JPH0744646B2 - 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.

[Prior Art] A 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 caused by 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. 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 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. 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.

The circuit shown in FIG. 2 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 in series 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 application section and a second voltage A low-voltage coil, and a gate circuit that includes an application section and opens a gate to supply a fusing current to a protective fuse when a voltage between the first voltage application section and the second voltage application section exceeds a trigger voltage. A primary side current that detects a flowing primary 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. An output circuit, a current branch circuit for branching the current from the input power supply with the current flowing to the primary side current detection circuit, and a sensitivity adjustment voltage is generated using the current flowing through this current branch circuit. A sensitivity increasing circuit that applies a voltage between the first voltage applying unit and the second voltage applying unit of the gate circuit in a decreasing direction, and a first voltage applying unit and a second voltage applying unit of the gate circuit. And a voltage smoothing circuit for preventing a malfunction of the gate circuit by removing a steep noise fluctuation voltage applied between the two.

[Action]

In the present invention configured as described above, the current from the input power source of the high voltage generation circuit is branched into the path toward the primary side current detection circuit and the current toward the current branch circuit. Then, the current flowing to the primary side current detection circuit is converted into a voltage value and detected by the detection circuit, and the detected voltage is applied between the first voltage application section and the second voltage application section of the gate circuit.

On the other hand, for the current flowing to the current branch circuit, a sensitivity adjustment voltage is generated by, for example, a resistor of the sensitivity increasing circuit, and this sensitivity adjustment voltage is generated between the first voltage applying section and the second voltage applying section of the gate circuit. Is applied in the direction of decreasing the voltage.

During normal operation in which there is no rare short circuit in the high voltage coil of the flyback transformer, the voltage between the first voltage applying section and the second voltage applying section of the gate circuit tends to decrease due to the application of the sensitivity adjustment voltage. Therefore, even if the voltage between the first voltage applying section and the second voltage applying section fluctuates within the allowable range, it does not exceed the trigger voltage, and the gate circuit maintains the off state.

On the other hand, when a rare short circuit occurs in the high voltage coil,
The primary current flowing through the low voltage coil increases rapidly. As a result of the sudden increase in the primary side current increasing the detection voltage output from the primary side current detecting circuit, the voltage between the first voltage applying section and the second voltage applying section of the gate circuit promptly changes the trigger voltage. Cross over. When the trigger voltage is exceeded, the gate circuit is turned on to open the gate, and a fusing current is applied to the protective fuse. The protective fuse is blown by the blowing current, and the operation of the flyback transformer is stopped immediately.

〔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 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 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 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 protective fuse 32, a detection resistor 33 as a primary side current detection circuit, an input power supply 36, a thyristor 34 as a gate circuit, and a smoothing capacitor 35 as a voltage smoothing circuit.
, Resistors 37, 38, 39, sensitivity resistor 40, and capacitor 41
And a 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 connected to one end of the detection resistor 33. The other end of the detection resistor 33 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 cathode side of the thyristor 34 as the first voltage application section is connected to the connection section between the protective fuse 32 and the detection resistor 33. Also, a thyristor
One end of a resistor 37 is connected to the gate side of the second voltage applying unit of 34, and the other end of the resistor 37 is connected to the resistor.
One end side of 38 and one end side of the sensitivity resistor 40 are commonly connected, and the other end side of the sensitivity resistor 40 is connected to the anode of the input power supply 36. The other end of the resistor 38 is connected to the anode of the diode 42 via the resistor 39, and the cathode side of the diode 42 is connected to the intermediate tap 25 of the low voltage coil 22. A capacitor 41 is connected between the other end of the resistor 38 and the other end of the sensitivity resistor 40. The input power source
36 to sensitivity resistor 40, resistor 38, resistor 39, diode
The path toward the intermediate tap 25 of the low-voltage coil 22 via each of the 42 forms a current branch circuit, and the thyristor 34 passes from the output end of the sensitivity resistor 40 to the resistor 37.
The circuit that reaches the gate of is a sensitivity up circuit.

