JPH0638631B2 - High voltage circuit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a high-voltage circuit such as a television, and more particularly to a high-voltage circuit capable of stably outputting a large output.

[Background of the Invention]

In recent years, a large-sized projection display using a cathode ray tube has been developed, and it is necessary to supply a large amount of power to the projection tube in order to increase its brightness. Conventionally, as a high voltage circuit for this purpose, since a plurality of flyback transformers are used, it is known that a plurality of high voltage circuits are provided and a circuit that balances output currents of the plurality of high voltage circuits is provided. For example, JP-A-56-149178 and JP-A-59-10.
3472 publication. However, since the same number of high-voltage circuits as flyback transformers are required, the circuit scale becomes large, and the conventional control circuit that balances the output current includes a high-voltage output circuit that is a time constant circuit in its loop. There was a problem that the control response speed was slow.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to drive a plurality of flyback transformers with one high-voltage output circuit.
Another object of the present invention is to provide a high voltage circuit capable of balancing output currents of a plurality of flyback transformers at high speed.

[Outline of Invention]

In order to achieve the above object, in the high voltage circuit according to the present invention, the primary side of a plurality of flyback transformers is connected to one high voltage output circuit, and the booster ratio of the booster ratio is added to the secondary side low voltage side terminal of the flyback transformer. An addition voltage source for correcting variations is provided, and the output currents of a plurality of flyback transformers are balanced at high speed by controlling the addition voltage source.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. First
In the figure, 1 is a switching pulse input terminal, 2 is a high voltage output switching transistor, 3 is a damper diode, 4 is a resonance capacitor, 5a and 5b are flyback transformers, 6a and 6b are high voltage rectification diodes, and 7a,
7b is a high voltage output terminal, 8a, 8b, 9a and 9b are resistors, 10a and 10b are addition voltage source control circuits, 11a and 11b are addition voltage sources, 12a and 12b are capacitors, 13 is a reference voltage source, and 14 is a power supply. It is an input terminal.

Next, the operation will be described with reference to the drawings.

When a switching pulse (usually a horizontal synchronizing pulse) is input to the switching pulse input terminal 1, the switching transistor 2 performs a switching operation, and a pulse current flows through the primary side of the flyback transformers 5a and 5b, and the secondary side of each of them. A high voltage is induced at. Rectifier diode 6
This high voltage is rectified by a and 6b, and the high voltage output terminal 7
A high DC voltage is output to a and 7b. High voltage output terminal 7a
The DC high voltage output to is divided by the resistors 8a and 9a and added as one input of the added voltage source control circuit 10a. The reference voltage from the reference voltage source 13 is applied to the other input of the added voltage source control circuit 10a, and the added voltage source control circuit 10a controls the added voltage source 11a so that the two inputs become equal to each other. The high DC voltage output from the output terminal 7a is stabilized to a constant level. Further, the DC high voltage output from the high voltage output terminal 7b is also applied to the resistors 8b and 9
b, the addition voltage source control circuit 10b, and the addition voltage source 11b similarly stabilize. Also, two added voltage source control circuits
Since the same reference voltage is used for 10a and 10b, the DC high voltage output from the high voltage output terminals 7a and 7b has the same value. This circuit is mainly suitable for a multi-tube projection display, for example, in the case of 6-tube projection,
RG, B 7a is connected to one set of projection tubes, and 7b is connected to another set of projection tubes.

The circuit of FIG. 1 shows the case where two flyback transformers are used, but it is clear that the same configuration can be achieved when three or more flyback transformers are used.

FIG. 2 is a circuit diagram showing in detail the main part of FIG. 7, and shows only one of the two high voltage control circuits shown in FIG. In FIG. 2, the added voltage source 11 is a control transistor.
27, 28, an overload detection transistor 29, an operational amplifier 39, a photocoupler 40 and the like. A DC voltage of about 1200 V, which is obtained by rectifying the tertiary winding voltage of the flyback transformer 5 by the diode 18 and smoothed by the capacitor 22, is applied to the power input terminal 23 for the added voltage source. In addition, the floating power supply input terminals 24 and 25 rectify the tertiary winding voltage of the flyback transformer 5 with diodes 16 and 17, and
DC voltage smoothed at 0 and 21 is applied. Since the addition power supply output terminal 26 is connected to the low-voltage side terminal of the secondary winding of the flyback transformer 5, the high-voltage output voltage of the high-voltage output terminal 7 is high.
E _HV is expressed by equation (1).

E _HV = E ₂ + V ₀ (1) However, E ₂ is a DC voltage obtained by rectifying the secondary winding voltage with the diode 6, and V ₀ is the output voltage of the addition voltage source 11. On the low voltage side of the secondary winding of the flyback transformer 5, a capacitor 19 and an added voltage source for realizing a low impedance in AC.
A diode 15 is provided as a protection circuit when 11 is a failure.

