JPH0467833B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to high-voltage direct current generated at the secondary output end of a flyback transformer in television receivers and the like and applied to the anode electrode of a cathode ray tube (hereinafter referred to as CRT). This relates to voltage stabilization circuits.

BACKGROUND ART Conventionally, there was a circuit of this type as shown in FIG. In the figure, a high-voltage output circuit 1 normally has a circuit configuration similar to a horizontal deflection output circuit (not shown) in a television receiver, and drives a high-voltage output transistor with a horizontal drive pulse voltage, and operates during the retrace period. Generates a flyback pulse voltage that resonates in the resonant coil and resonant capacitor.
This flyback pulse voltage is applied to one end of the primary winding 2a of the flyback transformer 2. A power supply voltage is applied to the other end of the primary winding 2a of the flyback transformer 2 via a voltage control circuit 3. High voltage rectifier diodes 4a,
4b are connected in series, and the high voltage DC voltage led out to the cathode end of the diode 4a, which is the secondary side output end (high voltage side end), is supplied to the anode electrode of the CRT 5. ABL (automatic brightness limiter) (not shown) is installed at the low voltage side end of the secondary winding of flyback transformer 2.
A detection voltage is applied from the circuit.

Detection resistors 6 and 7 are connected in series between the secondary output terminal of the flyback transformer 2 and the ground.
At the voltage dividing point, which is the common connection point of both resistors 6 and 7,
A voltage corresponding to the high-voltage DC voltage applied to the anode electrode of the CRT 5 is generated, and this voltage becomes a comparison input of the comparison amplifier circuit 8. The comparison amplifier circuit 8 has its comparison input terminal grounded via an integrating capacitor 9, and compares the voltage obtained by dividing the voltage of the detection resistors 6 and 7 with the reference voltage given by the DC power supply 10. Then, the voltage control circuit 3 is operated to change the primary side voltage of the flyback transformer 2 according to the comparison result.

Next, the operation of the circuit having such a configuration will be explained. The flyback pulse voltage generated by the high voltage generating circuit 1 is transmitted from the primary side to the secondary side of the flyback transformer 2, rectified into high voltage by diodes 4a and 4b, and applied to the anode electrode of the CRT 5. Here, when the brightness of CRT5 becomes brighter,
As the beam current of CRT 5 increases, due to the regulation characteristics of flyback transformer 2,
The high voltage DC voltage applied to the anode electrode of the CRT 5 decreases. This voltage change is caused by the detection resistors 6 and 7.
The divided voltage becomes the comparison input of the comparison amplifier circuit 8,
compared to a reference voltage. If the comparison input voltage is lower than the reference voltage, the comparison amplifier circuit 8 operates the voltage control circuit 3 to increase the voltage supplied to the high voltage output circuit 1.

Now, if the supply voltage to the high voltage output circuit 1 is V _CC , then the flyback pulse voltage of the high voltage output circuit 1 is
V _CP is expressed as V _CP =V _CC {2π(t _H /t _R −1)+1}. Here, t _H is the horizontal scanning period, and t _R is the horizontal scanning retrace period. Therefore, by increasing the supply voltage V _CC to the high voltage output circuit 1, the output voltage of the flyback transformer 2 increases.
This means that the high DC voltage applied to the anode electrode of the CRT 5 can be kept constant. Also, CRT
When the beam current of 5 decreases and the anode voltage of CRT 5 increases, the above-mentioned reverse operation will result in:
This means that the high-voltage DC voltage can be held constant.

In the above-mentioned high voltage stabilization circuit, normally,
Since the high voltage DC voltage applied to the anode electrode of the CRT5 is as high as 25KV to 30KV, the detection resistors 6 and 7
The resistance values are limited to around 300 MΩ for the detection resistor 6 and around 100 MΩ for the detection resistor 7 in order to suppress increases in reactive current consumption and heat generation. For this reason, the input impedance at the comparison input terminal of the comparison amplifier circuit 8 becomes considerably high, and a flyback pulse jumps to the comparison input terminal of the comparison amplifier circuit 8 due to induction from the flyback transformer 2, and as a result, the high voltage stabilizing circuit is activated. This will cause malfunction. In order to prevent this malfunction, an integrating capacitor 9 is inserted between the comparison input terminal of the comparison amplifier circuit 8 and the ground, and a measure is taken to remove high-frequency components by the action of the integrating capacitor 9.

However, in the conventional circuit configured in this way, the integration capacitor 9 is connected between the comparison input terminal of the comparison amplifier circuit 8 and the ground, so that transients in the high voltage DC voltage applied to the anode electrode of the CRT 5 are prevented. The drawback was that it could not adequately follow changes in the market.

