JPH0681261B2 - 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 operation of the flyback transformer is also stopped due to the stop of the horizontal oscillation circuit, which prevents 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 circuit is opened to blow a fusing current to the protection fuse to blow the protection fuse, and a sharp noise fluctuation voltage applied to the gate circuit is removed. A voltage compensating circuit for preventing malfunction of the gate circuit, and a temperature compensating circuit for compensating the temperature of the gate circuit, A low pressure coil, and a gate circuit, and the protection fuse is configured as characterized in that connected in series to form 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.

The reference value that determines the operating point of this gate circuit fluctuates as the temperature changes. The temperature compensating circuit suppresses the fluctuation of the reference value and ensures the accurate gate opening operation of the gate circuit.

〔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 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 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
Is 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, resistors 37, 38, 39, and a capacitor 40.
, Diode 41 and diode as a temperature compensation circuit
It consists of 42 and. Further, the primary current detection circuit 33 includes resistors 43 and 44 and the diode 42.

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 positive side of the input power source 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 has a low voltage coil 22.
Is connected to the middle tap 25 of. Also, the thyristor 32
The anode side of is connected to the anode side of the diode 41. The cathode side of the diode 41 is connected to the gate side of the thyristor 34 via a series connection body of resistors 39 and 37. The cathode side of the thyristor 34 is connected to the common connection portion of the protection fuse 32 and the resistor 43. A smoothing capacitor 35 is connected between the gate and cathode of the thyristor 34. The anode side of the diode 42 is connected to the common connection portion between the gate of the thyristor 34 and the resistor 37, and the cathode side of the diode 42 is connected to the ground side via the resistor 38. Then, one end of a resistor 44 is connected to the cathode side of the diode 42, and the other end of the resistor 44 is connected to a common connecting portion between the resistor 43 and the input power supply 36. One end of a capacitor 40 is connected to the connection between the resistors 39 and 37, and the other end of the capacitor 40 is connected to the input power source 36.
Is connected to the positive side of.

In the present embodiment configured as described above, during circuit operation, the flyback pulse applied to the intermediate tap 25 of the low voltage coil 22 is rectified by the diode 41 and stepped down by the resistor 39, It is smoothed by the capacitor 40. This is the capacitor 40 will take the voltage E ₀ which is smooth, this is the output voltage E ₀ to the position of the capacitor 40
It is equivalent to connecting the DC power supply of. Therefore,
During normal operation in which the high-voltage coil 26 has no abnormality such as a rare short circuit, the gate of the thyristor 34 is closed, and a direct current flows from the resistor 37 to the diode 42 by the voltage E ₀ .

At this time, the voltage V between the gate and cathode of the thyristor 34
_Assuming that the forward voltage of the diode 42 is V _D , the resistance value of the resistor 43 is R ₁ , and the resistance value of the resistor 44 is R ₃ , _{G G is} V _GK = I _B R ₁ −i ₁ R ₃ + V _D … ( 1)

However, I _B is the primary side current flowing through the low voltage coil 22,
i ₁ is a current flowing from the resistor 44 to the resistor 38. That is, the primary side current flowing through the low voltage coil 22 has its current capacity converted into a voltage value by the resistors 43 and 44 of the primary side current detection circuit 33 and the diode 42, and is detected as a value on the right side of the equation (1). It

The voltage V _GK between the gate and the cathode of the thyristor 34 is the voltage when there is no abnormality such as a rare short circuit on the high voltage coil 26 side.
The operating voltage of the thyristor 34, that is, the reference voltage (gate voltage as a reference value when the gate of the thyristor 34 is opened).
Trigger voltage), and therefore the thyristor 34 remains off and the gate 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 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 voltage detected by the primary side current detection circuit 33. Will increase. That is, the current on the primary side
As I _B increases, I _B R ₁ increases, and when V _GK exceeds the gate trigger voltage (operating reference voltage) of thyristor 34, the gate is opened and a blowing current is applied to protective fuse 32. .

Next, the change of i ₁ R _{3 in the} equation (1) in the circuit of this embodiment will be described. The change of i ₁ R ₃ will be described based on the equivalent circuit of the primary side current detection circuit 33 shown in FIG. 2 for the sake of simplicity.

In the equivalent circuit of FIG. 2, resistor 37 to diode 42
I _{1 is} the current flowing through the resistor 38 toward the resistor 38, and the current flowing from the resistor 37 through the diode 42 toward the resistor 44 is
I ₂ , the current flowing from the resistor 44 to the resistor 38 is I _3, and the voltage applied across the capacitor 40 is E ₀ , and the power supply voltage of the input power supply 36 is E _B , I ₂ , I ₃ Is expressed by the following equation.

I ₂ = (E ₀ −V _D ) / (R ₂ + R ₃ ) I ₃ = E _B / (R ₃ + R ₄ ), where R ₂ is the resistance value of resistor 37, and R ₄ is the resistance value of resistor 38. It is the resistance value.

Then, the current flowing through the resistor 44 i _1, to represent the voltage across the resistor 44 at _{V 3, V 3 = i 1} R 3 = (I 2 -I 1) R 3 = R 3 {E _{B / (R 3 + R 4} ) - the _{(E 0 -V D) / (} R 2 + R 3)}. Here, V _D is sufficiently smaller than E ₀ (V _D << E ₀ ), so if V _D is ignored, V ₃ = R ₃ {E _B / (R ₃ + R ₄ ) −E ₀ / (R ₂ + R ₃ )} On the other hand, when a rare short circuit occurs, the collector voltage of the horizontal deflection output circuit 12 decreases, so that both E ₀ and E _B decrease. If E ₀ and E _B both decrease at the same ratio and become K times (K <1), V ₃ at the time of a rare short circuit is V ₃ = R ₃ {KE _B / (R ₃ + R ₄ ) −KE ₀ / (R ₂ + R ₃ )} = KR ₃ {E _B / (R ₃ + R ₄ ) −E ₀ / (R ₂ + R ₃ )}, and V ₃ also decreases K times.

