JPH05260335A - Vertical amplitude correcting circuit - Google Patents

Abstract

PURPOSE:To improve the fluctuation of the vertical amplitude caused by the anode voltage (high voltage) of a CRT with a vertical deflecting circuit of a TV receiver or a display monitor, etc. CONSTITUTION:A correction voltage generating circuit 3 generates a 2nd signal 13 only in a small current area of an anode current Ia based on a 1st signal 12 received from an anode current detecting circuit 2. The signal 13 is applied to a sawtooth waveform generating capacitor C1 via a resistance R1. Thus the amplitude of the both-end voltage of the capacitor C1 increases with reduction of the current Ia and then reduces with increase of the current Ia. Then the vertical amplitude is increased for the former case and reduced in the latter case respectively. The signal 13 is not outputted in the areas where the current Ia is kept at a prescribed level or higher and therefore the vertical amplitude is not corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical amplitude correction circuit for reducing vertical amplitude fluctuation due to fluctuation of cathode ray tube anode voltage (high voltage) in vertical deflection of a television receiver, a display monitor or the like.

[0002]

2. Description of the Related Art In deflection in a cathode ray tube, both horizontal deflection and vertical deflection vary in amplitude due to variations in cathode ray tube anode voltage. The fluctuation has a smaller amplitude both horizontally and vertically as the anode voltage increases. Further, the anode voltage fluctuates mainly because the anode current changes depending on the video signal. The conventional improvement measures to prevent this amplitude fluctuation have been mainly to improve the high voltage regulation characteristic of the flyback transformer itself or to stabilize the high voltage. Note that horizontal amplitude fluctuations may be treated separately. Due to the above-mentioned technological advances such as high voltage stabilization, the amplitude fluctuations of recent television receivers and the like have been considerably improved. However, high-pressure fluctuations have not disappeared. FIG. 2 shows an example of high voltage fluctuations with respect to the average anode current (Ia). In the figure, I2 is the maximum current (bright image) and I1 is the small current region (dark image).
, The high voltage fluctuation ΔV1 when Ia is between 0 and I1 is larger than the high voltage fluctuation ΔV2 between I1 and I2. Generally, the high-voltage fluctuation in the small current region is larger than that in the large current region, and the amplitude fluctuation is similarly large. This is largely due to the characteristics of the flyback transformer itself.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a vertical amplitude correction circuit that reduces fluctuations in vertical amplitude in the small current region.

[0004]

According to the present invention, in a vertical deflection circuit for charging and discharging a capacitor to obtain a sawtooth voltage, a cathode ray tube provided on the low potential side of a high voltage winding of a flyback transformer and flowing from the high voltage winding. An anode current detection circuit that detects an average anode current and outputs the average anode current as a first signal, and a second signal that increases or decreases in response to an increase or decrease in the first signal when the first signal has a predetermined value. A vertical amplitude correction circuit is provided which comprises a correction voltage generation circuit which generates only in the above range, and which supplements the charge of the capacitor with the second signal.

[0005]

The correction voltage generating circuit generates the second signal only in the small current region based on the first signal from the anode current detecting circuit. The second signal is applied to the charging / discharging capacitor via the resistor. With this application, the amplitude of the voltage across the capacitor increases as the anode current decreases,
On the contrary, it decreases when the anode current increases. The former increases the vertical amplitude, and the latter decreases the vertical amplitude. Since the second signal is not output in a region where the anode current is equal to or higher than the predetermined value, vertical amplitude correction is not performed.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A vertical amplitude correction circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of a vertical amplitude correction circuit according to the present invention. In the figure, 1 is a flyback transformer (FBT), 2 is an anode current detection circuit, 3 is a correction voltage generation circuit, 12 is a first signal, 13 is a second signal, R1 is a resistance, and C1 is a sawtooth wave generation. It is a capacitor. Further, 4 is an integrated circuit (IC) for a vertical deflection circuit including a lamp generator (sawtooth wave generator), a vertical drive and a vertical output, and 5 is a cathode ray tube (CR).
T) and 6 are video circuits, VDY is a vertical deflection coil of a deflection yoke, and VR1 is a vertical amplitude adjusting volume.

Next, the operation of the present invention will be described. F
The high voltage generated in the high voltage winding N2 of BT1 is applied to the anode of the cathode ray tube 5, and the anode current (Ia) flows in the direction shown in the figure. The anode current changes according to the video signal, and Ia here means the average current. Ia flows from the cathode of the cathode ray tube through the video circuit 6 and the power supply circuit (not shown), and finally from the ground to the other end (low potential side) 11 of the high voltage winding N2. Therefore, an equivalent resistance R2 and an equivalent capacitor C2 exist between the ground and the other end 11. As a result, a voltage proportional to Ia is generated across the equivalent resistance R2. The anode current detection circuit 2 outputs the voltage across the equivalent resistance R2 as a first signal 12. This voltage is generally ABL (automatic brightness limit)
It is used as a circuit reference. The first signal 12 is Ia
If is zero, it is zero, and if Ia increases, it increases proportionally (as an absolute value).

On the other hand, the fluctuation of the high voltage with respect to Ia as shown in FIG. 2 can be recognized, and the range of Ia for vertical amplitude correction can be easily determined. This range is set to I1 or less in FIG.
The first signal corresponding to I1 is V1. The correction voltage generating circuit 3 to which the first signal 12 is input generates the second signal 13 within the range of the first signal 12 described below. 0 ≦ first signal 12 ≦ V1 Outside the above range, the second signal 13 is not generated. Second signal
13 is supplied to the sawtooth wave generating capacitor C1 via the resistor R1 as shown in the figure. The basic charging / discharging action for the sawtooth wave generating capacitor C1 is performed by the lamp generator,
The amplitude of the sawtooth voltage can be adjusted and set by VR1. The second signal 13 is to increase the voltage at the time of charging within the above-mentioned fixed range among the basic charging / discharging operations, and plays a role of automatic amplitude control. That is,
When Ia is less than I1 and the high voltage rises, the vertical amplitude decreases, but the charging voltage is increased by the second signal 13 and the sawtooth amplitude of the capacitor C1 is increased accordingly. As a result, the reduced vertical amplitude is corrected to be large. Further, when Ia is less than I1 and the high pressure decreases, the vertical amplitude is corrected by the opposite action when increasing.

[0009]

As described above, according to the present invention, in the range where the high voltage fluctuation with respect to the anode current is relatively large, the vertical amplitude fluctuation caused by the high voltage fluctuation is automatically corrected. The stability of can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts showing an embodiment of a vertical amplitude correction circuit according to the present invention.

FIG. 2 is an explanatory diagram of anode current vs. high voltage characteristics.

[Explanation of symbols]

 1 Flyback transformer (FBT) 2 Anode current detection circuit 3 Corrected voltage generation circuit 4 Integrated circuit (IC) for vertical deflection circuit 12 First signal 13 Second signal R1 Resistor C1 Sawtooth wave generation capacitor VDY Deflection yoke Vertical deflection coil VR1 Vertical amplitude control knob

Claims (1)

[Claims] 1. A vertical deflection circuit for charging and discharging a capacitor to obtain a sawtooth voltage, which is provided on a low potential side of a high voltage winding of a flyback transformer and detects an average current of a cathode ray tube anode flowing from the high voltage winding. An anode current detection circuit that outputs an average anode current as a first signal, and a correction that generates a second signal that increases / decreases in accordance with an increase / decrease of the first signal only in a range in which the first signal is equal to or more than a predetermined value A vertical amplitude correction circuit comprising: a voltage generation circuit, wherein the charge of the capacitor is replenished by the second signal.