The output voltage V ₀ of the added voltage source 11 is expressed by the equation (2).

However, R ₃₆ is the resistance value of the resistor 36, R ₃₇ is the resistance value of the resistor 37, and V ₃₅ is the voltage across the resistor 35.

V ₃₅ can be changed by the current flowing through the light emitting diode which is the primary side of the photocoupler 40, and this light emitting diode is connected to the addition voltage source control circuit 10.

The control transistors 27, 28 are in a totem pole connection, and the resistors 30, 31, 33 and the diode 38 are provided to balance the collector-emitter voltage V _CE of these two control transistors. When an abnormally high voltage output current flows due to high voltage discharge, etc., the abnormal current is detected by the resistor 32 to make the transistor 29 conductive, and the control transistor
27 and 28 are cut off to protect the transistor from damage.

The added voltage source control circuit 10 is a differential transistor for error amplification.
44, 46 and a resistor 45, the output voltage of a variable resistor 48 provided at the emitter of the high-voltage detection transistor 47 of the emitter follower and the output voltage of the reference voltage source 13 including the resistor 42 and the Zener diode 43 become equal. Like, photo coupler
The added voltage source 11 is controlled via 40 to stabilize the high voltage.

FIG. 3 shows the regulation characteristic of this high-voltage circuit. A curve 49 shows the regulation characteristic of the conventional high voltage circuit, a curve 49 'shows the regulation characteristic of the high voltage circuit of the present invention, and a curve 50 shows the output voltage characteristic of the addition voltage source in the high voltage circuit of the present invention.

FIG. 4 is a circuit diagram showing in detail a modification of the first embodiment of the high voltage circuit according to the present invention. In FIG. 2, the addition voltage source 11 is configured by a series regulator, whereas in FIG. 4, it is configured by a switching regulator.

The operation of FIG. 4 will be described.

The added voltage source 11 includes a switching transistor 53, a high frequency transformer 55, a rectifying diode 56, and the like. When a switching pulse is input to the switching pulse input terminal 52, the switching transistor 53 performs a switching operation and a high voltage is induced on the secondary side of the high frequency transformer 55.
This high voltage is rectified by the rectifying diode 56, and the added voltage source output voltage is applied from the added voltage source output terminal 26 to the secondary side low voltage side terminal of the flyback transformer 5 as in the case of FIG. Since the output voltage of the addition voltage source 11 is proportional to the power supply voltage applied to the power supply input terminal 23 for the addition voltage source, the addition voltage source control circuit 10 changes the power supply voltage applied to the terminal 23 in the circuit of FIG. It is a control circuit. The addition power supply control circuit 10 is composed of error amplification differential transistors 44 and 46, a power supply control transistor 67, and the like, and the output voltage of the variable resistor 48 provided at the emitter of the high-voltage detection transistor 47 of the emitter follower and the resistor 42, The added voltage source 11 is controlled to stabilize the high voltage so that the output voltages of the reference voltage source 13 including the Zener diode 43 become equal. The control transistor 67 uses a common emitter type whose collector voltage control range is wide. Further, the frequency of the switching pulse that drives the added voltage source and the frequency of the switching pulse that drives the high voltage output circuit do not have to be the same.

FIG. 5 is a block diagram showing a second embodiment of the present invention. In FIG. 5, 7 is a high-voltage output terminal, 8, 9, 57a,
57b, 59, 60, 61, 62 are resistors, and 58 is an operational amplifier.

FIG. 5 shows a point in which the number of high voltage output terminals is one and a circuit for detecting the output currents of the two flyback transformers 5a and 5b and adding a circuit for balancing the output currents of the two flyback transformers 5a and 5b. It is different from Fig. 1 in that it was done.

Next, the operation will be described with reference to the drawings.

Fig. 5 is suitable when a high-output high-voltage circuit is required for the direct-view type or single-tube projection type. In this application, since the outputs of each flyback transformer are connected in parallel at the high-voltage output terminals, the output of each flyback transformer is shown. A circuit to balance the current is needed.

Conventionally, the circuit that balances the output current of this flyback transformer was a circuit that controls the power supply voltage of the high-voltage output circuits provided in the same number as the flyback transformer, so the high-voltage output circuit becomes a time constant circuit and its response speed is It wasn't enough. In this embodiment, added voltage sources 11a and 11b provided on the low voltage side of the two flyback transformers 5a and 5b.
The current detection resistors 57a and 57b that detect the high-voltage output current of each flyback transformer are provided between the low-voltage side terminal and the ground,
The terminal voltage of the resistor is input to the operational amplifier 58, and the output voltage of the operational amplifier 58 is input to the addition power supply control circuit 10a so that the high voltage output currents of the flyback transformers are equalized.

