JPH0681262B2 - High voltage generation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high voltage generating circuit provided with a means for preventing a rare short circuit occurring in a high voltage coil of a flyback transformer.

[Conventional technology]

The high voltage generation circuit of a television receiver or a CRT display device includes a flyback transformer that boosts a flyback pulse. This flyback transformer is usually subjected to a high voltage of about 30 Kv, and a rare short circuit occurs in the high-voltage coil of the flyback transformer due to a manufacturing error, for example, and when this progresses, the flyback transformer emits smoke.・ It will ignite, leading to a major accident such as a fire.

The high-voltage coil is sufficiently quality-controlled so that such a rare short circuit does not occur, but it is expected that a fine defective portion will be overlooked and it will be used as a good product. When used, as described above,
This will cause a major accident such as a fire.

In recent years, in order to prevent an accident such as a fire caused by such a rare short, a rare short detection circuit is provided, and when a rare short is detected by this circuit, the circuit operation is immediately stopped. It has been devised.

FIG. 3 shows a circuit incorporated in a conventional high voltage generating circuit for detecting a rare short circuit and performing a protection operation. When a rare short circuit occurs in the high voltage coil of the flyback transformer, this circuit detects the primary side current that increases due to the rare short circuit and stops the horizontal oscillation circuit (not shown). That is, when the rare short circuit does not occur normally, the primary current of the flyback transformer is approximately 1 A or less. At this time, the voltage drop of the resistor 1 in the circuit of FIG.
Remains off. On the other hand, when a rare short circuit occurs and an abnormal state occurs, the primary side current increases to about 2 A, and the voltage drop across the resistor 1 increases accordingly, turning on the transistor 2. As a result, the voltage of the capacitor 3 rises, the Zener diode 4 turns on, and the transistor 5 also turns on at the same time. This allows
The light emitting diode inside the photocoupler 6 is driven, the transistor 7 in the non-charging part is turned on, and the capacitor 8
The electric charge stored in the capacitor 9 is charged in the capacitor 9, drives the X-ray protection terminal 11 of the photocoupler 10, and stops the oscillation of the horizontal oscillation circuit. The stop of the horizontal oscillation circuit also stops the operation of the flyback transformer, thereby preventing the occurrence of a fire or the like due to a rare short circuit.

[Problems to be Solved by the Invention]

However, in the conventional circuit of this type, as shown in FIG. 3, the number of circuit components used is large and the circuit is complicated, so that the circuit is complicated to manufacture. There is a problem that the cost becomes high.

Although the circuit shown in FIG. 3 certainly stops the horizontal oscillation circuit when a rare short circuit occurs in the high voltage coil, it does not have a latch function for stopping the circuit, and the horizontal oscillation circuit is erroneously detected. When the circuit is turned on again, there is a danger that the flyback transformer will operate and the rare short circuit will progress further.

The present invention has been made to solve the above-described conventional problems, and an object thereof is to be able to detect an abnormality of a rare short circuit with a simple circuit configuration, and when a rare short circuit is once detected. It is an object of the present invention to provide a high-voltage circuit capable of holding a flyback transformer having a latch function and keeping the circuit operation stopped.

[Means for Solving the Problems]

The present invention is configured as follows to achieve the above object. That is, the present invention comprises a horizontal deflection output circuit that generates and outputs a flyback pulse, and a flyback transformer that boosts the flyback pulse generated by this horizontal deflection output circuit and applies the boosted output to the cathode of the cathode ray tube. In the high voltage generating circuit, a protective fuse connected to the low voltage end side of the low voltage coil forming the flyback transformer, a primary side current detection circuit for detecting the primary side current flowing through the low voltage coil, and the primary side current detection circuit When the current capacity detected by exceeds the reference value, the gate is opened to open a gate to flow a fusing current to the protective fuse to blow the protective fuse, and a steep noise fluctuation voltage applied to the gate circuit is removed. A voltage smoothing circuit for preventing malfunction of the gate circuit, wherein the low-voltage coil, the gate circuit, and the protective fuse are Is connected to the column is configured as characterized by forming a closed loop.

