JPH0695608A - High-voltage stabilizing circuit in crt display device - Google Patents

Abstract

PURPOSE: To perform the high voltage stabilization of a CRT with extremely high accuracy without the need for excessive circuits. CONSTITUTION: This circuit is provided with a driving circuit 7 for generating a voltage amplitude for driving the cathode 6 of the CRT 1 in response to video signals, a low-pass filter provided with resistors R20 and R21 and a capacitor C4 for generating an output voltage from which the high frequency component of the video signals is removed, and a high voltage control circuit 4 for controlling a voltage to be applied to the anode 2 of the CRT 1 in response to the output voltage of the capacitor 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage stabilizing circuit in a CRT display device.

[0002]

CRT display devices are used as display means for personal computers and word processors, for example. For example, C used for such applications
The high voltage stabilizing circuit in the RT display device always keeps the high voltage applied to the anode constant regardless of the anode current amount (or cathode current amount) of the CRT, and suppresses the fluctuation of the anode voltage due to the change of the anode current. Thus, the fluctuation of the screen size on the CRT is suppressed. According to this high-voltage stabilizing circuit, the screen size on the CRT is always kept constant regardless of the type, brightness, and change of the displayed image. For this reason, in high voltage stabilization circuits, various applications such as reverse display, multi-window, and moving images are increasing, and further, a screen design that uses a flat square tube for a CRT to occupy the entire display area is becoming mainstream in recent years. Then it is an essential circuit.

The high voltage stabilizing circuit is roughly divided into a high voltage detecting circuit and a high voltage control circuit. Conventionally, there are the following two methods for controlling the high voltage in the high voltage stabilizing circuit.

(1) A method of detecting the high voltage itself applied to the anode and applying feedback control to the high voltage control circuit based on the detection result. (2) Detecting the cathode current amount of the CRT and using this detection result. Method for Applying Feedforward Control to High Voltage Control Circuit Based on FIG. 2 In FIG. 2, 1 is a CRT and 2 is an anode of the CRT. Reference numeral 3 denotes a flyback transformer, one end (high-voltage side end) of a secondary winding (high-voltage winding) thereof is connected to the anode 2 via a rectifying diode D1 and the other end (low-voltage side end).
Is an NPN-type transistor Q that constitutes the high-voltage control circuit 4.
1 collector. The high voltage control circuit 4 includes a transistor Q1 and four resistors R1 to R4,
The collector of the transistor Q1 is connected to a suitable positive power source (+ V) for controlling the high voltage applied to the anode 2 via the resistor R1, the emitter is grounded via the resistor R2, and the base is connected to the high voltage detecting circuit 5 Output voltage is divided by resistors R3 and R4 and applied. The high voltage detection circuit 5 is composed of an operational amplifier A1, a resistor R5 and a semi-fixed resistor R6 for adjusting the operating point, and the anode 2 via a resistor R7.
The high voltage applied to the circuit is appropriately divided by a series circuit of resistors R7, R5 and R6, and the divided voltage is obtained by the operational amplifier A1.
Is compared with a reference voltage (Vref), and the comparison result is input to the high voltage control circuit 4.

According to this structure, the high voltage applied to the anode 2 is directly detected by the high voltage detection circuit 5, and the difference between this detection value and the reference voltage is given to the high voltage control circuit 4 as the high voltage detection value. The high-voltage control circuit 4 inversely amplifies the high-voltage detection voltage from the high-voltage detection circuit 5 with the transistor Q1, and feedback-controls the high voltage at the high-voltage side end of the secondary winding of the flyback transformer 3. As a result, the high voltage applied to the anode 2 is stabilized to a steady value.

FIG. 3 shows an example of a circuit using the method (2). In FIG. 3, reference numeral 6 is a cathode of the CRT 1, and a video signal is supplied to the cathode 6 via a cathode drive circuit 7 and a black level clamp circuit 8.

