JPH0744645B2 - 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. 2 shows a circuit which is incorporated in a conventional high voltage generating circuit and which detects a rare short circuit and protects the short circuit. 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 photo cab 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. 2, the number of circuit components used is large and the circuit is complicated, which complicates the manufacturing of the circuit. There is a problem that the cost becomes high.

Further, the circuit shown in FIG. 2 certainly stops the horizontal oscillation circuit when a rare short circuit occurs in the high voltage coil, but does not have a latch function for stopping this circuit, so that the horizontal oscillation is erroneously made. 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 that has a latch function and can hold the stopped state of the circuit operation of the flyback transformer.

[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 transformer generated by this horizontal deflection output circuit and applies the boosted output to the anode of the cathode ray tube. In the high-voltage generating circuit, a protective fuse connected in series 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 DC current flowing through the low-voltage coil, and the primary-side A first gate circuit that opens a gate to output an operating current when the current capacity detected by the current detection circuit exceeds a reference value, and a gate opening time of the first gate circuit that receives the operating current. A second gate circuit which opens the gate when a preset time is exceeded and applies a fusing current to the protective fuse to blow the protective fuse. Cage, the primary-side current detection circuit and the first gate circuit and the second gate circuit are both configured as characterized by being formed on the low-voltage coil of the flyback transformer.

[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 DC current flowing through the low voltage coil sharply increases. This increase in the primary side DC current is detected by the primary side current detection circuit, and when the detected current capacity exceeds the reference value, the gate of the first gate circuit is opened and the operating current is transferred to the second gate circuit. Added. The second gate circuit detects the time when the first gate circuit opens the gate (ON operation time), opens the gate when the gate opening time exceeds a set time, and supplies a blowing current to the protective fuse. Add. 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 comprises a horizontal deflection output circuit 12, a high voltage circuit 13, and a rare short detection / protection circuit 14. Of these, the circuits other than the rare short detection / protection circuit 14 are known, and therefore the description of these 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 19 receives a voltage pulse sent from a horizontal drive circuit (not shown), performs a switching action, and in cooperation with the damper diode 15, applies a sawtooth wave 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 is described later. Rare short detection / protection circuit 14 is connected.

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 voltage, and a variable resistor VR _S for adjusting the screen voltage.
1, VR _F , VR _S and the end of the series connection body on the side of the resistor 31 are connected to the cathode side of the high-voltage rectifier 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
Is a detection resistor 33 as a primary side current detection circuit, a protection fuse 32, an input power supply 36, a PNP type transistor 34 as a first gate circuit, and a first voltage smoothing circuit.
Of smoothing capacitor 35, resistors 37 and 38, and a second gate circuit 40. The second gate circuit 40 comprises a thyristor 41, a second smoothing capacitor 42 as a voltage smoothing circuit, and a resistor 39.

One end of the detection resistor 33 is a low voltage side terminal of the low voltage coil 22.
The other end of the resistor 33 is connected to one end of the protective fuse 32. The other end of the protective fuse 32 is connected to the anode of the input power source 36. The cathode of the input power source 36 is connected to the ground. The input power supply 36 is provided with a power supply fuse. In the present embodiment, the protection fuse 32 also serves as this power supply fuse. The base side of the PNP transistor 34 is connected to the low voltage side terminal 24 of the low voltage coil 22 via a resistor 37. The emitter side of the PNP type transistor 34 is connected to the connection portion between the detection resistor 33 and the protective fuse 32. A first smoothing capacitor 35 is connected between the base and emitter of the PNP type transistor 34. The above
The collector side of the PNP transistor 34 is connected to the ground via a series connection body of resistors 38 and 39.

The anode side of the thyristor 41 forming the second gate circuit is connected to the emitter side of the PNP transistor 34, and the gate side of the thyristor 41 is connected to the connection portion between the resistors 38 and 39. In addition, the thyristor
The cathode side of 41 is connected to ground. A second smoothing capacitor 42 is connected between the gate and cathode of the thyristor 41.