[Action]

In the present invention configured as described above, when a rare short circuit occurs in the high voltage coil forming the flyback transformer, the primary side current flowing through the low voltage coil sharply increases. The increase amount of the primary side current is detected by the primary side current detection circuit, and when the detected current capacity exceeds the reference value, the gate of the gate circuit is opened, and the fusing current is applied to the protection fuse. The fusing current blows the protective fuse, and the operation of the flyback transformer stops accordingly.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of a high voltage generating circuit showing an embodiment of the present invention. In the figure, the high voltage generation circuit includes a horizontal deflection output circuit 12, a high voltage circuit 13, and a rare short circuit detection / detection circuit.
And a protection circuit 14. Of these, rare short detection
Since the circuits other than the protection circuit 14 are known, the description of those known circuits will be simplified.

The horizontal deflection output circuit 12 includes a horizontal output transistor 19
, A damper diode 15, a resonance capacitor 16, a horizontal deflection coil 17, and an S-shaped correction capacitor 18.
The horizontal output transistor 14 receives a voltage pulse sent from a horizontal drive circuit (not shown) and performs a switching action, and in cooperation with the damper diode 15, applies a sawtooth current to the horizontal deflection coil 17. On the other hand, the resonance capacitor 16 and the horizontal deflection coil 17 generate a flyback pulse by its resonance action and apply it to the high voltage circuit 13.

The high voltage circuit 13 includes a flyback transformer 20 and a high voltage rectifier diode 21. The high-voltage side terminal 23 of the low-voltage coil (primary coil) 22 of the flyback transformer 20 is connected to the common terminal of the horizontal deflection coil 17 and the resonance capacitor 16, and the low-voltage side terminal 24 of the low-voltage coil 22 and the intermediate tap.
A rare short detection / protection circuit 14 is connected between the line 25 and the line 25.

On the other hand, the high voltage side terminal of the high voltage coil (secondary coil) 26 of the flyback transformer 20 is connected to the anode 28 of the cathode ray tube 27 via the high voltage rectifying diode 21. In the circuit of this embodiment, one end of the circuit of the focus pack 30 is connected to the cathode side of the high voltage rectifier diode 21. The circuit of this focus pack 30 is composed of a resistor 31, a variable resistor VR _F for adjusting the focus output, and a variable resistor VR _S for adjusting the screen voltage.
The end of the series connection body of 1, VR _F and VR _S on the side of the resistor 31 is connected to the cathode side of the high-voltage rectifying diode 21, and the end on the side of the variable resistor VR _S is connected to the ground side. . Also,
The low voltage side of the high voltage coil 26 is ABL (Automatic Brightness Li
miter). In such a configuration, the high voltage circuit 1
Reference numeral 3 indicates that the flyback pulse applied from the horizontal deflection output circuit 12 is boosted by the flyback transformer 20 and signal rectification is performed by the high voltage rectification diode 21, and the rectified output is applied to the anode 28.

The rare short detection / protection circuit 14 reliably detects a rare short generated in the high voltage coil 26 of the flyback transformer 20 and performs a safe operation thereof, and is a characteristic circuit of this embodiment. This rare short detection / protection circuit 14
Includes a protective fuse 32, a detection resistor 33 as a primary side current detection circuit, a thyristor 34 as a gate circuit, and a smoothing capacitor 35 as a voltage smoothing circuit.

One end of the protective fuse 32 is connected to the low voltage side terminal 24 of the low voltage coil 22, and the other end of the fuse 32 is connected in series with a detection resistor 33. And this detection resistor 33
The other end side of is connected to the positive side of the input power supply 36. The negative side of the input power source 36 is connected to the ground. The input power source 36 is provided with a power source fuse (not shown). The anode side of the thyristor 34 is connected to the intermediate tap 25 of the low voltage coil 22, and the cathode side of the thyristor 32 is connected to the connection portion between the protective fuse 32 and the detection resistor 33. The gate side of the thyristor 34 is connected to the common connection portion of the detection resistor 33 and the input power supply 36. A smoothing capacitor 35 is connected between the gate and cathode of the thyristor 34.

