JP2000092342A - High voltage circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a fault that takes place in some of flyback transformers in the high voltage circuit having pluralities of the flyback transformers for a display device employing a cathode ray tube. SOLUTION: A fault detection circuit 13 is provided to respective secondary windings of flyback transformers 5, 6 and outputs from the fault detection circuits are given to a protection circuit. Each fault detection circuit detects presence of a high voltage pulse and also detects a fault when a peak value of this pulse is excessive or too small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage circuit of a video display device using a cathode ray tube.

[0002]

2. Description of the Related Art Conventionally, in a display using a cathode ray tube, an abnormality detecting circuit of a high voltage circuit detects a pulse height value of a primary side of a flyback transformer (hereinafter referred to as FBT) by a secondary winding. Pulse peak value detection that outputs an abnormal signal when the pulse peak value of this secondary winding is excessive, and when the high voltage value is detected from the voltage value divided by the bleeder resistor of the high voltage distributor and this voltage becomes high Detects high voltage abnormalities with three types of detection signals: high voltage value detection that outputs an abnormal signal to the power supply, and power supply overcurrent detection that detects that the current flowing to the power supply exceeds a specified value due to the abnormality that has occurred in the high voltage output circuit are doing. When any one of the three types of abnormal signals is output, the protection circuit operates so as not to transmit the drive pulse to the high voltage output circuit.

FIG. 7 shows an example of a conventional high-voltage circuit. FIG.
In the figure, reference numeral 2 denotes a drive pulse, and reference numeral 3 denotes a protection circuit. 1 is a power supply overcurrent detection circuit, and a detection signal is a protection circuit 3
Has been transmitted to. The comparator 11 is a pulse overvoltage detection circuit of the FBT, and performs comparison with a specified voltage Vref1. The comparator 12 is a high-voltage overvoltage detection circuit, which compares the voltage with a specified voltage Vref2. The detection signals of the comparators 11 and 12 are transmitted to the protection circuit 3.

The operation of this circuit will be described. The drive pulse 2 is transmitted to the high voltage output circuit 4 through the protection circuit 3. The high-voltage output circuit 4 generates a pulse by switching using the power supply voltage supplied through the overcurrent detection circuit 1 and the drive pulse 2. Using this pulse, F
The pulse is boosted by the secondary windings of the BT 5 and the FBT 6 to generate a high voltage, and the high voltage is supplied to the cathode ray tube through the distributor 7. In the conventional high-voltage circuit, as an abnormality detection circuit, a power supply overcurrent detection that detects that an overcurrent has flowed into the power supply, and whether the high voltage value has become excessive by dividing the high voltage by the bleeder resistor in the high voltage distributor. High pressure value detection, FBT
, Three types of pulse peak value detection for detecting whether or not the pulse peak value has become excessive. Here, in the detection of the pulse peak value, each secondary winding of the FBT is diode-coupled, and an excessive pulse peak value is detected using a voltage rectified by the capacitive element 10. When any one of the above three types of signals has an abnormality, the protection circuit 3 operates so as not to transmit the drive pulse 2 to the high voltage output circuit 4.

[0005]

However, in the above-mentioned conventional configuration, the detection of the high pressure value is an abnormality detection when the high pressure value becomes high. Further, the pulse peak value detection can only detect the FBT having the highest pulse peak value among a plurality of FBTs. Therefore, in a display using a cathode ray tube having a high-voltage circuit provided with a plurality of FBTs, when an abnormality such that the pulse peak value does not become high occurs in some of the FBTs, for example, the secondary winding of the FBT When an abnormality such as short circuit occurs, no abnormal signal is output from the pulse peak value detection and the high voltage value detection. In addition, when the above abnormality occurs, a single FBT
The power supply overcurrent detection operates in the high-voltage circuit of the above. However, in the high-voltage circuit having a plurality of FBTs, the power supply overcurrent detection may not be possible if only some of the FBTs have an abnormality. There was a problem that smoke was emitted from the FBT. That is, the current high-voltage circuit has a problem that it cannot be detected even though the high-voltage circuit actually has an abnormality.

[0006]

According to the present invention, there is provided a high voltage circuit having a plurality of FBTs, wherein a secondary winding is provided with an abnormality detection circuit.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a display using a cathode ray tube, a secondary winding of each flyback transformer in a high voltage circuit using a plurality of flyback transformers. A high voltage circuit characterized by providing an abnormality detection circuit for detecting the presence or absence of a primary pulse of a flyback transformer by using a pulse output from the flyback transformer. In the high-voltage circuit used, the protection circuit can be operated when an abnormality occurs in even one of the plurality of FBTs.