In the present embodiment configured as described above, during the operation of the circuit, the primary side direct current I _B is flowing from the input power source 36 to the low voltage coil 22, and the primary side current I _B is It is converted into the voltage of I _B R ₁ by the detection resistor 33 and detected (R ₁ is the resistance value of the detection resistor 33). During normal operation without abnormalities such as rare short circuit in the high voltage coil 26, the voltage e ₁ (e ₁ = I _B R ₁ ) detected by the detection resistor 33 is lower than the ON operation voltage of the PNP type transistor 34. The type transistor 34 remains off, and the thyristor 41 also remains off.

On the other hand, when a rare short circuit occurs in the high voltage coil 26, the primary side DC current I _B increases.

That is, when a rare short circuit occurs in the high voltage coil 26, the 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 the short-circuit energy P is supplied from the input power source 36, when the rare short circuit occurs, the direct current I _B on the primary side increases by ΔI _B. That is, when a direct current of the primary side of the normal is not rare short and I _BO, DC current I _B of the primary side at the time of short circuit is expressed as follows.

I _B = I _BO + ΔI _B As described above, when a rare short circuit occurs in the high-voltage coil 26, the primary-side current I _B increases by ΔI _B , and along with this, the primary-side current capacity, that is, the detection resistor. The detection voltage e ₁ detected by 33 increases. When the detected voltage e ₁ exceeds the on-operation voltage of the PNP-type transistor 34, the PNP-type transistor 34 is turned on to open the gate, and an operation current is applied to the second gate circuit from the collector side. By adding this operating current, the gate of thyristor 41 has resistor 3
The drive voltage divided by the resistors 8 and 39 is applied, but in the present embodiment, the second smoothing capacitor 42 and the resistor 39 are connected in parallel between the gate and the cathode of the thyristor 41. Due to the time constant determined by the second smoothing capacitor 42 and the resistor 39, a certain time delay occurs until the voltage applied between the gate and cathode of the thyristor 41 exceeds the trigger voltage of the thyristor 41. When the PNP transistor 34 is turned off and the gate is closed during this time delay, the gate voltage of the thyristor 41 does not exceed the trigger voltage, so the gate of the thyristor 41 cannot be opened, but the time delay section due to the time constant is exceeded. Beyond the PNP transistor 34
When the ON operation continues, the voltage between the gate and the cathode of the thyristor 41 exceeds the trigger voltage after a time delay due to this time constant, and as a result, the thyristor 41 performs the ON operation and opens the gate. When the gate of the thyristor 41 is opened, the anode of the input power supply 36 and the ground are short-circuited, and a large current (fusing current) flows through the path a that sequentially goes from the input power supply 36 to the protective fuse 32, the thyristor 41, and the ground. The protective fuse 32 is blown by the electric current. As a result, the input power 36
Primary side DC current I _B supplied from the
Is stopped and the operation of the flyback transformer 20 is stopped. As a result, the energy supply to the rare short portion of the high voltage coil 26 is cut off, the heat generation at the short portion is stopped, and the smoke and fire from the flyback transformer 20 are prevented in advance.

In the circuit operation of the above embodiment, the first smoothing capacitor
35 removes noise components and steep voltage fluctuation components applied to the PNP type transistor 34 to prevent malfunction of the PNP type transistor 34, and the second smoothing capacitor 42 similarly eliminates noise components added to the thyristor 41 and The steep voltage fluctuation component is removed to prevent malfunction of the thyristor 41.

Further, in the present embodiment, the second smoothing capacitor 42 and the resistor 39
The time constant determined by
Since it takes a certain time for the voltage applied between the cathodes to exceed the trigger voltage of the thyristor 41, even if the PNP transistor 34 accidentally turns on due to a malfunction during this time, The gate-cathode voltage of the thyristor 41 does not exceed the trigger voltage, and the reliability of the operation of the thyristor 41 is significantly improved.

