JPH0747994Y2 - High voltage power supply circuit - Google Patents

Description

[Detailed Description of the Invention] <Description of the Field to which the Invention belongs> The present invention is a television or a CRT equipped with a flyback transformer.
The present invention relates to a high-voltage power supply circuit suitable for supplying power to a display or the like.

<Description of Prior Art> FIG. 1 is a conventional circuit diagram of this type, which will be described below with reference to the drawings. In the figure, E is a DC input power supply, Q ₁ is a main switch element (eg transistor) connected between power supplies E, and T ₁ is 1
The chopper transformer having the secondary winding N ₁ and the secondary winding N ₂ constitutes the converter main circuit D / D as described above. Next, C ₂ is an input capacitor charged by the output of the converter D / D, T ₂ is a flyback transformer and is connected to the primary winding N ₄ connected to the input capacitor C ₂ and the primary winding N ₄ . Boosted winding N
₃ and secondary winding N ₅ and feedback winding N to which high voltage load HR is connected
Equipped with ₆ .

Q ₄ is a switch (horizontal deflection transistor) that turns on / off the voltage of the primary winding N ₄ by a signal from the horizontal synchronizing circuit SC, etc., and then B is a booster circuit together with a capacitor C ₄ and a rectifying diode D _3. They form a parallel circuit and are connected between the boost windings N ₃ . T ₃ is a base transformer, the primary winding N 7 is connected between the feedback winding N ₆ of the flyback transformer T ₂ through the rectifying diode D ₄ , and the secondary winding N ₈ is connected through the diode D ₁ to the main switching element Q ₁ Of the main switch element Q _{1 and} the constant voltage circuit CV which will be described later. Next, in the constant voltage circuit CV, C ₅ and R ₃ , R ₄ are capacitors and resistors for detecting the voltage of the input capacitor C ₂ , Q ₂ is a transistor, D _Z is a constant voltage diode, and Q ₃ is a base current bypass transistor. Is. Main transistor Q ₁ Operation of the circuit is a DC power supply E is turned on through the starting resistor R ₁
A base current flows through the main transistor and activates it, the main transistor Q ₁
ON operation by charged如Mel input capacitor C ₂ to a shown polarity through the primary winding N ₁ of the chopper transformer T _1. At the same time, the voltage generated in the secondary winding N ₂ of the chopper transformer forward biases the base and emitter of the transistor Q ₁ via the capacitor C ₁ and the resistor R ₂ . Therefore the transistor
When Q ₁ reaches the collector current IC which can be supplied by the base current flowing in the path of the starting resistance R ₁ and the secondary winding N ₂ → capacitor C ₁ → resistance R ₂ , the main transistor Q ₁ is turned off. Then, again, the base current from the starting resistor R ₁ causes the main transistor
Q ₁ works on. Repeating this operation causes the main transistor Q ₁ to oscillate and further charge the input capacitor C ₂ .

On the other hand, in a high voltage load HR such as a television and a CRT display connected to the secondary winding N ₅ side of the flyback transformer T ₂ , an input that is a high impedance load when the horizontal deflection circuit SC is not operating. The voltage of the capacitor C ₂ rises further. (In this case, transistor Q ₄ is off)
When the voltage of the input capacitor C ₂ rises and reaches a predetermined value, the horizontal deflection circuit SC operates by a horizontal signal (not shown), and in synchronism with this, a current flows through the base of the horizontal deflection transistor Q _{4 and} the transistor Q ₄ is turned on. ₄ turns on.

As a result, the collector current of the transistor Q ₄ flows in the primary winding N ₄ of the flyback transformer. On the other hand, at this time, the secondary winding N ₅
Since the voltage shown in the figure occurs, the high voltage diode D ₀ is in the off state. Therefore, electric charges are accumulated in the flyback transformer during this period. Then, when the transistor Q ₄ is turned off, the high voltage diode is forward biased, and the stored energy is supplied to the load R _L via the high voltage capacitor C ₀ .
Further, the voltage of the polarity shown in the step-up winding through the primary winding N ₄ during ON of the transistor Q ₄ is caused to charge the path capacitor C ₄ of the capacitor C ₄ → diode D _3. Therefore, the voltage of the capacitor C ₄ functions as a booster for obtaining the specified voltage even when the voltage of the input capacitor C ₂ drops. When the transistor Q ₄ is turned on, a voltage is generated in the feedback winding N ₆ , and this voltage is applied to the base of the main transistor Q ₁ via the primary winding N ₇ and the secondary winding N ₈ of the base transformer T _3. is applied, thereby the main transistor Q main transistor Q ₁ is supplied sufficient base current to ₁ perform a stable oscillation operation. On the other hand, when a sufficient base current is supplied to the main transistor Q ₁ , the voltage of the input capacitor C ₂ rises, and the voltage of the capacitor C ₅ of the constant voltage circuit CV rises accordingly, which exceeds the specified (output voltage). Then, the transistor Q ₂ and the constant voltage diode D _Z are turned on via the voltage dividing resistors R ₃ and R ₄ , and the transistor Q ₃ is turned on. As a result, the base current of the main transistor Q ₁ is shunted to perform constant voltage control of the output voltage (voltage of the capacitor C ₂ ).