According to a second aspect of the present invention, in the high-voltage circuit, each of the two flyback transformers is provided.
This is a high-voltage circuit characterized by providing an abnormality detection circuit for peak rectifying the pulse output from the next winding and detecting whether the peak rectified voltage value is within a specified value. In a high voltage circuit using a plurality of flyback transformers,
Has the effect that the protection circuit can be operated when any one of them has an abnormality.

According to a third aspect of the present invention, there is provided a power supply for supplying a high voltage output circuit, an overcurrent detection circuit for detecting an overcurrent of the power supply, a drive pulse for operating the high voltage output circuit, A protection circuit that receives the drive pulse as an input and prevents the drive pulse from being transmitted to the high-voltage output circuit when an abnormality occurs in the high-voltage circuit, a power supply voltage supplied through the overcurrent detection circuit, and an output from the protection circuit. A high-voltage output circuit that operates by a drive pulse, a flyback transformer A that receives a pulse output from the high-voltage output circuit, and a flyback transformer B that receives a pulse output from the high-voltage output circuit
A high-voltage distributor to which the outputs of the secondary winding A of the flyback transformer A and the secondary winding B of the flyback transformer B are input, and a diode having the secondary winding C of the flyback transformer A connected to the anode A, a diode B having the secondary winding D of the flyback transformer B connected to the anode, a capacitor having the cathode of the diode A and the cathode of the diode B connected to one terminal and the other terminal grounded, And the comparator A in which the cathode of the diode B and the cathode of the diode B are connected to the + terminal and the reference voltage Vref1 is connected to the − input terminal, and the detection voltage of the high voltage distributor is connected to the + terminal and the reference voltage Vref2 is connected to the − input terminal. Connected comparator B and secondary winding C of flyback transformer A
And an abnormality detection circuit having the secondary winding D of the flyback transformer B as an input, an output of the power supply overcurrent detection circuit, an output of the comparator A, an output of the comparator B, and an output of the abnormality detection circuit to the protection circuit. This is a high-voltage circuit characterized by being connected, so that in a high-voltage circuit using a plurality of flyback transformers, a protection circuit operates when one or more of the plurality of FBTs becomes abnormal. It has the effect that it can be done.

According to a fourth aspect of the present invention, there is provided a power supply for supplying a high voltage output circuit, an overcurrent detection circuit for detecting an overcurrent of the power supply, a drive pulse for operating the high voltage output circuit, A protection circuit that receives the drive pulse as an input and prevents the drive pulse from being transmitted to the high-voltage output circuit when an abnormality occurs in the high-voltage circuit, a power supply voltage supplied through the overcurrent detection circuit, and an output from the protection circuit. A high-voltage output circuit that operates by a drive pulse, a flyback transformer A that receives a pulse output from the high-voltage output circuit, and a flyback transformer B that receives a pulse output from the high-voltage output circuit
A high-voltage distributor to which the outputs of the secondary winding A of the flyback transformer A and the secondary winding B of the flyback transformer B are input, and a diode having the secondary winding C of the flyback transformer A connected to the anode A, a capacitive element A in which the cathode of the diode A is connected to one terminal and the other terminal is grounded, a diode B in which the secondary winding D of the flyback transformer B is connected to the anode, and one of the cathodes of the diode B , A capacitance element B having the other terminal grounded, an abnormality detection circuit having a cathode of the diode A and a cathode of the diode B as inputs, an output of the power supply overcurrent detection circuit, an output of the comparator A, and the comparator B and the output of the abnormality detection circuit are connected to the protection circuit, thereby providing a flyback transformer. In high-voltage circuits are pieces used,
The protection circuit can be operated when any one of the plurality of FBTs becomes abnormal.

An embodiment of the present invention will be described below with reference to the drawings. (Embodiment 1) Hereinafter, claims 1 and 3 of the present invention will be described.
An embodiment of the invention described in (1) will be described with reference to FIGS. In FIG. 1, the description corresponding to FIG. 7 is omitted.

In the first embodiment, the secondary winding is input to the abnormality detecting circuit 13 to detect whether or not a pulse is generated in all the FBTs. Either one F
If no pulse is generated in the BT, the protection circuit 3 is operated by the detection signal.