Therefore, the high-voltage output circuit, which is a time constant circuit, is not included in the control loop, so that the response speed of control is high.

FIG. 6 shows a detailed circuit diagram for implementing the block diagram of FIG. As the addition voltage sources 11a and 11b, the same series regulator as in FIG. 2 is used, and the addition voltage source control circuit is used.
10a and 10b also use the same differential amplifier as in FIG. The detection of the high voltage output current of each flyback transformer is performed by providing resistors 57a and 57b on the low voltage side of the tertiary winding of the flyback transformer that obtains the added voltage source current.

Capacitors 63a and 63b are provided to drop the low-voltage side terminal of the tertiary winding AC to ground. Other operations of this circuit are similar to those described with reference to FIG.

〔The invention's effect〕

As described above, according to the present invention, the primary side of a plurality of flyback transformers is connected to one high voltage output circuit, and the booster ratio of the booster ratio is applied to the secondary side low voltage side terminals of these flyback transformers. Since the addition voltage source that corrects the variation is provided, a plurality of flyback transformers can be driven by one high-voltage output circuit, and an economical large-output high-voltage circuit can be realized. Further, by controlling the addition voltage source provided on the secondary side of the flyback transformer, it is possible to quickly correct the variations in the output currents of the plurality of flyback transformers, so that the stability of the high voltage circuit can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a high voltage circuit of the present invention, FIG. 2 is a first detailed circuit diagram for realizing the block diagram of FIG. 1, and FIG. 3 is a circuit operation of FIG. FIG. 4 is a characteristic diagram for explaining, FIG. 4 is a second detailed circuit diagram for realizing the block diagram of FIG. 1, and FIG. 5 is a block diagram showing a second embodiment of the high voltage circuit of the present invention. The figure is a detailed circuit diagram for implementing the block diagram of FIG. 1 ... Switching pulse input terminal 2 ... Switching transistor 3 ... Damper diode 4 ... Resonance capacitor 5, 5a, 5b ... Flyback transformer 6, 6a, 6b ... High voltage rectification diode 7, 7a, 7b ... High voltage Output terminals 8, 8a, 8b, 9, 9a, 9b ...... Resistors 10, 10a, 10b ...... Addition voltage source control circuit 11, 11a, 11b ...... Addition voltage source 12, 12a, 12b ...... Capacitor 13 ...... Reference voltage source 14 …… Power input terminal 15,15a, 15b, 16,16a, 16b, 17,17a, 17b, 18,18a, 18b …… Diode 19,19a, 19b, 20,20a, 20b, 21,21a , 21b, 22,22a, 22b …… Capacitor 23,23a, 23b …… Supply voltage source power input terminal 24,24a, 24b, 25,25a, 25b …… Floating power input terminal 26,26a, 26b …… Addition Voltage source output terminal 27,28 …… Control transistor 29 …… Overload detection transistor 30,31,32,33,34,35,36,37 …… Resistor 38 …… Diode, 39 …… Comparison amplification 40,40a, 40b …… Photocoupler 41 …… Capacitor 42,45,45a, 45b …… Resistor 43 …… Zener diode 44,44a, 44b, 46,46a, 46b …… Differential transistor 47 for error amplification… … Detecting transistor 48 …… Variable resistor 49,49 ′ …… High voltage regulation characteristics 50 …… Addition voltage source output voltage characteristics 51 …… Power input terminal 52 …… Switching pulse input terminal 53 …… Switching transistor 54 …… Capacitor , 55 …… High frequency transformer 56 …… Rectifier diode 57a, 57b …… Current detection resistor 58 …… Operational amplifier 59, 60, 61, 62, 66 …… Resistor 63a, 63b …… Capacitor 64, 65 …… Power supply Input terminal 67 …… Power control transistor

Claims (2)

[Claims] 1. A high voltage circuit comprising a high voltage output transistor, a damper diode, a resonance capacitor, and a flyback transformer, wherein a plurality of flyback transformers are provided and connected to the primary side of the plurality of flyback transformers.
Individual high voltage output transistors, summing voltage sources connected to the secondary side low voltage side terminals of the plurality of flyback transformers, and further connected to the plurality of flyback transformers, respectively. A detection circuit for detecting a voltage is compared with an output voltage of the detection circuit and a preset reference voltage, and a control circuit for controlling the plurality of added voltage sources is provided so that an error between them is reduced. A high-voltage circuit characterized in that 2. The output terminals of the plurality of flyback transformers are connected in parallel, and an output current detection circuit for detecting the output current of each of the plurality of addition voltage sources is provided, and the output voltage of each of the output current detection circuits. The high-voltage circuit according to claim 1, further comprising a control circuit that controls the plurality of added voltage sources so that the two are equal to each other.