JPH0681263B2 - 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.

Therefore, although the quality of the high-voltage coil is sufficiently controlled so that such a rare short circuit does not occur, it is expected that a minute defective portion may be overlooked and used as a good product. If a defective product is used, a serious accident such as a fire will be caused as described above.

In recent years, in order to prevent accidents such as fires due to rare shorts, a circuit for detecting rare shorts has been provided, and measures have been taken to stop the circuit operation immediately when a rare short is detected by this circuit. Has been done.

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.

Further, the circuit shown in FIG. 3 surely 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 the circuit, and the horizontal oscillation circuit is erroneously When 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-mentioned conventional problems, and an object thereof is to detect an abnormality of a rare short circuit with a high sensitivity with a simple circuit configuration, and It is an object of the present invention to provide a high voltage circuit capable of holding a stopped state of the circuit operation of the flyback transformer by providing a latch function when detected.

[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 protection fuse connected to the low voltage end side of the low voltage coil forming the flyback transformer, an input power supply connected to the protection fuse, a first voltage applying unit and a second voltage applying unit. A gate circuit for opening a gate to supply a fusing current to a protective fuse when a voltage between the first voltage applying section and the second voltage applying section exceeds a trigger voltage, and a primary circuit flowing through the low voltage coil. A primary side current detection circuit that detects a side current and applies a voltage corresponding to the detected current value between the first voltage applying section and the second voltage applying section of the gate circuit. And increasing the voltage between the first voltage applying section and the second voltage applying section of the gate circuit by the amount of the voltage decrease of the input power source caused by the rare short circuit of the high voltage coil forming the flyback transformer. And a voltage smoothing circuit for removing a steep noise fluctuating voltage applied between the first voltage applying section and the second voltage applying section of the gate circuit to prevent malfunction of the gate circuit. It is characterized by having.

[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. This increased primary side current is detected by the primary side current detection circuit, and a voltage corresponding to this detected current is applied between the first voltage application section and the second voltage application section of the gate circuit. Further, when a rare short circuit occurs in the high voltage coil, energy is consumed in this rare short circuit portion. Since this consumed energy is supplied from the input power supply, the power supply voltage of the input power supply is reduced. The reduced voltage of the input power source is applied by the sensitivity increasing circuit in the direction of increasing the voltage between the first voltage applying section and the second voltage applying section of the gate circuit.
Therefore, when the short circuit of the high voltage coil progresses,
The voltage between the first voltage applying section and the second voltage applying section of the gate circuit quickly exceeds the trigger voltage. When the voltage exceeds the trigger voltage, the gate circuit turns on to open the gate, and the protective fuse is opened. A fusing current is applied. 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 applies a sawtooth current to the horizontal deflection coil 17 in cooperation with the tamper diode 15. 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 the focus pack 30 is composed of a resistor 31, a variable resistor VR _F for adjusting the focus voltage, and a variable resistor VRs for adjusting the screen voltage.
The end of the series connection body of 1, VR _F and VRs on the side of the resistor 31 is connected to the cathode side of the high-voltage rectifier diode 21, and the end on the side of the variable resistor VRs 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 protection fuse 32, a primary side current detection circuit 33, a thyristor 34 as a gate circuit, a smoothing capacitor 35 as a voltage smoothing circuit, a resistor 37, and a sensitivity up circuit 40. And, the primary side current detection circuit 33 is a resistor
The sensitivity increasing circuit 40 includes an input power supply 36 and resistors 38 and 41.

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 a resistor.
It is connected to one end of 43. The other end of the resistor 43 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 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. The protection fuse 32 and the resistor are provided on the cathode side of the thyristor 34 as the first voltage applying section.
It is connected to the connection part with 43. Further, one end of a resistor 37 is connected to the gate side of the thyristor 34 as the second voltage applying section, one end of a resistor 38 is connected to the other end of the resistor 37, and the other end of the resistor 38 is connected to the resistor 38. The other end of is connected to ground. The resistor 37, 38 is connected to the resistor
One end of 41 is connected and the other end of the resistor is connected to the input power supply 36.
Is connected to the connection part of the resistor 43.