SUMMARY OF THE INVENTION The present invention has been made to eliminate the drawbacks of the conventional ones as described above, and provides a high-voltage stabilizing circuit for CRTs that can follow transient changes in the high-voltage DC voltage applied to the anode electrode of the CRT. The purpose is to provide.

In the high-voltage stabilizing circuit for CRT according to the present invention, the detection means for detecting the variation with respect to a predetermined reference voltage in the high-voltage DC voltage generated at the secondary output terminal of the flyback transformer has a current amplifier configuration using an operational amplifier. As a result, the input end of the detection means on the high voltage detection side is virtually grounded.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which parts equivalent to those in FIG. 2 are designated by the same symbols. In the figure, flyback transformer 2
A detection resistor 6 and a constant current source 11 are connected in series between the secondary output terminal and the ground, which is a reference potential point.
The CRT5's anode voltage detection method is a current transfer method.
The inverting input terminal of an operational amplifier 12 is connected to the common connection point of the detection resistor 6 and the constant current source 11, and the non-inverting output terminal of the operational amplifier 12 is connected to the DC power supply 10.
A predetermined reference voltage is applied thereto, and an inverting comparison amplifier 14 having a current amplifier configuration has a feedback resistor 13 connected between an inverting input terminal and an output terminal. The rest of the structure is the same as that shown in FIG. 2.

Next, the operation of the circuit having such a configuration will be explained. Now, as in the conventional example, when the high voltage DC voltage applied to the anode electrode of the CRT 5 decreases, the fluctuation in the high voltage DC voltage divided by the detection resistor 6 and the equivalent impedance of the inverting input terminal of the inverting comparison amplifier 14 is compared with a reference voltage in the reaction comparison amplifier 14, and if it is lower than the reference voltage, the voltage control circuit 3 is operated to increase the voltage supplied to the high voltage output circuit 1. As a result, the output voltage of the flyback transformer 2 increases, so that the high-voltage DC voltage applied to the anode electrode of the CRT 5 can be kept constant. Further, when the anode voltage of the CRT 5 increases, the operation opposite to the above is performed.

In the conventional circuit shown in FIG. 2, the impedance at the comparison input terminal of the comparison amplifier circuit 8 is almost equal to the resistance value of the detection resistor 7, which is a high impedance. Integrating capacitor 9 is used to prevent circuit malfunctions caused by back pulses jumping.
was needed.

However, in the circuit according to the present invention described above, the impedance Z _io at the inverting input terminal of the inverting comparison amplifier 14 is Z io , where A ₀ is the open loop gain of the inverting comparison amplifier 14 and R _f is the resistance value of the feedback resistor 13. It is expressed as _io = R _f /(1+A ₀ ), and since A ₀ is sufficiently high, it can be considered that the inverting input terminal of the inverting comparison amplifier 14 is virtually grounded.

Therefore, since the input impedance of the inverting input terminal of the inverting comparator amplifier 14 is sufficiently low, the jump of the flyback pulse due to the induction from the flyback transformer 2 is small, and there is no malfunction of the circuit due to the jump, and it is possible to Since the integrating capacitor 9 used in the circuit is no longer required, the CRT
It is also possible to follow transient changes in the high-voltage DC voltage applied to the anode electrode No. 5. Note that the DC offset of the inverting comparison amplifier 14 is corrected by the constant current source 11.

Effects of the Invention As explained above, according to the present invention, an inverting comparison amplifier that detects a variation with respect to a predetermined reference voltage in a high-voltage DC voltage generated at the secondary output terminal of a flyback transformer is constructed by using an operational amplifier. By using a current amplifier configuration, the input terminal on the high voltage detection side of the inverting comparator amplifier can be considered as virtual ground, so there is no malfunction of the circuit due to jump of flyback pulses induced from the flyback transformer. , it is also possible to follow transient changes in the CRT anode voltage.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a circuit diagram showing a conventional example. Explanation of symbols of main parts, 1...High voltage output circuit,
2... flyback transformer, 3... voltage control circuit, 5... CRT (cathode ray tube), 6, 7... detection resistor, 11... constant current source, 13... feedback resistor, 14
...Inverting comparison amplifier.

Claims (1)

[Claims] 1. A detecting means for detecting a variation with respect to a predetermined reference voltage in a high-voltage DC voltage generated at the secondary output end of a flyback transformer and applied to an anode electrode of a cathode ray tube (CRT); 1 of said flyback transformer based on the output.
The high voltage stabilizing circuit for CRT is configured to control a secondary side voltage, and the detection means includes a detection resistor whose one end is connected to the secondary output terminal, and a reference potential between the other end of the detection resistor and a reference voltage. an operational amplifier whose inverting input terminal is connected to the other end of the detection resistor and to which the predetermined reference voltage is applied to the non-inverting input terminal; and an inverting input of the operational amplifier. A high voltage stabilizing circuit for a CRT, comprising a feedback resistor connected between the end and the output end.