JPH02170675A - High voltage generating circuit - Google Patents

Abstract

PURPOSE:To simplify a circuit constitution and facilitate the production of the circuit by using a protective fuse, a primary-side current detecting circuit, and first and second gate circuits as principal circuit elements to constitute a circuit which detects rate short generated in a high voltage coil and protects it. CONSTITUTION:When rate short-circuit is generated in a high voltage coil 26, a primary-side current IB is increased. In accordance with this increase, a primary-side current capacity, namely, a detection voltage e1 detected by a detecting resistor 33 is increased. When this detection voltage e1 exceeds the turning-on operation voltage of a PNP transistor TR 34, the TR 34 is turned on to open the gate, and the operating current is applied to the second gate circuit from the collector side. When the TR 34 is turned on over a section of time delay due to the time constant, the gate of a thyristor 41 is opened. Then, the circuit between the anode of an input power source and the earth is shorted and a large current is made flow to a protective fuse 32 to fuse the protective fuse 32. Consequently, smoking and firing from a flyback transformer are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high voltage generation circuit equipped with a means for preventing a layer short circuit occurring in a high voltage coil of a flyback transformer.

[Conventional technology]

The high voltage generation circuit of a television receiver or CRT display device includes a flyback transformer that boosts the flyback pulse. This flyback transformer is normally subjected to a high voltage of about 30 Kv. For example, due to a manufacturing error, a short circuit occurs in the high voltage coil of the flyback transformer, and if this progresses, the flyback transformer will start to smoke.・It may ignite and lead to a major accident such as a fire.

Although the high-voltage coil has sufficient quality control to prevent such rare shorts from occurring, it is expected that minute defects will be overlooked and the product will be used as a non-defective product. When used, as mentioned above (,
This may cause a major accident such as a fire.

In recent years, in order to prevent accidents such as fires caused by such layer shorts, a layer short detection circuit has been installed, and when a layer short is detected by this circuit, the circuit operation is immediately stopped. Some improvements have been made.

FIG. 2 shows a circuit that is incorporated into a conventional high voltage generation circuit and performs a layer short detection and protection operation. This circuit detects the primary current that increases due to the layer short when a layer short occurs in the high voltage coil of the flyback transformer, and stops the horizontal oscillation circuit (not shown). In other words, under normal conditions when no layer short occurs, the primary current of the flybank transformer is approximately IA or less;
In the circuit shown, the voltage drop across resistor 1 is small, and transistor 2 remains off. On the other hand, when a layer short circuit occurs and an abnormal state occurs, the primary side current increases to about 2 A, the voltage drop across the resistor 1 increases, and the transistor 2 turns on. As a result, the voltage of capacitor 3 increases and Zener diode 4
is turned on, and at the same time, transistor 5 is also turned on. As a result, the light emitting diode inside the photocoupler 6 is driven, the transistor 7 in the non-charging part is turned on, the electric charge stored in the capacitor 8 is charged in the capacitor 9, and the X-ray protection terminal 11 of the photocoupler 10 is charged. This is to drive the horizontal oscillation circuit and stop the oscillation of the horizontal oscillation circuit. By stopping the horizontal oscillation circuit, the operation of the flyback transformer also stops, thereby preventing the occurrence of a fire or the like caused by a layer short circuit.

[Problems to be Solved by the Invention] However, as shown in Figure 2, this type of conventional circuit uses a large number of circuit parts, making the circuit complicated. There is a problem that the process becomes complicated and the cost of the device increases accordingly.

Furthermore, the circuit shown in Fig. 2 does indeed stop the horizontal oscillation circuit when a layer short occurs in the high-voltage coil, but it does not have a latch function to stop this circuit, so it may accidentally cause
If the horizontal oscillation circuit is turned on again, there is a danger that the flyback transformer will operate and the layer short circuit will progress further.

The present invention has been made in order to solve the above-mentioned conventional problems, and its purpose is to be able to detect a layer short abnormality with a circuit configuration similar to that of a vehicle in front of the vehicle, and to detect an abnormality in the case where an asyode is detected. The object of the present invention is to provide a high voltage circuit which has a latch function and can maintain a stopped state of circuit operation of a flyback transformer.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention includes a horizontal deflection output circuit that generates and outputs a flyback pulse, and a flyback transformer that boosts the flyback pulse generated by the horizontal deflection output circuit and applies the boosted output to the anode of the cathode ray tube. In a 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 current detection circuit that detects a primary current flowing through the low voltage coil, and a primary current detection circuit that detects a primary current flowing through the low voltage coil; a first gate circuit that opens the gate and outputs an operating current when the current capacity detected by the detection circuit exceeds a reference value;
In response to this operating current, when the gate opening time of the first gate circuit exceeds a set time, a second gate circuit opens the gate and applies a fusing current to the protective fuse to blow the protective fuse.
The structure is characterized in that it has a gate circuit.