FIG. 2 shows an example of the abnormality detection circuit 13. In FIG. 2, the transistor 17 has the base of the FBT 5
The output of the next winding is connected, the collector is connected to the output of the secondary winding of the FBT 6 via the resistance element 19, and the emitter is grounded. The transistor 18 has the base connected to the output of the secondary winding of the FBT 6, the collector connected to the output of the secondary winding of the FBT 5 via the resistor element 20, and the emitter grounded. Further, the collector of the transistor 17 is connected to the anode of the diode 21, the collector of the transistor 18 is connected to the anode of the diode 22, and the cathodes of the diodes 19 and 20 are connected to the capacitor 23. This signal is used as an input to the protection circuit 3.

Next, the operation of this circuit will be described. The operation at the time of normal operation is performed with reference to FIG. The outputs of the secondary windings of FBTs 5 and 6 are pulses as shown in FIG. When the circuit is operating normally, as shown in FIG.
Since the pulses of the secondary windings of the BTs 5 and 6 have the same waveform, the transistors 17 and 18 are simultaneously turned on. Therefore, the collectors of the transistors 17 and 18 go to the L level at all times. The output obtained by performing peak rectification on this by the diodes 21 and 22 and the capacitor 23 becomes L level.

Next, FIG. 4 shows a case where only the FBT 6 becomes abnormal and no high-voltage pulse is generated. At this time, the base of the transistor 18 remains at the L level. Therefore, since the transistor 18 does not turn on, the voltage of the secondary winding of the FBT 5 is transmitted to the collector of the transistor 18 as it is. When this voltage is peak-rectified by the diode 22 and the capacitor 23, the output becomes H level, and the protection circuit 3 can be operated by this signal. That is,
The abnormality detection circuit shown in FIG. 4 forms an exclusive OR, and is a circuit that outputs an H signal only when the outputs of the FBT 5 and the FBT 6 are different.

(Embodiment 2) Hereinafter, a second aspect of the present invention will be described.
And FIG. 5 shows an embodiment of the invention described in claim 4.
This will be described with reference to FIG. In FIG. 5, the description of the portions corresponding to FIG. 7 is omitted.

In FIG. 5, for each output of the secondary winding,
The diodes 8 and 9 are connected to the capacitors 14 and 15 to perform peak rectification. The voltage obtained by peak-rectifying the output of the secondary winding of the FBT 5 with the diode 8 and the capacitor 14 is denoted by V1, and the voltage obtained by peak-rectifying the output of the secondary winding of the FBT 6 by the diode 9 and the capacitor 15 is denoted by V2. Using this voltage as an input, an abnormality is detected by an abnormality detection circuit.

FIG. 6 shows an example of the abnormality detection circuit. Voltage V1
And V2 are input to comparators 24 to 27, respectively.
Here, it is assumed that Vref3> Vref4. The comparator 24 is a comparator that detects whether V1 <Vref3 is satisfied, and the comparator 25 is a comparator that detects whether V1> Vref4 is satisfied. The peak rectified voltage V1 is V
When ref3>V1> Vref4 is satisfied, normal operation is assumed, and the output of the comparator is at the L level. V1>
In the case of Vref3, it is determined that the pulse peak value is excessive,
The output signal of the comparator 24 becomes H level. Also, V1 <
At the time of Vref4, it is determined that the pulse peak value is too small.
The output signal of the comparator 25 becomes H level. This signal is transmitted to the protection circuit 3, and the output of the high voltage is stopped. Comparator 2
Similarly, 6 and 27 are abnormality detection circuits of the FBT 6, wherein the comparator 26 is a comparator for detecting whether V2 <Vref3 is satisfied, and the comparator 27 is a comparator for detecting whether V2> Vref4 is satisfied. is there. Comparators 24 and 25
Similarly, when Vref3>V2> Vref4 is satisfied, it is determined that the circuit operates normally, and the output of the comparator is at the L level. When V2> Vref3, the output signal of the comparator 26 becomes H level. When V2 <Vref4,
The output signal of the comparator 27 becomes H level. This signal is transmitted to the protection circuit 3. As described above, the comparator 24
27 detect whether the pulse peak value is too large or too small for each FBT, and operate the protection circuit 3 by the output of the comparators 24 to 27.

[0019]

As described above, according to the present invention, in a high-voltage circuit using a plurality of flyback transformers, abnormality is detected by utilizing pulses output from the secondary windings of each flyback transformer. By providing the circuit, the protection circuit can be operated when an abnormality occurs in even one of the plurality of FBTs.

