JPH04302583A - High voltage protecting circuit - Google Patents

Abstract

PURPOSE:To detect and act abnormality in a hot circuit without using an insulating element such as a photocoupler to be used for feeding back the hot circuit to a cool circuit in a high voltage protecting circuit for previously preventing the generation of a damages or the like in the circuits and apparatuses at the time of generating the abnormality in a high voltage generating circuit or the like in a CRT display device. CONSTITUTION:A horizontal driving circuit provided with a horizontal driving transformer T2 connecting one end of the primary side to the collector of a horizontal driving transistor(TR) TR1, receiving power supply to the other end of the primary side through a resistor and supplying a secondary side output to the base of a horizontal output TR TR2 is constituted of an SCR 3 connecting its anode to the other end of the primary side of the transformer T2 and grounding its cathode, and an overcurrent detecting circuit 2 receiving power supply from an input terminal 4, supplying power from an output terminal 5 to a flyback transformer and connecting an overcurrent detecting signal output terminal 6 to the gate of the SCR 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage protection circuit for preventing damage to circuits and equipment when an abnormality occurs in the high voltage generating circuit of a cathode ray tube display device.

0002

2. Description of the Related Art FIG. 3 is a block diagram of essential parts of an embodiment of a conventional high voltage protection circuit. In the figure, 31 is a horizontal oscillation circuit, T1 is an isolation transformer, TR1 is a horizontal drive transistor, T2 is a drive transformer, TR2 is a horizontal output transistor, D1 is a damper diode, DY is a deflection yoke, and T3 is a flyback transformer (FBT). ,
D2 is a high-voltage rectifier diode, D3 is a rectifier diode for obtaining the DC voltage V1, R1 and R2 are resistors, C1 to C4 are capacitors, 32 is a DC power line that supplies DC power to the horizontal drive circuit and the horizontal output circuit, 33
monitors the current (IL) flowing into the horizontal output circuit from the DC power supply line, and detects an overflow when the current (IL) exceeds the normal value due to an abnormality in the horizontal output circuit or T3 (flyback transformer), etc. An overcurrent detection circuit 34 outputs a current detection signal, and an overcurrent detection circuit 34 connects the overcurrent detection signal to a diode D41.
This is a photocoupler that feeds back to the horizontal oscillation circuit 31 via the transistor TR31. In monitor devices or color television receivers that are provided with terminals for connection to external devices, it is necessary to insulate the connection terminals from input alternating current power (AC) to prevent electric shock to the human body. As a means for this, there is a method of providing an insulating transformer in the power supply circuit, and there is also a method shown in FIG. FIG. 3 shows a method of insulating with T1 and T3. 1 of T3 from the secondary side (N2) of T1
The range on the next side (N1) is a so-called live part (a part that receives an electric shock), and the rest is a non-live part (a part that does not receive an electric shock). The live part is called a hot circuit, and the non-live part is called a cool circuit. The ground is also separate as shown. In addition, since the power supply line 32 in the case of FIG. 3 is the hot circuit, a voltage V1 obtained by rectifying the winding N3 of T3 is used as a DC power source for the cool circuit. The high voltage protection circuit in FIG. 3 transfers the overcurrent detection signal to the photocoupler 34.
This is a method of transmitting the signal to TR31 (collector-emitter) of the horizontal oscillation circuit and stopping the oscillation operation of the horizontal oscillation circuit. When oscillation stops, the horizontal output circuit also stops operating, so high voltage generation also stops, protecting the circuit and equipment from abnormal conditions. Once oscillation is stopped in such a situation, that state is held. The reason why an insulating element such as the photocoupler 34 is used is that the overcurrent detection circuit 33 belongs to a hot circuit and the horizontal oscillation circuit belongs to a cool circuit, so it is impossible to directly connect the two. Incidentally, such an insulating element is required to have specified dielectric strength performance from the viewpoint of preventing electric shock.

0003

Since the high voltage protection circuit shown in FIG. 3 constitutes a feedback loop from the hot circuit to the cool circuit, an insulating element such as the photocoupler 34 having the dielectric strength performance is essential. An object of the present invention is to provide a high-voltage protection circuit that can detect abnormalities in the hot circuit and take measures therefor without using such an insulating element.

0004

[Means for Solving the Problems] In the present invention, one end of the primary side is connected to the collector of a horizontal drive transistor, power is supplied to the other end of the primary side via a resistor, and the output of the secondary side is connected to the collector of a horizontal drive transistor. In a horizontal drive circuit provided with a horizontal drive transformer that is supplied to the base of a horizontal output transistor, an SCR whose anode is connected to the other end of the primary side of the horizontal drive transformer and whose cathode is grounded, and a The present invention provides a high voltage protection circuit comprising an overcurrent detection circuit to which the power is supplied, the flyback transformer is supplied with power from the output terminal, and the overcurrent detection signal output terminal is connected to the gate of the SCR. Alternatively, in the horizontal drive circuit, there is provided a high voltage protection circuit comprising an SCR whose anode is connected to the collector of the horizontal drive transistor, whose cathode is grounded, and whose gate is connected to the overcurrent detection signal output terminal. be.

