JPH1141926A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost power supply circuit superior in high-voltage stability. SOLUTION: The one end point (A) of a primary coil 7 is connected with a drive power supply 6 for connecting the other end point (B) thereof with a switching element 1. Also, a resonance capacitor 3 and damper diode 2 are connected with the point B. The cathode of a diode 4 is connected with the low-voltage side of the resonance capacitor 3 so as to connect its anode with a ground. Connecting the anode of a second diode 5 with the low-voltage side of the resonance capacitor 3, its cathode is connected via a tap with a point (C) present in the wound-down position of the primary coil 7 from the drive power supply side thereof by the voltage portion corresponding to a primary pulse voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to a power supply circuit for a flyback transformer which obtains a high voltage by boosting a resonance pulse on a primary side.

[0002]

2. Description of the Related Art In a television receiver or a display device, various power supply devices have been proposed in order to stabilize a high voltage output. Among them, a power supply device that directly controls the primary current of the flyback transformer by controlling the ON and OFF periods of the switching element according to the change in high voltage has been proposed because it can respond quickly to changes in high voltage output. ing.

Although this power supply device has the advantage of high-speed response, it has a disadvantage that unnecessary resonance pulses due to a flyback transformer and a resonance capacitor are generated during the off period of the damper period and the off period of the switching element. Was.

As means for solving this drawback, Japanese Patent No.
Japanese Patent Publication No. 531008 proposes that a clamp circuit composed of a diode is formed on the low voltage side of a resonance capacitor to suppress generation of an unnecessary pulse resonance voltage.

FIG. 4 is a circuit diagram of a power supply device according to a conventional example, and FIG. 5 is a pulse waveform diagram of each part of the power supply circuit shown in FIG. The power supply circuit shown in FIG. 4 includes a switching element 1, a damper diode 2, a resonance capacitor 3, a first diode 4 connected to the low voltage side of the resonance capacitor 3, and a second diode 4.
, And a driving power supply 6. The power supply circuit is connected to a stage preceding the primary coil 7 of the flyback transformer.

In this power supply circuit, when the switching element 1 is turned off, the current flowing through the primary coil 7 flows from the resonance capacitor 3 through the route of the second diode 5 to generate a pulse voltage. Since the low voltage side potential e3 of the resonance capacitor 3 is connected to the power supply voltage, when the switching element 1 is turned off as shown in FIG. 5, that is, when the potential e1 becomes 0 level, the off period of the switching element 1 The pulse voltage e2 generated during the first half of the pulse rises by the amount of the power supply voltage, and the pulse becomes left-right asymmetric.

[0007]

As described above, the conventional power supply circuit which forms a clamp circuit composed of a diode on the low voltage side of the resonance capacitor has a problem that the primary side pulse is left-right asymmetric. For this reason, the voltage applied to the switching element is increased by the power supply voltage, so that not only it is necessary to use an element having a high withstand voltage, but also, as a result, there is a fundamental drawback that stability against high-voltage load fluctuation is reduced. Was.

In other words, the flyback transformer boosts the primary-side pulse and rectifies it with a diode and a capacitor to generate a high voltage. At this time, the primary-side pulse is more symmetrical during the diode ON period. long. In other words, the energy stored in the capacitor is higher when the primary side pulse is more symmetrical, so that the stability against high-voltage load fluctuations is also higher. Is low.

The present invention solves the above-mentioned disadvantages of the prior art,
It is an object of the present invention to provide a low-cost power supply circuit having excellent high-voltage stability.