[Effect]

In the present invention configured as described above, when a layer short occurs in the high voltage coil constituting the flyback transformer, the primary current flowing through the low voltage coil increases rapidly. The amount of increase in this primary current is detected by the primary current detection circuit, and when this detected current capacity exceeds a reference value, the gate of the first gate circuit is opened and the operating current is added to the second gate circuit. It will be done. The second gate circuit detects the time during which the first gate circuit opens the gate (ON operation time), and when this gate open time exceeds a set time, opens the gate and applies a blowing current to the protective fuse. Add. This blowing current blows out the protective fuse, and the operation of the flyback transformer is accordingly stopped.

〔Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the circuit configuration of a high voltage generation circuit showing one 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 layer short detection/protection circuit 14.

Among these circuits, the circuits other than the layer short detection/protection circuit 14 are known, so the description of those known circuits will be simplified.

The horizontal deflection output circuit 12 includes a horizontal output transistor 1
9, damper diode 15, and resonant capacitor 16
, a horizontal deflection coil 17 , and a three-character correction capacitor 18 . The horizontal output transistor 19 performs a switching action in response to a voltage pulse sent from a horizontal drive circuit (not shown), and applies a sawtooth wave current to the horizontal deflection coil 17 in cooperation with the damper diode 15. On the one hand, the resonant capacitor 16 and the horizontal deflection coil 17 generate flyback pulses by their resonant action, which are applied to the high voltage circuit 13.

The high voltage circuit 13 includes a flyback transformer 20 and a high voltage rectifier diode 21. High voltage side terminal 23 of the low voltage coil (-secondary coil) 22 of the flyback transformer 20
is connected to a common terminal of the horizontal deflection coil 17 and the resonant capacitor 16, and a layer short detection/protection circuit 14, which will be described later, is connected to the low voltage side terminal 24 of the low voltage coil 22.

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 high voltage rectifier diode 21.
It is connected to the anode 28 of the cathode ray tube 27 via. In the circuit of this embodiment, the high voltage rectifier diode 2
One end side of the circuit of the focus pack 30 is connected to the cathode side of the focus pack 30 . The circuit of this focus pack 30 includes a resistor 31 and a variable resistor V for adjusting the focus voltage.
R, and a variable resistor VR for adjusting the screen voltage, and each of these resistors 31. The end of the series connection body of VR, VR, on the resistor 31 side is connected to the high voltage rectifier diode 2.
1, and the end on the variable resistor VR side is connected to the ground side. In addition, high voltage coil 2
The low pressure side of 6 is ABL (Δautomatic Bright
tnessLimiter). In such a configuration, the high voltage circuit 13 boosts the flyback pulse applied from the horizontal deflection output circuit 12 using the flyback transformer 20, and further boosts the flyback pulse applied from the horizontal deflection output circuit 12 by using the high voltage rectifier diode 21.
The signal is rectified by the anode 28, and the rectified output is sent to the anode 28.
It is added to.

The layer short detection/protection circuit 14 reliably detects a layer short occurring in the high voltage coil 26 of the fly bank transformer 20 and performs safe operation thereof, and is a characteristic circuit of this embodiment. This layer short detection/protection circuit 14 includes a detection resistor 33 as a primary side current detection circuit.
, a protective fuse 32, an input power supply 36, a PNP transistor 34 as a first gate circuit, a first smoothing capacitor 35 as a voltage smoothing circuit, and a resistor 37.
, 38 and a second gate circuit 40. The second gate circuit 40 includes 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 connected to the low voltage side terminal 24 of the low voltage coil 22, and the other end of the resistor 33 is connected to one end of the protection fuse 32.

The other end of the protective fuse 32 is connected to the anode of the input power source 36. Note that the cathode of this input power source 36 is connected to ground. This input power supply 36 is provided with a power supply fuse, and in this 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. Further, the emitter side of the PNP transistor 34 is connected to a connection portion between the detection resistor 33 and the protection fuse 32.