[Brief description of the drawings]

FIG. 1 is a block diagram of a high-voltage circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an abnormality detection circuit according to the first embodiment of the present invention.

FIG. 3 is an operation explanatory waveform diagram in a normal state according to the first embodiment of the present invention;

FIG. 4 is an operation explanatory waveform diagram at the time of abnormality according to the first embodiment of the present invention;

FIG. 5 is a block diagram of a high-voltage circuit according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of an abnormality detection circuit according to a second embodiment of the present invention.

FIG. 7 is a block diagram of a conventional high-voltage circuit.

[Description of Signs] 1 power supply overcurrent detection circuit 2 drive pulse 3 protection circuit 4 high voltage output circuit 5,6 flyback transformer 7 distributor 8,9,21,22,32,33,34,35 diodes 10,14, 15, 23 capacitance element 11, 12, 24, 25, 26, 27 comparator 13, 16 abnormality detection circuit 17, 18 transistor 19, 20, 28, 29, 30, 31 resistance element

Claims (4)

[Claims] In a high voltage circuit using a plurality of flyback transformers in a display using a cathode ray tube, a pulse output from a secondary winding of each flyback transformer is used to control the flyback transformer. A high voltage circuit comprising an abnormality detection circuit for detecting the presence or absence of a primary side pulse. 2. An abnormality detection circuit for peak rectifying a pulse output from a secondary winding of each flyback transformer and detecting whether or not the peak rectified voltage value is within a specified value. The high-voltage circuit according to claim 1, wherein 3. A power supply for supplying a high voltage output circuit, an overcurrent detection circuit for detecting an overcurrent of the power supply, a drive pulse for operating the high voltage output circuit, and an abnormality in the high voltage circuit when the drive pulse is input. A protection circuit that prevents a drive pulse from being transmitted to a high-voltage output circuit when a high-voltage output circuit operates, and a high-voltage output circuit that operates with a power supply voltage supplied through the overcurrent detection circuit and a drive pulse output from the protection circuit. A flyback transformer A having a pulse output from the high voltage output circuit as an input, a flyback transformer B having a pulse output from the high voltage output circuit as an input, and a secondary winding A and a flyback of the flyback transformer A A high-voltage distributor having an output of the secondary winding B of the back transformer B as an input, and a flyback transformer A
A diode A having a secondary winding C connected to the anode;
A diode B having the secondary winding D of the flyback transformer B connected to the anode; a capacitive element having the cathode of the diode A and the cathode of the diode B connected to one terminal and the other terminal grounded; The cathode of the diode B is connected to the + terminal and the reference voltage Vre
a comparator A in which f1 is connected to a negative input terminal, a comparator B in which a detection voltage of a high voltage distributor is connected to a positive terminal and a reference voltage Vref2 is connected to a negative input terminal, and a secondary winding of a flyback transformer A An abnormality detection circuit to which the line C and the secondary winding D of the flyback transformer B are input, and the output of the power supply overcurrent detection circuit, the output of the comparator A, the output of the comparator B, and the output of the abnormality detection circuit are protected. A high-voltage circuit connected to the circuit. 4. A power supply to be supplied to the high-voltage output circuit, an overcurrent detection circuit for detecting an overcurrent of the power supply, a drive pulse for operating the high-voltage output circuit, and an abnormality in the high-voltage circuit when the drive pulse is input. A protection circuit that prevents a drive pulse from being transmitted to a high-voltage output circuit when a high-voltage output circuit operates, and a high-voltage output circuit that operates with a power supply voltage supplied through the overcurrent detection circuit and a drive pulse output from the protection circuit. A flyback transformer A having a pulse output from the high voltage output circuit as an input, a flyback transformer B having a pulse output from the high voltage output circuit as an input, and a secondary winding A and a flyback of the flyback transformer A A high-voltage distributor having an output of the secondary winding B of the back transformer B as an input, and a flyback transformer A
A diode A having a secondary winding C connected to the anode;
A capacitor A in which the cathode of the diode A is connected to one terminal and the other terminal is grounded, a diode B in which the secondary winding D of the flyback transformer B is connected to the anode, and a cathode of the diode B is connected to one terminal. A capacitance element B connected and the other terminal grounded, an abnormality detection circuit having a cathode of the diode A and a cathode of the diode B as inputs,
A high-voltage circuit, wherein an output of a power supply overcurrent detection circuit, an output of a comparator A, an output of a comparator B, and an output of an abnormality detection circuit are connected to the protection circuit.