In the present embodiment that is configured as described above, the current I _B at the time of operation of the circuit toward the low-voltage side terminal 24 of the low voltage coil 22 current through the protection fuse 32 from the sense resistor 33 from the input power source 36, the current It branches to a current i ₂ that goes to the intermediate tap 25 of the low-voltage coil 22 via the branch circuit. Then, the current capacity flowing through the primary side is converted into the voltage value of I _B R ₁ by the detection resistor 33 and detected (R ₁ is the resistance value of the detection resistor 33), and this detection voltage I _B R ₁ is the smoothing capacitor. The noise component and the abrupt voltage fluctuation component are removed by 35 and are applied between the gate and cathode of the thyristor 34. On the other hand, the current i ₂ flowing through the voltage branch circuit passes through the sensitivity resistor 40 to generate a sensitivity adjustment voltage of i ₂ R ₂ (R ₂ is the resistance value of the sensitivity resistor 40). This sensitivity adjusting voltage is smoothed by the capacitor 41 and applied to the gate of the thyristor 34 in the direction of decreasing the gate-cathode voltage of the thyristor 34, in this embodiment. As a result, the gate-cathode voltage of thyristor 34
V _GK is V _GK = I _B R ₁ −i ₂ R ₂ .

During normal operation in which there is no abnormality such as a rare short circuit in the high-voltage coil 26, the gate-cathode voltage V _GK of the thyristor 34 is smaller than the trigger voltage of the thyristor 34, so the thyristor 34 is turned off and the gate is closed. In this case, since the sensitivity adjustment voltage i ₂ R ₂ is applied in the direction of decreasing the gate-cathode voltage V _GK of the thyristor 34, V _GK is triggered even if the voltage applied to the gate side of the thyristor 34 slightly changes. The voltage does not exceed, and the thyristor 34 maintains the off state in a stable manner.

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 flowing from the input power supply 36 to the detection resistor 33 side increases by ΔI _B. In other words, assuming that the current on the primary side under normal conditions without rare shorts is I _BO , the current on the primary side I _B during this rare short will be
Is represented as follows.

I _B = I _BO + ΔI _B Therefore, when a rare short circuit occurs in the high voltage coil 26 of the flyback transformer, the gate-cathode voltage V _GK of the thyristor 34 at that time is V _GK = I _B R ₁ −i ₂ R ₂ = a _{(I BO + ΔI B) R} 1 -i 2 R 2. In this case, the current i ₂ flowing in the current branch circuit if a layer short occurs even somewhat increases, the increment of the i ₂ is
It is sufficiently small compared to the increase in I _B , so the increase in i ₂ is almost negligible. That is, when a rare short circuit occurs, the voltage ΔI _B R _{1 corresponding} to the sudden increase in the detection voltage is added in the direction of increasing the gate-cathode voltage of the thyristor 34, and V _GK quickly exceeds the trigger voltage of the thyristor 34. Turn on the thyristor 34 and open the gate. Thus, once the thyristor 34 is turned on and the gate is opened,
Winding part between high-voltage side terminal 23 of low-voltage coil 22 and intermediate tap 25
The pulse generated between N ₁₁ is short-circuited, and the coil winding portion N ₁₂ between the terminals 24 and 25 in the low voltage coil 22, the thyristor 34, and the protective fuse 32 form a closed circuit. A large fusing current flows in the route, 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.

In the present embodiment, since the sensitivity adjustment voltage i ₂ R ₂ generated by the sensitivity increasing circuit is applied to the gate side of the thyristor 34, the voltage between the gate and the cathode of the thyristor 34 is reduced, Gate of thyristor 34
The resistance value of the detection resistor R ₁ can be increased by the amount that the voltage between the cathodes is reduced. Thus, the sense resistor
By increasing the 33 resistance of, it is possible to detect a voltage corresponding to an increase of the primary-side current I _B due to the short circuit as a large voltage, it is possible to increase the detection sensitivity of the short circuit effectively . Further, during normal operation in which rare short circuit does not occur, the sensitivity adjustment voltage generated by the sensitivity resistor 40 acts in the direction of decreasing the gate-cathode voltage of the thyristor 34, so that the gate side of the thyristor 34 may be slightly changed. Even if the voltage fluctuation occurs, the gate-cathode voltage does not exceed the trigger voltage to open the gate, and the problem of malfunction of the thyristor 34 does not occur.