As described above, i ₁ R _{3 on} the right side of the equation (1), that is, V ₃ decreases at the time of a rare short circuit, and therefore increases V _GK , leading to the direction in which the thyristor 34 turns on, and only by increasing I _B. It is possible to further improve the detection sensitivity of rare shorts as compared with the detection of rare shorts.

By the way, a rare short circuit occurred in the high voltage coil 26, and V _GK
When the voltage exceeds the gate trigger voltage of the thyristor 34, the current i ₂ ′ flows into the gate of the thyristor 34 through the resistor 37 of FIG. 1 and the thyristor 34 turns on. When the thyristor 34 is once turned on and the gate is opened 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.
A large fusing current flows in the route of the closed circuit formed by the coil winding portion N ₁₁ between the terminals 24 and 25 in 22, the diode 41, the thyristor 34, and the protective fuse 32, and the protective fuse 32 blows. 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. 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.

Next, the operation of the diode 42 as the temperature compensation circuit in this embodiment will be described. In general, the gate trigger voltage, which is the on-operation voltage of thyristor 34, decreases almost linearly with increasing temperature. Even if a rare short circuit does not occur when this ON operation voltage decreases, if V _GK increases slightly within the allowable range, this V _GK exceeds the ON operation voltage of the thyristor 34 and the gate of the thyristor 34 opens. The problem of malfunction occurs. In this embodiment, a diode 42 as a temperature compensation circuit is provided in order to avoid such a post-operation of the thyristor 34. The forward voltage V _D of the diode 42 has the property of decreasing linearly as the temperature rises. Therefore, as can be seen from the equation (1), the value of V _D decreases as the temperature rises. To do. Therefore, the value of V _GK also decreased, during normal operation with no short circuit, even when the current I _B of the primary side is increased within the allowable range, V _GK is without exceeding the gate-trigger voltage of the thyristor 34 It is possible to reliably prevent malfunction of the thyristor 34, and to further improve the reliability of the gate circuit. The slope of the decrease of the voltage V _D with respect to the temperature rise of the diode 42 depends on the magnitude of the current i ₂ flowing into the diode 42. Therefore, the resistance value R ₂ of the resistor 37 is changed to the ON operation with respect to the temperature rise of the thyristor 34. By adjusting to the slope of the voltage decrease,
It is possible to achieve almost perfect temperature compensation for the thyristor 34.

By the way, the circuit of the present embodiment shown in FIG. 1 is designed with various consideration so as to perform a preferable circuit operation. That is, by providing the resistor 39 between the diode 41 and the capacitor 40, the capacitor 40 is prevented from flowing a large current.
Is being protected. Further, by providing the diode 41 between the anode side of the thyristor 34 and the resistor 39, it is possible to prevent LC resonance from occurring due to the low voltage coil 22 and the smoothing capacitor 35, and to reduce the reverse withstand voltage of the diode 42. The effect is that it can be made into something. Furthermore, the negative side of the capacitor 40 can be connected to the ground side, but by connecting this to the positive side of the input power supply 36 as in this embodiment, the capacitor to be used
The effect is that the breakdown voltage of 40 can be reduced.

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 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 of FIG. 1, the focus pack 30 is provided on the side of the high voltage coil 26. However, even when the circuit of the focus pack 30 is short-circuited with a metal or the like in the vicinity thereof, for example. increased current I _B of the primary side, 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 the rare short circuit of the high voltage coil 26 but also the high voltage side abnormality such as the 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 opened immediately. 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 divided 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 may be configured by using another appropriate circuit element, for example, a transistor. Good.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, the present invention provides a protection fuse connected to the low-voltage coil side, a primary-side current detection circuit, a gate circuit, a temperature compensation circuit, and a voltage smoothing circuit as main circuit elements to a high-voltage coil. Since the circuit is designed to detect and protect the rare shorts that occur, the number of circuit element parts is small, which greatly simplifies the circuit configuration and simplifies circuit manufacturing and reduces device cost. It is possible to work together. 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 voltage-smoothing circuit removes the sawtooth component and the steep voltage fluctuation component.
Since the temperature of the gate circuit is compensated by the temperature compensating circuit, the operation of the gate circuit becomes accurate, the safety against a rare short circuit or the like can be ensured more reliably, and the reliability of the circuit operation becomes high.

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 wiring on the low-voltage coil side, it is also convenient in terms of 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, FIG. 2 is an equivalent circuit diagram of a primary side current detecting circuit portion in the same embodiment, and FIG. 3 is incorporated into 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 …… Primary side current detection circuit, 34 …… Thyristor, 35 …… Smoothing capacitor (voltage smoothing circuit), 36 …… Input power supply, 37,38,39 …… Resistor, 40 …… Capacitor, 41,42 …… Diode, 43,44
……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 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 a temperature compensating circuit for compensating the temperature of the gate circuit are included. Le and a high pressure generation circuit and the gate circuit, the protection fuse, characterized in that to form a closed loop are connected in series.