[0010]

According to the present invention, a drive power supply is connected to one end of a primary coil of a flyback transformer and the other end of the primary coil of the flyback transformer flows to the primary coil. A switching element that controls the current on and off and controls the on-period according to the generated high-voltage output fluctuation, a resonant capacitor that resonates with the primary coil when the switch is off, and a damper diode that supplies the damper current during the damper period are connected And
A first diode is connected between the low-voltage end of the resonance capacitor and ground, with the ground side being an anode,
The second end is connected between the connection end of the resonance capacitor and the first diode and a position tapped down by a resonance pulse voltage substantially corresponding to the drive power supply winding power supply voltage of the primary coil. It is characterized in that a diode is connected.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has the above-described configuration, and has a simple configuration in which a diode of a diode clamp circuit connected to a resonance capacitor is connected to a tap-down winding provided in a flyback transformer. In addition, the disadvantage of the conventional example that the pulse voltage becomes left-right asymmetric can be improved.

In addition, it becomes possible to use a switching element having a low withstand voltage and to provide a power supply circuit having more excellent high-voltage stability.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a basic configuration of a power supply device of the present invention. The same parts as those in the conventional example are denoted by the same reference numerals.

One end A of the primary coil 7 of the flyback transformer is connected to the drive power source 6 and the other end B is connected to the switching element 1 which is turned on and off with a change in the high voltage output. At the point B, when the switching element 1 is turned off,
A resonance capacitor 3 that resonates with the primary coil 7 and a damper diode 2 for flowing a damper current during a damper period
Connect.

A first diode 4 is provided between the low voltage side of the resonance capacitor 3 and the ground, an anode is provided on the ground side,
It connects so that the resonance capacitor 3 side may become a cathode.
Then, a second diode 5 is further connected to this connection end.

The second diode 5 has an anode connected to the resonance capacitor 3 and a cathode wound from the drive power supply of the primary coil 7 by lowering the primary winding by a voltage corresponding to the primary pulse voltage. The position C is connected via a tap to the position C.

In this configuration, when the switching element 1 is turned on, a current flows from the drive power source 6 through the primary coil 7, and electromagnetic energy is accumulated in the primary coil 7. When the switching element 1 is turned off, resonance occurs between the resonance capacitor 3 and the primary coil 7, and a pulse voltage is generated.

When the switching element 1 is turned off, the primary coil current flows from the primary coil 7 to the resonance capacitor 3, but the first diode 4 connected to the ground cuts this. Therefore, the primary coil current flows into the second diode 5 connected to the point C, and generates a pulse voltage.

At the time when the switching element 1 is turned off, the potentials of the first and second diodes 4 and 5 become equal to the primary coil 7.
To the winding potential which has been dipped down. However, since the tapped-down winding potential is set to a point that is equal to or higher than the ground potential at the time of the pulse peak and is lowered by an amount corresponding to the drive power supply voltage, the pulse voltage is a substantially symmetrical pulse.

On the other hand, when the pulse voltage becomes equal to or lower than the ground potential, a damper period starts, the damper diode 2 is turned on, and the primary coil 7 is turned on from the damper diode 2 side.
Current flows to the side.

When the damper diode 2 is turned off at the end of the damper period, the current flowing through the primary coil 7 attempts to flow through the resonance capacitor 3, but the potential across the resonance capacitor 3 becomes the power supply voltage potential. First,
The second diodes 4 and 5 cut off this, and unnecessary resonance pulses are not generated during this period.

FIG. 2 is a circuit diagram of the power supply device according to the embodiment of the present invention. FIG. 3 is a pulse waveform diagram in each part of the power supply circuit shown in FIG. 2, and the voltages e1 to e4 in FIG.
Is shown.

One end A of the primary coil 7 of the flyback transformer 8 is connected to the drive power source 6 and the other end B is connected to the FET 10 as a switching element. The FET 10 controls the current supplied to the flyback transformer 8 by changing the ON / OFF time of the switch via the PWM circuit 12 so as to stabilize the high voltage in accordance with the high voltage detection voltage extracted from the resistor 11 connected to the high voltage output. I do.

At one end B of the primary coil 7, an FET 10
Resonance capacitor 3 that resonates with primary coil 7 when
A damper diode 2 for flowing a damper current during the damper period is connected.