A first smoothing capacitor 35 is connected between the base and emitter of the PNP transistor 34. A resistor 38 is connected to the collector side of the PNP transistor 34.
It is connected to ground through a series connection of 39 and 39.

The anode side of the thyristor 41 constituting 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 between the resistors 38 and 39. Furthermore, the cathode side of the thyristor 41 is connected to ground. A second smoothing capacitor 42 is connected between the gate and cathode of the thyristor 41.

In this embodiment configured as described above, when the circuit is in operation, the primary side current flows from the input power source 36 to the low voltage coil 22! , is flowing, and this current on the primary side! , is converted into a voltage of ImR+ by the detection resistor 33 and detected (R1 is the resistance value of the detection resistor 33).During normal operation when there is no abnormality such as a short circuit in the high voltage coil 26, the voltage is detected by the detection resistor 33. voltage eI (6+ −
1m R+ ) is lower than the on-operation voltage of the PNP transistor 34, the PNP transistor 34 remains off, and the thyristor 41 also remains off.

On the other hand, when a layer short occurs in the high voltage coil 26, the primary side current 1. increases.

That is, when a rare short occurs in the high voltage coil 26, energy consumption increases in the short portion. Now, if the short energy consumed per turn of rare short is q, then when rare short expands to n turns, the energy P consumed from that part is P = nq
becomes.

In this case, this short energy P is supplied from the input power supply 36, so when a layer short occurs, the primary side current 1. increases by ΔI. That is, assuming that the primary side current in a normal state with no layer short-circuit is 11 degrees, the primary-side current I6 at the time of this layer short-circuit is expressed as follows.

1m””Is. 1Δ■8 In this way, when a layer short occurs in the high voltage coil 26, the primary side current 1. is Δ1. The current capacity on the primary side, that is, the detection voltage e detected by the detection resistor 33 increases accordingly.

When this detection voltage e1 exceeds the on-operation voltage of the PNP transistor 34, the PNP transistor 34 turns on, opens its gate, and applies an operating current from the collector side to the second gate circuit. By applying this operating current, a driving voltage divided by the resistors 38 and 39 is applied to the gate of the thyristor 41, but in this embodiment, a second voltage is applied between the gate and the cathode of the thyristor 41. A smoothing capacitor 42 and a resistor 39 are connected in parallel, and a time constant determined by the second smoothing capacitor 42 and resistor 39 causes the voltage applied between the gate and cathode of the thyristor 41 to trigger the thyristor 41. There is a certain time delay before the voltage is exceeded. When the PNP transistor 34 turns off and closes the gate during this time delay, the gate voltage of the thyristor 41 does not exceed the trigger voltage, so the gate of the thyristor 41 is not opened, but during the time delay period due to the time constant. Beyond PN
When the P-type transistor 34 continues to turn on, the voltage between the gate and 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 turns on and opens its gate. Thyristor 41
When the gate of
A large current (fusing current) flows in path a that goes to the Cyrisk 41 ground, and this large current causes the protective fuse 32 to
is fused. As a result, the supply of the primary current 1 from the input power supply 36 to the horizontal deflection output circuit 12 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, heat generation at the short portion is stopped, and smoke and ignition from the flyback transformer 20 are prevented.

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 transistor 34 and
Similarly, the second smoothing capacitor 42 prevents the thyristor 41 from malfunctioning by removing noise components and steep voltage fluctuation components applied to the thyristor 41.

Furthermore, in this embodiment, the configuration is such that it takes a certain amount of time for the voltage applied between the gate and cathode of the thyristor 41 to exceed the trigger voltage of the thyristor 41 due to the time constant determined by the second smoothing capacitor 42 and the resistor 39. Therefore, even if the PNP transistor 34 malfunctions and momentarily turns on during this time, the voltage between the gate and cathode of the thyristor 41 will not exceed the trigger voltage, and the thyristor 41 will not operate. The reliability of the system will be greatly improved.

Furthermore, in the circuit shown in FIG. 1, the focus back 30 is provided on the high voltage coil 26 side, but the case of the focus back 30 may be punctured and the insulation may deteriorate.
Even if the circuit of the focus pack 30 causes a discharge with, for example, a metal chassis located nearby, the primary side current 1. increases, and the PNP transistor 34
The respective gates are opened by the ON operation of the thyristor 41, and the protective fuse 32 is similarly blown.