In the present embodiment configured as described above, during normal operation without abnormalities such as rare short circuit in the high voltage coil 26,
The gate of thyristor 34 is closed and the voltage V _GKO across the gate and cathode of thyristor 34 is
If the resistance value of 43 is R ₁ , the resistance value of the resistor 41 is R ₃ , and the resistance value of the resistor 38 is R ₄ , then V _GKO = I _BO R ₁ − {R ₃ / (R ₃ + R ₄ )} E _BO ... (1)

However, I _BO is a low-voltage coil 2 under normal conditions without rare shorts.
2 is the value of the primary side current I _B flowing through 2, and E _BO is the value of the power supply voltage E _B of the input power supply 36 in a normal state without a rare short circuit. That is, the primary side current flowing through the low voltage coil 22 has its current capacity converted into a voltage value by the resistor 43 of the primary side current detection circuit 33, and is detected as the value I _BO R ₁ of the first term on the right side of the equation (1). To be done. Further, the power supply voltage E _BO of the input power supply 36 is resistance-divided by the resistors 41 and 38, and the divided voltage shown in the second term on the right side of the equation (1) is the voltage between the gate and the cathode of the thyristor 34. The voltage is applied in the direction of decreasing the voltage, that is, in the direction of decreasing the voltage on the gate side of the thyristor 34. The voltage between the gate and cathode of this thyristor 34
V _GKO is lower than the operating voltage of the thyristor 34, that is, the trigger voltage when the gate of the thyristor 34 is opened, when there is no abnormality such as a rare short circuit on the high-voltage coil 26 side, so the thyristor 34 is in the off state. And the gate remains closed. In this case, in the present embodiment, the sensitivity increasing circuit 40 resistance-divides the power supply voltage E _BO of the input power supply 36 and acts in the direction of lowering the gate-cathode voltage of the thyristor 34. Even if a voltage change is applied, the gate-cathode voltage does not exceed the trigger voltage, and the thyristor 34 does not malfunction to open the gate.

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 high voltage coil 26,
Energy consumption increases in the short-circuited 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. Since this short-circuit energy P is supplied from the input power supply 36, when a rare short-circuit occurs, the primary side current I _B is Δ.
Increase by I _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 + △ I _B On the other hand, since the input power supply 36 has only a limited current capacity, if the primary side current I _B increases due to a rare short circuit, the output voltage E _{B of the} input power supply 36 will increase. Is from a few percent to a few tens of percent
Decrease. Power supply voltage E _B under normal condition without rare short circuit is E
And _BO, when the decrease in the E _B during short circuit and _{△ E B, E B = E} BO - represented by △ E _B.

Therefore, when the short circuit occurs in the high-pressure coil 26 of the flyback transformer, the gate-cathode voltage V _GK is V _GK = I _B R ₁ of the thyristor 34 at that time _{- {R 3 / (R 3} + R 4)} E _{B = (I BO + △ I} B) R 1 - a _{- (△ E B E BO)} {R 3 / (R 3 + R 4)}. In other words, when a rare short circuit occurs, the current on the primary side
Increase in I _B ΔE _B voltage detection component ΔI _B R ₁ and input power supply 36 voltage decrease ΔE _B resistance division component {R ₃ / (R ₃ + R ₄ )} ΔE _B
Is applied in the direction of increasing the voltage between the gate and cathode of the thyristor 34, and when V _GK exceeds the trigger voltage of the thyristor 34, the gate is opened and the fusing current is applied to the protective fuse 32. Thus, upon the detection of short circuit not only increase the primary-side current I _B, because in addition to between the gate and cathode of the thyristor voltage reduction component of the input power source 36 by resistance division, a layer short occurs In this case, the gate-cathode voltage V _GK of the thyristor 34 quickly exceeds the trigger voltage and the gate of the thyristor 34 is opened quickly.

By the way, a rare short circuit occurred in the high voltage coil 26, and V _GK
When the voltage exceeds the trigger voltage of thyristor 34,
34 turns on, but once the thyristor 34 turns on and the gate opens in this way, the pulse generated between the high-voltage side terminal 23 of the low-voltage coil 22 and the intermediate tap 25 is short-circuited. , The coil winding portion N ₁₁ between the terminals 23 and 25 of the low voltage coil 22, the thyristor 34, and the protective fuse 3
A large fusing current flows in the route of the closed circuit formed by 2 and the protective fuse 32 blows. As a result, the primary side current supplied from the input power supply 36 to the horizontal deflection output circuit 12
The supply of I _B 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 ignition from the flyback transformer 20 are prevented in advance.