The first diode 4 is connected between the low voltage side of the resonance capacitor 5 and the ground so that the ground side is the anode and the resonance capacitor 3 side is the cathode. On the other hand, the primary coil 7 of the flyback transformer 8 is provided with a tap (point C) wound down on the winding side connected to the drive power supply 6. The tap position is set to be substantially equal to the drive power supply voltage.

That is, when the number of primary turns is n1, the pulse voltage generated when the FET is off is Vp, and the power supply voltage is Eb,
The number of turns n2 in the tap-down portion is n2 = n1 · Eb / Vp
And However, the peak voltage at the tap-down portion should not exceed the power supply voltage.

The anode side of the second diode 5 is connected to the connection point between the resonance capacitor 3 and the first diode 4, and the cathode side of the second diode 5 is connected to the flyback transformer 8.
Connected to the tap-down portion (point C) provided in the primary coil 7.

In this configuration, when the FET 10 is turned on, a current flows from the driving power source 6 through the primary coil 7,
Electromagnetic energy is stored in the primary coil 7.

When the FET 10 is turned off, the current flowing through the primary coil 7 flows through the resonance capacitor 3, but since the first and second diodes 4 and 5 are connected, the current on the low voltage side of the resonance capacitor 3 is reduced. The potential is the second diode 5
Rises to the potential of the primary winding tap-down to which the cathode is connected, and resonates along the route from the resonance capacitor 3 to the primary coil 7.

With the generation of the resonance pulse, the potential of the tap-down portion of the primary coil 7 decreases as shown in FIG. After the peak point of the pulse voltage, the resonance current flows through the route from the resonance capacitor 3 to the first diode 4.

On the other hand, as described above, the peak voltage at the tap portion is set substantially equal to the power supply voltage, so that the potential on the anode side of the second diode 5 at the time when the pulse reaches the peak is substantially zero potential. It has become. For this reason, the voltage at the pulse peak is substantially symmetrical.

When the pulse voltage becomes equal to or lower than the ground potential, a damper period starts, the damper diode 2 turns on, and the primary coil 7 is turned on from the damper diode 2 side.
Current flows to the side.

When the damper diode 2 is turned off at the end of the damper period, the current flowing through the primary coil 7 attempts to flow through the resonance capacitor 3, but the cathode side of the second diode 5 is almost at the power supply voltage. Therefore, resonance does not occur, and unnecessary resonance pulses are not generated during this period.

[0034]

As described above, according to the present invention,
With a simple configuration in which the diode of the diode clamp circuit connected to the resonance capacitor is connected to the tap-down winding provided in the flyback transformer, it is possible to improve the drawback of the conventional example in which the pulse voltage becomes left-right asymmetric.

In addition, it becomes possible to use a switching element having a low withstand voltage and to provide a power supply circuit having a higher voltage stability.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic configuration of a power supply device of the present invention.

FIG. 2 is a circuit diagram of a power supply device according to the embodiment of the present invention.

FIG. 3 is a pulse waveform diagram at each part of the power supply circuit shown in FIG. 2;

FIG. 4 is a circuit diagram of a power supply device according to a conventional example.

FIG. 5 is a pulse waveform diagram in each section of the power supply circuit shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching element 2 Damper diode 3 Resonant capacitor 4 First diode 5 Second diode 6 Drive power supply 7 Primary coil 8 Flyback transformer 10 FET as a switching element 11 Resistance 12 PWM

Claims (1)

[Claims] 1. A drive power supply is connected to one end of a primary coil of a flyback transformer, and the other end of the primary coil of the flyback transformer controls on / off of a current flowing through the primary coil, and a high voltage output fluctuation generated. A switching element whose ON period is controlled in response to the switching element, a resonance capacitor that resonates with the primary coil when the switch is turned off, and a damper diode that flows a damper current during the damper period are connected. A first diode is connected with the anode as an anode, between a connection end of the resonance capacitor and the first diode and a position tapped down by a resonance pulse voltage substantially corresponding to a driving power supply winding power supply voltage of a primary coil. And a second diode connected to the connection end side as an anode. Source circuit.