In the present embodiment configured as described above, during the circuit operation, the primary side current I _B flowing through the low voltage coil 22.
Is converted into a voltage value by the detection resistor 33 and detected.

That is, this detection voltage e _B changes the resistance value of the detection resistor 33.
If R ₁ , then e _B = I _B × R ₁ , and this detection voltage e _B is
As a result, a steep voltage fluctuation component such as a sawtooth component or noise is removed and added to the cathode of the thyristor 34 as a voltage ec.

On the other hand, a voltage eq is applied to the gate side of the thyristor 34, and assuming that the gate-cathode voltage at which the thyristor 34 is turned on is V _G , during normal operation where there is no rare short circuit in the high voltage coil 26, eq <ec + v _G , and the gate of the thyristor 34 remains closed.

In contrast, when the short circuit occurs in the high-pressure coil 26, it increases the primary current I _B.

That is, when a rare short circuit occurs in the voltage coil 26, energy consumption increases at the short circuit portion. Now, assuming that the short energy consumed per one turn of the rare short is q, when the rare short is expanded to n turns, the energy P consumed from that portion becomes P = nq.

In this case, since this short-circuit energy P is supplied from the input power source 36, when a rare short-circuit occurs, the primary side current I _B
Increases by ΔI _B. That is, when the primary side of the current during normal no short circuit and I _BO, current I _B of the primary side at the time of short circuit is expressed as follows.

I _B = I _BO + ΔI _B Therefore, ΔI _B = P / E _B = nq / E _B. However, E _B is the power supply voltage of the input power supply 36.

As described above, when a short circuit occurs in the high voltage coil 26, the primary side current increases by ΔI _B , and the primary side current capacity, that is, the detection voltage e _B detected by the detection resistor 33 increases accordingly. Then, as a result of the voltage ec applied to the cathode of the thyristor 34 decreasing, eq> ec + v _G , and the thyristor 34 operates to open the gate. When the gate of the thyristor 34 is opened in this way, the high voltage side terminal of the low voltage coil 22 is
The voltage pulse generated between the intermediate tap 23 and the intermediate tap 25 is short-circuited, so that a large-capacity fusing current flows from the intermediate tap of the low-voltage coil 22 to the protective fuse 32 via the thyristor 34, and this protective fuse 32 melts. As a result, stop the supply of the primary-side current I _B supplied from the input power source 36 to the horizontal deflection output circuit 12, the operation of the flyback transformer 20 is stopped. This allows the high voltage coil
The energy supply to the 26 short-circuited portions is cut off, the heat generation at the short-circuited portions is stopped, and smoke and ignition from the flyback transformer 20 are prevented in advance.

As described above, according to the present embodiment, when a rare short circuit occurs in the high voltage coil 26, the protective fuse is blown, so that the circuit operation is latched in a stopped state. Therefore, unless the flyback transformer 20 is replaced with a normal one and the protective fuse 32 is replaced, the circuit will not operate again, and smoke / ignition accidents due to a rare short circuit can be prevented more safely.

Further, in the circuit shown in FIG. 1, the focus pack 30 is provided on the high voltage coil 26 side, and even if the circuit of this focus pack 30 causes a short circuit with a metal or the like in the vicinity thereof, the primary pack increased side current I _B, the gate is opened by the on operation of the thyristor 34, as well as the protection fuse 32 is blown. Therefore, in the circuit configuration of the present embodiment, not only a rare short circuit of the high voltage coil 26 but also a high voltage side abnormality such as a short circuit of the focus pack 30 is detected by the current increase of the primary side current, and the gate of the thyristor is immediately opened. Since the protection fuse is blown, safety due to a circuit abnormality on the high voltage side can be more effectively achieved.

The present invention is not limited to the above-mentioned embodiments and can take various modes. For example, in the above embodiment, the circuit configuration in which the high-voltage output circuit and the horizontal deflection output circuit are not separated has been shown, but when they are separated, the horizontal deflection coil 17 and the S-shaped correction capacitor 18 become unnecessary. However, also in this case, it is possible to change only the horizontal deflection coil 17 to a dummy inductance.