In general, the trigger voltage that is the reference for the ON operation of the thyristor 34 decreases almost linearly as the temperature rises. If this trigger voltage drops, even if a rare short circuit does not occur, if the gate-cathode voltage V _GKO during normal operation increases slightly within the allowable range, this V _GKO will exceed the trigger voltage of thyristor 34 and the same thyristor will be generated. The problem of malfunction that the gate of 34 is opened occurs. In the present embodiment, the sensitivity increasing circuit 40 acts in the direction of reducing V _GKO as described above and works in the direction of avoiding malfunction, but in order to prevent malfunction more surely, the resistor 41 is replaced by a positive temperature coefficient thermistor or By using an element such as a temperature sensitive resistor whose resistance value increases as the temperature rises, almost complete temperature compensation for the thyristor 34 can be achieved.

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

In the circuit of FIG. 1, the focus pack is placed on the high voltage coil 26 side.
30 is provided, but the circuit of this focus pack 30
For example, also increases the current I _B of the primary side when that caused a metal or the like and short in its vicinity, the thyristor
The ON operation of 34 opens the gate, and the protective fuse 32 is also 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 configured by the thyristor 34, but this gate circuit does not necessarily have to be configured by using the thyristor 34, and other appropriate circuit element, for example, as shown in FIG. Alternatively, a transistor circuit may be used.

[Advantages of the Invention] As described above, the present invention combines the increase of the primary side current and the decrease of the power supply voltage of the input power supply when a rare short circuit occurs in the high voltage coil of the flyback transformer, and Since it is configured to detect an abnormality of a rare short circuit, the detection sensitivity of the rare short circuit can be remarkably improved as compared with the method of detecting the rare short circuit by simply using only the increase in the current on the primary side.

Further, according to the present invention, since the number of parts of the circuit element is small, the circuit configuration is extremely simplified, the device manufacturing can be facilitated and the device cost can be reduced, and the reliability of the circuit operation can be improved. Is possible. Further, in the present invention, since the sawtooth component and the steep voltage fluctuation component are removed by the voltage smoothing circuit, the operation of the gate circuit becomes accurate, and the safety against a rare short circuit or the like can be more reliably achieved. The operation reliability is also higher.

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 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, 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, the circuit for detecting and protecting the rare short is the primary side of the flyback transformer,
That is, since it can be configured only by the connection on the low-voltage coil side, there is no need to add a new terminal to the flyback transformer, and in addition, AC insulation of the high-voltage generation circuit is facilitated.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a high voltage generating circuit according to the present invention, FIG. 2 is a circuit diagram showing another example of a gate circuit, and FIG.
FIG. 1 is a circuit diagram for detecting and protecting a rare short 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, 25 …… Middle tap, 26 …… High voltage coil, 27 ……
CRT, 28 …… Anode, 30 …… Focus pack, 31 …… Resistor, 32 …… Protective fuse, 33 …… Primary side current detection circuit, 34 …… Thyristor, 35 …… Smoothing capacitor, 36 …… Input power supply , 37, 38 ... Resistor, 40 ... Sensitivity up circuit, 41 ... Resistor, 43 ... Resistor.

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 protection fuse connected to the low voltage end side of a low voltage coil forming a flyback transformer, an input power supply connected to the protection fuse, a first voltage application section and a second voltage application section. A gate circuit for opening a gate to supply a fusing current to a protective fuse when a voltage between the first voltage applying section and the second voltage applying section exceeds a trigger voltage, and a primary side flowing through the low voltage coil. A primary side current detection circuit that detects a current and applies a voltage corresponding to the detected current value between the first voltage application unit and the second voltage application unit of the gate circuit; The amount of voltage decrease of the input power source caused by the rare short circuit of the high voltage coil forming the IBAC transformer is increased in the direction of increasing the voltage between the first voltage applying unit and the second voltage applying unit of the gate circuit. And a voltage smoothing circuit for preventing a malfunction of the gate circuit by removing a sharp noise fluctuating voltage applied between the first voltage applying section and the second voltage applying section of the gate circuit. High voltage generation circuit characterized by being.