[0005]

[Operation] Monitors the current flowing into the horizontal output circuit (including flyback transformer) from the power supply, and if the inflow current exceeds the normal value due to an abnormality in the circuit, an overcurrent detection signal is generated and the current flows into the horizontal output circuit (including flyback transformer). SCR (SILI) is activated by overcurrent detection signal.
CON CONTROLLED RECTIFFIRE)
By making the horizontal drive circuit conductive and cutting off the power supply to the horizontal drive circuit, the operation of the horizontal drive circuit and subsequent circuits is stopped.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A high voltage protection circuit according to the present invention will be explained below with reference to the drawings. FIG. 1 is a circuit diagram of a main part showing one embodiment of a high voltage protection circuit according to the present invention, and FIG. 2 is a circuit diagram of a main part showing another embodiment. 1 and 2, the same parts as in FIG. 3 are given the same symbols, 1 is a horizontal oscillation circuit, 2 is an overcurrent detection circuit, 3 is an SCR, TR3 is a transistor, R3 to R7 are resistors, and C5 and C6 is a capacitor.

Next, the operation of FIG. 1 will be explained. Current flowing into the horizontal output circuit from the DC power supply line 32 (
IL) An overcurrent detection circuit 2 is provided in the middle of the path. In the overcurrent detection circuit 2, current IL flows through R3, so R
3, a voltage drop proportional to the current IL occurs. This voltage is averaged by the integral action of R4 and C5 and is divided by R4 and R5 to provide a bias voltage V2 between the base and emitter of TR3. R3 to R5 and C5 are set so that when the current IL is below a normal value, TR3 is in an off state (collector current is zero), and when it exceeds a normal value, it is in an on state (collector current flows). Therefore, when the current IL exceeds a normal value, a voltage V3 is generated across R6 due to the collector current. The voltage V
3 is applied to the gate of SCR3, so SCR3
Make the anode and cathode conductive. As shown in the figure, since the anode is connected to the power line and the cathode is grounded, the power to TR1 is cut off and the horizontal drive operation is stopped. When the horizontal drive operation stops, the horizontal output also stops, and high voltage generation also stops. Incidentally, C6 and R7 are provided to set the gate voltage of the SCR3 to an appropriate value free of ripple components. Figure 2 shows S in Figure 1.
This is a method in which the anode of CR3 is directly connected to the collector of TR1, and the collector is directly grounded through conduction between the anode and cathode, thereby stopping the horizontal drive operation. The SCR3
The process of reaching the on state (conducting state between the anode and cathode) is the same as that shown in FIG. In both the embodiments of FIGS. 1 and 2, the on state of the SCR 3 is held as long as the voltage of the power supply line 32 is present. When the power to the device is turned off and the voltage on the power line 32 disappears, the on state is canceled, but as long as there is an abnormality in the horizontal output circuit, the SCR 3 is turned on again in the above process.

[0008]

As explained above, according to the present invention, it is possible to detect the high voltage protection of the cathode ray tube display device, which consists of the hot circuit and the cool circuit, in the hot circuit and take protective measures. Since it covers both the circuit and the cool circuit, it has the effect of eliminating the need for an insulating element compared to the conventional method of using an insulating element having a specified withstand voltage performance, and greatly contributes to improving the reliability of the high voltage protection circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a main part of an embodiment of a high voltage protection circuit according to the present invention.

FIG. 2 is a circuit diagram of main parts showing another embodiment of the high voltage protection circuit according to the present invention.

FIG. 3 is a block diagram of main parts showing an example of a conventional high voltage protection circuit.

[Explanation of symbols]

1 Horizontal oscillation circuit 2 Overcurrent detection circuit 3 SCR 4 Input terminal 5 Output terminal 6 Overcurrent detection signal output terminal 31 Horizontal oscillation circuit 32 DC power supply line 33 Overcurrent detection circuit 34 Photocoupler TR1 Horizontal drive transistor TR2 Horizontal output transistor TR3 Transistor R1 Resistor R2 Resistor R3 Resistor R4 Resistor R5 Resistor R6 Resistor C1 Capacitor C2 Capacitor C3 Capacitor C4 Capacitor C5 Capacitor C6 Capacitor T1 Insulating transformer T2 Drive transformer T3 Flyback transformer (FBT) D1 Damper diode D2 High voltage rectifier diode D3 Diode DY Deflection yoke

Claims (2)

[Claims] Claim 1: One end of the primary side is connected to the collector of a horizontal drive transistor, power is supplied to the other end of the primary side via a resistor, and a secondary side output is supplied to the base of the horizontal output transistor. In a horizontal drive circuit including a horizontal drive transformer, the anode is connected to the other end of the primary side of the horizontal drive transformer, the cathode is grounded, and the power is supplied from the input end, and the output end 1. A high-voltage protection circuit comprising: an overcurrent detection circuit that supplies power to a flyback transformer, and has an overcurrent detection signal output terminal connected to the gate of the SCR. 2. The horizontal drive circuit comprises an SCR having an anode connected to the collector of the horizontal drive transistor, a cathode grounded, and a gate connected to the overcurrent detection signal output terminal. High voltage protection circuit.