Therefore, in the circuit configuration of this embodiment, not only the rare short circuit of the high voltage coil 26 but also the focus pack 3
An abnormality on the high voltage side, such as a discharge from zero, is detected by an increase in the primary current, and the thyristor gate is immediately opened and the protective fuse is blown. This will be effective.

In this embodiment, once the protective fuse 32 is blown, the circuit operation of the flyback transformer 20 is latched to a stopped state. Therefore, flyback transformer 2
0 with a normal one and the protective fuse 32 is replaced, the circuit will not operate again, making it possible to more safely prevent smoke and fire accidents caused by a short circuit.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented in various ways. For example, in the above-mentioned embodiments, a circuit configuration is shown in which the high-voltage output circuit and the horizontal deflection output circuit are not separated. However, if these are separated, the horizontal deflection coil 17 and the three-figure correction capacitor 18 become unnecessary. However, even in this case, only the horizontal deflection coil 17 can be replaced with a dummy inductance.

Further, in the above embodiment, the first gate circuit is constructed using the PNP transistor 34, and the second gate circuit is constructed using the thyristor 41, but these may also be constructed using other circuit elements. good.

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

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

〔Effect of the invention〕

As explained above, the present invention uses a protective fuse connected to the low-voltage coil side, a primary current detection circuit, and each of the first and second gate circuits as main circuit elements, and uses Since the circuit consists of a circuit that detects and protects against short circuits, the number of circuit elements is extremely small, which simplifies the circuit configuration and simplifies circuit manufacturing and reduces device costs. It will be possible to achieve this together. Furthermore, since the number of parts is small as described above, the reliability of the circuit operation can be increased accordingly.

Further, in the present invention, the gate of the second gate circuit is opened when a predetermined set time has elapsed 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 momentarily malfunctions 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 will be opened by mistake. This makes it possible to significantly improve the reliability of circuit operation.

Furthermore, in the present invention, once an asyode is detected, the protective fuse is blown, so the circuit operation is latched to a stopped state, thereby further ensuring safe operation against layer shorts. can.

Furthermore, since the present invention is configured to detect an abnormality on the secondary side by an increase in current on the primary side, it is possible to detect abnormalities other than layer shorts, such as discharge from a focus pack circuit connected to a high voltage coil. Able to perform safe operation.

Further, since the circuit of the present invention for preventing rare shorts in the high voltage coil and protecting the same can be formed integrally with the flyback transformer, the circuit can be made compact and easy to handle. Moreover, the circuit for detecting and protecting the rare short is the primary side of the flyback transformer.
In other words, since it can be constructed by only connecting the wires on the low-voltage coil side, it is convenient for achieving AC insulation of the circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a high voltage generation circuit according to the present invention, and FIG. 2 is a circuit diagram of a rare-shot detection and protection circuit incorporated in a conventional high voltage generation circuit. DESCRIPTION OF SYMBOLS 1...Resistor, 2...Transistor, 3...Capacitor, 4...Zener diode, 5...Transistor, 6...Photocoupler, 7...Transistor, 8.9...・Capacitor, 10... Photocoupler,
11...X-ray protection terminal, 12...Horizontal deflection output circuit, 13...High voltage circuit, 14...Rear short detection
Protection circuit, 15... Damper diode, 16...
Resonance capacitor, 17...Horizontal deflection coil, 18...
・5-character 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...
・Protection fuse, 33...Detection resistor (first gate circuit), 34...PNP type transistor, 35...
First smoothing capacitor, 36... Input power supply, 37.3
8.39...Resistor, 40...Second gate circuit,
41... Cyrisk, 42... Second smoothing capacitor.

Claims (1)

[Claims] A high voltage generation circuit comprising a horizontal deflection output circuit that generates and outputs a flyback pulse, and a flyback transformer that boosts the flyback pulse generated by the horizontal deflection output circuit and applies the boosted output to the anode of a cathode ray tube. A protective fuse connected in series to the low voltage end side of the low voltage coil that constitutes the flyback transformer, a primary current detection circuit that detects the primary current flowing through the low voltage coil, and a primary current detection circuit that detects the primary current flowing through the low voltage coil. a first gate circuit that opens the gate and outputs an operating current when the current capacity exceeds a reference value; and a first gate circuit that receives the operating current and receives the operating current when the gate opening time of the first gate circuit exceeds a set time. and a second gate circuit that opens a gate and causes a blowing current to flow through the protective fuse to blow the protective fuse.