Further, in the above embodiment, the gate circuit is formed by the thyristor 34, but this gate circuit does not necessarily have to be formed by using the thyristor 34, and other appropriate circuit elements, for example, as shown in FIG. Alternatively, the transistor 37 may be used.

〔The invention's effect〕

As described above, the present invention uses the protective fuse connected to the low voltage coil side, the primary side current detection circuit, the gate circuit, and the voltage smoothing circuit to detect and protect a rare short circuit generated in the high voltage coil. Since the circuit is designed to achieve, the number of parts of the circuit element is small,
The circuit configuration is extremely simplified, and it is possible to facilitate the circuit manufacturing and reduce the device cost. Also,
Since the number of parts is small as described above, it is possible to increase the reliability of the circuit operation accordingly.

Further, in the present invention, when the rare short circuit is once detected, the protective fuse is blown, so that the circuit operation is latched in the stopped state, thereby further ensuring the safe operation against the rare short circuit. it can.

Furthermore, since the present invention is configured to detect an abnormality on the secondary side by increasing the current on the primary side, an abnormality other than a rare short circuit, such as a short circuit of the focus pack circuit connected to the high-voltage coil, can be detected, and the safety can be improved. You can take action.

Further, as described above, the circuit of the present invention for protecting the short circuit of the high voltage coil and its protection can be formed integrally with the flyback transformer, so that the circuit can be made compact and the handling thereof becomes easy. In addition, the circuit for detecting and protecting the rare short circuit can be configured only by the connection on the primary side of the flyback transformer, that is, the low-voltage coil side, which is convenient for achieving AC insulation of the circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a high voltage generating circuit according to the present invention, FIG. 2 is a circuit diagram showing one structural example of a gate circuit using a transistor, and FIG. 3 is incorporated in a conventional high voltage generating circuit. It is a circuit diagram of the detection protection circuit of the rare short circuit currently performed. 1 ... Resistor, 2 ... Transistor, 3 ... Capacitor, 4 ... Zener diode, 5 ... Transistor,
6 ... Photo coupler, 7 ... Transistor, 8,9 ... Capacitor, 10 ... Photo coupler, 11 ... X-ray protection terminal,
12 …… Horizontal deflection output circuit, 13 …… High voltage circuit, 14 …… Rare short detection / protection circuit, 15 …… Damper diode,
16 …… Resonance capacitor, 17 …… Horizontal deflection coil, 18 ……
S-shaped correction capacitor, 19 ... Horizontal output transistor, 20
...... Flyback transformer, 21 …… High voltage rectifier diode, 22 …… Low voltage coil, 23 …… High voltage side terminal, 24 …… Low voltage side terminal, 25 …… Middle tap, 26 …… High voltage coil, 27 ……
CRT, 28 ... Anode, 30 ... Focus pack, 31 ... Resistor, 32 ... Protective fuse, 33 ... Detecting resistor, 34 ... Thyristor, 35 ... Smoothing capacitor, 36 ...
… Input power, 37… transistor.

Claims (1)

[Claims] 1. A horizontal deflection output circuit for generating and outputting a flyback pulse, and a flyback transformer for boosting a flyback pulse generated by the horizontal deflection output circuit and applying the boosted output to an anode of a cathode ray tube. In the high voltage generation circuit, a protective fuse connected to the low voltage end side of the low voltage coil that constitutes the flyback transformer, a primary side current detection circuit that detects the primary side current flowing through the low voltage coil, and this primary side current detection circuit A gate circuit that opens a gate when a detected current capacity exceeds a reference value to flow a fusing current to the protection fuse to blow the protection fuse, and a gate that removes a sharp noise fluctuation voltage applied to the gate circuit. A voltage smoothing circuit for preventing malfunction of the circuit, and the low-voltage coil, the gate circuit, and the protection fuse are connected in series. High voltage generating circuit, characterized by being in form a closed loop is.