<Problems of Prior Art> In the above conventional circuit, the horizontal deflection circuit does not completely stop due to the energy stored in the capacitor C _{2 of the} booster circuit in the case of load short circuit. Transistor Q ₄ works. Therefore, a voltage may be generated in the feedback winding N ₆ and the main transistor Q ₁ may be turned on via the base transformer T ₃ and destroyed.
Further, in the constant voltage circuit CV, the base current of the main transistor Q ₁ is directly supplied from the feedback winding N ₆ , and this is absorbed by the auxiliary transistor Q ₃ to be controlled. There is a drawback that the loss of the base circuit becomes large because the base current supply to the main transistor Q ₁ cannot be limited when it is desired to reduce the supply of the base current when the load is light.

<Purpose of the Invention> The present invention aims to provide a high-voltage power supply circuit that protects the main switching element when a load is short-circuited and reduces the loss of the base circuit (trigger circuit) of the main switching element.

<Structure of Device> FIG. 2 is a circuit diagram of an embodiment of the present invention, and the same reference numerals as those in the conventional circuit indicate the same parts. The main component of the present invention is to provide a control transistor Q ₅ between the feedback winding N ₆ and the base power supply (driving source) of the transistor Q ₅ via the resistor R ₅ to the output of the converter circuit, that is, the output of the capacitor C ₂ . And the auxiliary transistor Q ₃ of the constant voltage circuit is connected to the base of the control transistor Q ₅ .

<Operations and effects of the device> The operation of the circuit of the present invention is basically the same as the conventional example and is omitted. However, in the constant voltage circuit CV, when the converter output is within the specified value, the transistors Q ₂ and Q ₃ are in the off state. Is. Therefore, the control transistor Q ₅ is turned on via the resistor R ₅ , and the main transistor Q ₁ is oscillated by being supplied with the base current via the transformer T ₃ . On the other hand, when the voltage exceeds the specified value, the transistors Q ₂ and Q ₃ are turned on, the control transistor Q ₅ is turned off, the base current of the main transistor Q ₁ is cut off, and this is turned off to perform a constant voltage function. On the other hand, when the load is short-circuited, even if energy is stored in the capacitor C ₄ of the booster circuit B, the voltage across the capacitor C ₂ drops to almost zero potential, so the control transistor Q ₅ turns off and the main transistor Q ₁ As a result of shutting off the base current to the transistor, the main transistor can be surely turned off. Hence the main transistor Q ₁ is on when the output is short-circuited according to the present invention can be completely turned off can prevent breakage of the main transistor Q _1, also connect the auxiliary transistor Q ₃ of the constant-voltage control to the base of the main transistor Q ₅ In order to control this, the base current of the main transistor Q ₁ can be limited via the control transistor Q ₅ at the time of high input voltage or light load, which is advantageous in that loss of the base circuit can be reduced. .

Next, FIG. 3 is a circuit diagram of another embodiment of the present invention. In the above embodiment (FIG. 2), an example in which a chopper type converter is applied as a converter circuit has been described. In FIG. 3, a ringing choke converter is applied. Here is an example. With this, almost the same effect can be obtained.

As is apparent from the above description, the present invention can provide a high-voltage power supply circuit suitable for a power supply of a television, a CRT display or the like, and has a great practical effect.

[Brief description of drawings]

FIG. 1 is a conventional circuit diagram, and FIGS. 2 and 3 are circuit diagrams of an embodiment of the present invention. In the figure, E is the DC input power supply, Q ₁ is the main switching element, T ₂ is the chopper transformer, T ₂ is the flyback transformer, T ₃ is the base transformer, C ₂ is the input capacitor, and D / D.
Is a converter circuit, B is a booster circuit, HR is a high voltage load,
Q ₄ is a switch (horizontal synchronizing transistor) SC is a horizontal synchronizing circuit, and Q ₅ is a controlling transistor.

Claims (3)

[Scope of utility model registration request] 1. A converter circuit (D / D) for charging an input capacitor (C ₂ ) by turning on and off a main switch element (Q ₁ ) connected between a DC power source (E), and the input capacitor (D). C ₂₎ 1 winding (N ₄ between) is connected, a secondary winding and (N ₅₎ side flyback transformer (T ₂ where high-pressure load (HR) is connected to), the one Tsugimaki Step-up winding (N ₃ ) connected to the line (N ₄ ), booster circuit (B) connected between the step-up windings, and switch (Q ₄ ) for turning on / off the primary winding voltage And a control circuit (CON) for turning on and off the main switch element (Q ₁ ) by being fed by the feedback winding (N ₆ ) provided in the flyback transformer (T ₂ ).
In high-voltage power supply circuit including bets, said feedback winding (N ₆₎ the converter circuit wherein the control switch (Q ₅₎ provided with a control switch (Q ₅₎ between (D / D) of the output voltage The high-voltage power supply circuit is characterized by being driven by. 2. A high voltage power supply circuit according to claim 1, wherein a chopper type boost converter is used as the converter circuit. 3. A high-voltage power supply circuit according to claim 1, wherein a ringing choke converter is used as the converter circuit.