Further, in the circuit of FIG. 1, the focus pack 30 is provided on the side of the high voltage coil 26, but the case of the focus pack 30 has a hole or the like, and the insulation of the case is deteriorated. for example, the also increases the DC current I _B of the primary side when that caused the discharge and metal chassis or the like in the vicinity, the respective gate is opened by the on operation of the PNP transistor 34 and the thyristor 41,
Similarly, the protective fuse 32 is blown. Therefore, in the circuit configuration of the present embodiment, not only a short circuit of the high voltage coil 26 but also a high voltage side abnormality such as discharge from the focus pack 30 is detected by the increase in the primary side DC current, and the gate of the thyristor is opened immediately. Since the protective fuse is melted and blown, the safety due to the circuit abnormality on the high voltage side can be more effectively achieved.

In this embodiment, once the protective fuse 32 is blown, the circuit operation of the flyback transformer 20 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.

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.

In the above embodiment, the first gate circuit is composed of the PNP type transistor 34 and the second gate circuit is composed of the thyristor 41. However, this may be composed of other circuit elements. Good.

Further, although the first smoothing capacitor 35 is provided between the base and the emitter of the PNP type transistor 34 in the above embodiment, the first smoothing capacitor 35 can be omitted.

Further, in the above embodiment, the power fuse of the input power source 36 also serves as the protective fuse 32, but the protective fuse 32 may be provided separately from the power fuse.

〔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, and each of the first and second gate circuits as main circuit elements to generate a rare substance generated in the high-voltage coil. Since the circuit that detects and protects the short circuit is configured on the low-voltage coil side of the flyback transformer, the number of components of the circuit element is very small, which greatly simplifies the circuit configuration and facilitates circuit manufacturing. Both simplification and device cost reduction can be achieved. Further, 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, the gate of the second gate circuit is opened when a predetermined set time is exceeded after the first gate circuit is turned on and the gate of the first gate circuit is opened. Therefore, even if the first gate circuit malfunctions momentarily due to a noise component or a steep voltage fluctuation component and the gate of the first gate circuit is opened, the gate of the second gate circuit is mistakenly opened. This makes it possible to significantly increase the reliability of circuit operation.

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 ensuring the safe operation against the rare short circuit. it can.

Furthermore, since the present invention is a configuration for detecting an abnormality on the secondary side by increasing the DC current on the primary side, an abnormality such as discharge from the focus pack circuit connected to the high voltage coil other than the rare short circuit is also detected, The safe operation can be performed.

Further, the rare short circuit of the high voltage coil and the circuit of the present invention for protecting it can be formed integrally with the flyback transformer, so that the circuit can be made compact and the handling thereof becomes easy. In addition, a circuit including the primary side current detection circuit, the first gate circuit, the second gate circuit, and the protection fuse for detecting and protecting the rare short circuit is formed on the primary side of the flyback transformer, that is, the low voltage coil side. Since it can be configured only by the wiring on the low-voltage coil side, the wiring work is facilitated and it is convenient for achieving AC insulation of the circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a high voltage generating circuit according to the present invention, and FIG. 2 is a circuit diagram of a rare short detection and protection circuit incorporated in a conventional high voltage generating circuit. 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, 26 …… High voltage coil, 27 …… Braun tube, 28 ……
Anode, 30 ... Focus pack, 31 ... Resistor, 32
...... Protective fuse, 33 ...... Detection resistor (first gate circuit), 34 ...... PNP transistor, 35 ...... First smoothing capacitor, 36 ...... Input power supply, 37,38,39 ...... Resistor , 40 ...
… Second gate circuit, 41 …… Thyristor, 42 …… Second smoothing capacitor.

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 in series to the low-voltage end side of a low-voltage coil that constitutes a flyback transformer, a primary-side current detection circuit that detects a primary-side direct current flowing through the low-voltage coil, and this primary-side current A first gate circuit that opens a gate and outputs an operating current when the current capacity detected by the detection circuit exceeds a reference value; and a gate opening time of the first gate circuit that receives this operating current and is set And a second gate circuit which opens the gate when a time is exceeded and sends a fusing current to the protective fuse to blow the protective fuse. High voltage generating circuit, characterized in that the primary-side current detection circuit and a first gate circuit a second gate circuit are both formed on the low-voltage coil of the flyback transformer.