By the way, the trigger voltage that is the reference for the ON operation of the thyristor 34 decreases almost linearly as the temperature rises. If the trigger voltage drops, even if a rare short circuit does not occur, if the gate-cathode voltage V _GK during normal operation increases slightly within the allowable range, this V _GK will exceed the trigger voltage of the thyristor 34 and The problem of malfunction that the gate of 34 is opened occurs. In the present embodiment, the sensitivity increasing circuit acts to reduce V _GK as described above and acts to avoid malfunction, but in order to prevent malfunction more reliably, the resistor 38 should be set to a positive temperature coefficient thermistor or sense resistor. By using an element such as a temperature resistor whose resistance value increases as the temperature rises, almost complete temperature compensation for the thyristor 34 can be achieved.

In the circuit shown in FIG. 1 of the present embodiment, since the current branch circuit is provided, even after the thyristor 34 opens the gate and the protective fuse 32 is melted, the low voltage coil passes through the current branch circuit from the input power source 36. The current i ₂ flows to the side of the intermediate tap 25 of 22. However, this current i ₂ is due to the sensitivity resistor 40 and the resistor 38.
Has a sufficiently large resistance value that only a small amount of current flows, and there is no problem that the flyback transformer 20 is operated by this i ₂ .

According to the present embodiment described above, 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, 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, the case of the focus pack 30 has a hole or the like to cause insulation failure. etc and also increases the current I _B of the primary side when the circuit of the focus pack 30 as caused the discharge, 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 short circuit of the high voltage coil 26 but also the high voltage side abnormality such as discharge from 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 protective fuse is blown by the fuse, the safety due to the 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, although the gate circuit is configured by the thyristor 34 in the above embodiment, this gate circuit does not necessarily have to be configured by using the thyristor 34, and is configured by combining other appropriate circuit elements, for example, a transistor circuit. You may.

Further, in the above embodiment, the current i ₂ branched from the input power source 36 is supplied to the intermediate tap 25 of the low voltage coil 22 by the current branch circuit.
However, it is not always necessary to connect the output end of the current branch circuit to the intermediate tap 25 of the low-voltage coil 22, and connect the output end of this current branch circuit to another part of the primary side of the flyback transformer 20. May be.

〔The invention's effect〕

As described above, in the case where a rare short circuit occurs in the high voltage coil of the flyback transformer, the increase in the primary side current is converted into a voltage by the primary side current detection circuit and detected, and the detected voltage is Based on this, the gate of the gate circuit is opened to apply a fusing current to the protective fuse, and the operation of the flyback transformer is stopped by blowing the protective fuse. It is possible to reliably perform the operation. Moreover, in the detection of this rare short, since the sensitivity increasing circuit is provided in the present invention, the detection system of the rare short is dramatically improved, and when a rare short occurs, it can be detected quickly and its safety can be improved. The excellent effect that the measures can be taken early is obtained. Moreover,
The sensitivity increasing circuit uses the current flowing through the current branching circuit to generate a sensitivity adjusting voltage, and applies this sensitivity adjusting voltage in the direction of decreasing the voltage between the first and second voltage applying portions of the gate circuit. During normal operation without a rare short circuit, even if some voltage fluctuation occurs on the gate side of the gate circuit, it does not exceed the trigger voltage of the gate circuit, which causes the gate circuit to malfunction and open the gate, and the protective fuse opens. The problem of fusing can be solved, and the circuit operation can be stabilized.

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 such as discharge from a focus pack circuit connected to a voltage coil other than a rare short circuit is also detected, May perform safe operation.

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 it is easy to achieve AC insulation of the high voltage generation 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 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 …… Detecting resistor, 34 …… Thyristor, 35 …… Smoothing capacitor, 36…
… Input power supply, 37,38,39 …… resistor, 40 …… sensitivity resistor,
41 ... Capacitor, 42 ... Diode.

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 a high voltage generating circuit, a protection fuse connected in series to the low voltage end side of a low voltage coil that constitutes a flyback transformer, an input power supply connected to this protection fuse, a first voltage application section and a second voltage application. 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 the low voltage coil. Primary-side current detection circuit that detects a primary-side 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 A current branch circuit for branching a current from an input power source with a current flowing to the primary side current detection circuit, and a sensitivity adjustment voltage is generated by using a current flowing through the current branch circuit, and the sensitivity adjustment voltage is generated by the gate circuit. Between the first voltage applying section and the second voltage applying section of the gate circuit, and a sensitivity increasing circuit that applies a voltage between the first voltage applying section and the second voltage applying section in a decreasing direction. And a voltage smoothing circuit that removes a sharp noise fluctuation voltage applied to the gate circuit to prevent malfunction of the gate circuit.