The drive circuit 7 includes three resistors R8 to R10, 2
Consisting of two diodes D2 and D3, two NPN type transistors Q2 and Q3, and a PNP type transistor Q4. A video signal is input to the base of the transistor Q2 via a resistor R9, and the emitters of the transistors Q3 and Q4 A video signal to be applied to the cathode 6 is output from the connecting portion between them. The black level clamp circuit 8 includes two capacitors C1 and C2, six resistors R11 to R16, a diode D4, a PNP type transistor Q5, and an NPN type transistor Q6. The series circuit of the capacitor C1 and the resistor R11 forms a transistor. Q3 and Q
The connecting portion between the respective emitters 4 and the cathode 6 are AC-coupled. When the clamp pulse synchronized with the video signal input to the drive circuit 7 is input to the base of the transistor Q6, the transistor Q6 is turned on and the transistor Q5 is turned on, whereby the power supply voltage (+ B) is changed to the resistor R12. And the resistors R14, R15 and R17 mainly divide the voltage level by a voltage division ratio to clamp the DC level between the capacitor C1 and the cathode 6, and at the same time, the cathode flowing from the collector side of the transistor Q5 to the capacitor C1. A signal proportional to the current is output via the resistor R15.

Reference numeral 9 is a cathode current detection circuit, which includes three resistors R17 to R19, a capacitor C3, and an NPN.
Signal of a cathode current output from the black level clamp circuit 8 via the resistor R15 is smoothed by the resistor R17 and the capacitor C3 and input to the base of the transistor Q7. A voltage proportional to the cathode current is output from the collector of the transistor Q7 and input to the high voltage control circuit 4.

With such a configuration, the cathode current amount (anode current amount) is detected by the cathode current detection circuit 9, and the high voltage applied to the anode 2 is controlled by the high voltage control circuit 4 in response to this variation. , Stabilized.

[0010]

In the high voltage control method (1), the high voltage itself applied to the anode 2 of the CRT 1 is detected, and the high voltage control circuit 4 performs feedback control based on the detection result. Therefore, the high pressure can be stabilized with high accuracy. However, since it is necessary to secure a dynamic range of high voltage control with respect to variations in high voltage applied to the anode 2 that occurs for each product, a semi-fixed resistor R6 connected to the non-inverting input terminal of the operational amplifier A1 is provided for each product. The operating point must be adjusted. Further, the high voltage detection circuit 5 must be directly connected to a high voltage, and therefore must have high insulation properties, resulting in high cost.

Further, in the high voltage control method of the above (2), since the high voltage can be controlled purely in accordance with the fluctuation of the cathode current amount (anode current amount), the high voltage control method of the above (1) is required. There is no need to adjust the operating point. However, in order to detect the cathode current, the cathode 6
The drive circuit 7 for driving the
It is necessary to detect the current flowing through the capacitor C1 by the AC coupling by the black level clamp circuit 8. Therefore, for example, in a monochrome display, since the capacitor C1 and the black level clamp circuit 8 are essentially unnecessary, the product cost becomes high,
Further, the AC coupling by the capacitor C1 easily causes a sag (trailing phenomenon) in an image. Further, due to the function of the video circuit, there is a problem that the high voltage control method (2) cannot be applied when the cathode drive circuit needs to be DC-coupled to the cathode of the CRT.

Therefore, an object of the present invention is to solve the above problems and to provide a high voltage stabilizing circuit for a CRT (1) without being affected by variations in high voltage between products and dynamic range, and (2) semi-fixed. No adjustment by resistance is required,
(3) There is no need for an AC coupling circuit or a black-level clamp circuit between the cathode drive circuit and the cathode, and (4) an inexpensive implementation.

[0013]

In order to achieve the above object, the present invention provides a drive circuit for generating a voltage amplitude for driving a cathode of a CRT in response to a video signal, and a voltage proportional to the voltage amplitude of the cathode. Output means for detecting and generating an output voltage from which the high frequency component of the video signal has been removed; and means for controlling the voltage applied to the anode of the CRT in response to the output voltage from the output means. Characterize.

[0014]

According to the present invention, the voltage amplitude of the cathode of the CRT is detected, and the voltage applied to the anode of the CRT is controlled in response to the detection result.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In FIG. 1, 1 is a CRT, 2 is an anode of CRT 1, and 6
Similarly, 4 is a high voltage control circuit, 7 is a cathode drive circuit, and 10 is a cathode voltage amplitude detection circuit.

