss of the base circuit.

Since the output voltage detection of the converter is detected by dividing the voltage divider resistors R3, R4, R7, and R8, the transistor Q2 and the constant voltage diode DZ for voltage detection are used with low voltage.

Next, FIG. 3 illustrates an example in which a chopper type converter is used as the converter circuit in the above embodiment (Fig. 2) in an embodiment circuit diagram other than the present invention, but FIG. 3 shows an example in which a ringing choke converter is applied. By this, almost the same effect can be obtained.

As apparent from the above description, according to the present invention, a high-voltage power supply circuit most suitable for power supply of a television or a CRT display unit is provided, and the practical effect is large.

Claims (3)

The primary winding N4 between the converter circuit D / D for charging the input capacitor C2 by the on / off operation of the main switch element Q1 connected to E between the DC power supplies and the above-described input capacitor C2. ) Is connected to the flyback transformer T2 to which the high-pressure load HR is connected to the secondary winding N5 side, the boost winding N3 connected to the primary winding N4, and the above-mentioned boosting voltage. The main circuit described above is supplied with a booster circuit B connected between windings, a switch Q4 for turning on and off the primary winding voltage, and a feedback winding N6 provided in the flyback transformer T2. In the high-voltage power supply circuit having a control circuit CON for operating the switch element Q1 on and off, a control switch Q5 is provided between the feedback winding N6 and the transducer output voltage is detected. The voltage divider resistors R3 and R4 are provided so that the control switch Q5 is driven by the voltage at the voltage dividing point of the voltage divider resistor. High voltage power supply circuit characterized in that. The high voltage power supply circuit according to claim 1, wherein a chopper type boost converter is used as the converter circuit. The high voltage power supply circuit according to claim 1, wherein a ringing choke converter is used as the converter circuit.