The connection between the emitters of the two transistors Q3 and Q4 in the cathode drive circuit 7 and the cathode 6 are DC-coupled via a resistor R11.

The cathode voltage amplitude detection circuit 10 includes a resistor R
20 and R21 and a low-pass filter having a capacitor C4, a voltage proportional to the voltage amplitude of the cathode 6 is detected by the voltage dividing resistors R20 and R21, and a low frequency output voltage obtained by removing the high frequency component of the video signal is obtained. Occur. As a result, for example, as shown in FIG. 4d, the cathode voltage amplitude that changes at a high frequency in response to the video signal is converted into a voltage fluctuation at a low frequency in which the high frequency component of the video signal is removed, as shown in FIG. 4b. It This low frequency voltage variation further causes resistance R20 and NP
The voltage is input to the high voltage control circuit 4 via the emitter follower of the N-type transistor Q8. The high-voltage control circuit 4 level-shifts the detected voltage of the cathode voltage amplitude from the cathode voltage amplitude circuit 10 so that it falls within the optimum control range by the Zener diode D5, inverts and amplifies it by the transistor Q1, and then the secondary voltage of the flyback transformer 3. Controls the voltage at the high voltage end of the winding.

Here, the voltage at the high-voltage side end of the secondary winding of the flyback transformer 3 is a, and the cathode voltage amplitude detection circuit 1
When the detection output of 0, that is, the cathode voltage amplitude is b, and the control output of the high voltage control circuit 4, that is, the voltage at the low-voltage side end of the secondary winding of the flyback transformer 3, is c, these a, b, and c There is a relationship as shown in FIG. 4 between each level fluctuation. Therefore, by determining the inverting amplification factor of the transistor Q1 (that is, the ratio of the resistors R1 and R2 on the collector side and the emitter side, R1 / R2) so that the variation of a and the variation of c are canceled out. The fluctuation of the high voltage applied to the anode 2 can be suppressed. As described above, b fluctuates at a low frequency in which the high frequency component of the video signal is removed, and the response frequency of control by the high voltage control circuit 4 becomes low. Therefore, the high voltage of the CRT fluctuates at the frequency of the video signal and There is no problem such as flickering.

It should be noted that the cathode voltage amplitude amount and the cathode current amount are not in a linear proportional relationship due to the gamma characteristic of the CRT as shown in FIG. 5 (II), but as shown in FIG. 5 (I), in the first place. The relationship between the anode current amount (= cathode current amount) and the high-voltage output voltage value of the flyback transformer is not linear, but rather the high-voltage fluctuation tends to decrease as the anode current amount increases. Conventional method for controlling high pressure proportional to the amount (Fig. 2)
Rather, the present invention in which the high output voltage of the flyback transformer is controlled in proportion to the cathode voltage amplitude amount as shown in FIG. 5 (III) enables more accurate feedforward control.

[0021]

As described above, according to the present invention, it is possible to stabilize the high voltage of the CRT with extremely high accuracy without requiring an extra circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

FIG. 3 is a circuit diagram of another conventional example.

FIG. 4 is a diagram showing a concept of voltage waveforms of respective parts in the embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between various voltages for a CRT.

[Explanation of symbols]

 1 CRT 2 Anode 3 Flyback Transformer 4 High Voltage Control Circuit 7 Cathode Drive Circuit 10 Cathode Voltage Amplitude Detection Circuit 14 Capacitor

Front Page Continuation (72) Inventor Masahiro Naito 1623 Shimotsuruma, Yamato City, Kanagawa 14 Japan ABM Co., Ltd. Yamato Works

Claims (1)

[Claims] 1. A drive circuit for generating a voltage amplitude for driving a cathode of a CRT in response to a video signal, and an output voltage obtained by detecting a voltage proportional to the voltage amplitude of the cathode and removing a high frequency component of the video signal. A high voltage stabilizing circuit in a CRT display device, comprising: output means for generating a voltage; and means for controlling a voltage applied to the anode of the CRT in response to an output voltage from the output means.