KR970002990B1 - Circuit for automatically limiting luminance - Google Patents

Abstract

An automatic luminance restriction circuit using the potential difference between the cathod and first grid electrode includes a detector 22 for commonly connecting a controller 21 to the cathod to detect whether the luminance is normal or not, an amplifier 23 for amplifying the waveform of the detected signal and sending it to the controller and first grid, and controller 21 for controlling the luminance using the amplified waveform. The controller is constructed to allow the cathod voltage to increase, decreasing the luminance. With the first grid electrode, the controller controls the grid voltage to be reduced, lowering the luminance. By doing so, the automatic luminance restriction circuit decreases the luminance to prevent transistors for horizontal output from being destructed.`

Description

Automatic Luminance Limiting Circuit Using Transition Difference Between Cathode and First Grid Electrode

1 is a block diagram of a conventional automatic luminance circuit,

2 is an embodiment block diagram of the present invention;

3 shows the relationship between anode current and brightness,

4 is a relationship between the cathode and the first grid potential difference and the luminance,

5 is a luminance detection and amplification unit,

6 is an example of controlling an image amplification circuit;

7 is an automatic luminance limiting circuit by cathode control.

* Explanation of symbols for main parts of the drawings

21 control unit 22 detection unit

23: amplifier 31: balance operation unit

32: operating point adjustment unit 33: differential amplifier

34 filter 41 phase inversion

42: video preamplifier 43: video amplifier

The present invention relates to a circuit configuration that prevents a large anode current from flowing through the CRT when the luminance is extremely high and a high voltage circuit is overloaded to destroy a transistor for horizontal output. In particular, in the CRT display device, between a cathode voltage and a first grid. It is an automatic luminance limiting circuit using a potential difference between a cathode and a first grid electrode, which detects and controls an anode current by using a voltage difference, and detects and controls the image directly in an active manner when an extreme luminance rises.

1 is a conventional automatic luminance circuit limiting circuit, comprising: a high voltage circuit and a horizontal output circuit 11 connected to the anode overcurrent detector 12; An anode overcurrent detector 12 which detects the anode current and is connected to the detection waveform amplifier 13; A detection waveform amplifier 13 for detecting the detection waveform and sending a signal to the image amplifier and the first grid; An image amplifier 14 for sending the detected waveform to an image amplifier circuit; It consists of a line 13 'for controlling the luminance by sending the detected waveform to the first grid electrode.

The conventional circuit configured as described above controls the extreme brightness of the cathode or the first grid electrode by detecting the extreme overcurrent of the anode in the high voltage circuit or the horizontal output circuit.

However, in order to construct a conventional automatic luminance limiting circuit, when the deflection circuit board, the CRT driving circuit, and the image output circuit board are separated, it is inconvenient to connect these boards, and even if the deflection section and the image section are on the same board, the pattern is long. The result is very inconvenient and large substrate size.

Accordingly, in view of the related art, the circuit is configured to detect a voltage difference between the cathode and the first grid and apply it to the final image amplification output terminal or the grid electrode. That is, when the detection unit and the control unit are formed at the same place, the sensitivity is good and the control speed is high when the abnormal luminance phenomenon occurs.

2 shows an embodiment of the present invention.

The automatic luminance limiting circuit of the present invention includes: a detector 22 for detecting whether abnormal luminance is used to prevent the luminance from becoming extremely high; An amplifier 23 for amplifying the detected waveform; It consists of a control part 21 which controls brightness with this amplified waveform.

The circuit configured as described above detects and controls the anode current by using the voltage difference between the cathode voltage and the first grid on the direct image side when the luminance increases.

As shown in FIG. 3, the relationship between the anode current and the brightness increases as the anode current increases. In other words, the anode current and brightness are irreversible, and the relationship between the cathode and the first grid electrode and the brightness is inversely proportional to the brightness when the voltage difference is large and the brightness becomes dark, and when the voltage difference is small, the brightness becomes inversely proportional. You can see the relationship. If the voltage of the electrode of the first grid is connected to the ground, the voltage difference occurs only by the cathode voltage.

The present invention embodies the apparatus by focusing on the relationship between the two electrodes of FIG. In the circuit illustrated in FIG. 2, the detector is composed of the block diagram shown in FIG. The configuration of FIG. 5 includes a waveform manipulator 31 for manipulating a signal coming into the detector from the controller into an appropriate signal waveform for differential input; An operating point adjusting unit 32 for adjusting an appropriate operating point for the differential input with the first grid voltage; An automatic amplifier 33 which amplifies and outputs the difference by inputting the positive voltage thus obtained; It consists of a filter 34 which outputs only a predetermined frequency from the signal output from the differential amplifier and sends it to the image amplifier circuit or the first grid electrode.

FIG. 5 is a specific example of the differential amplifier circuit. The cathode voltage is input to the base side through the bias resistors R1 and R2, and the collector side is connected to the resistor R5 to which the voltage is applied and to the grounded resistor R5. The first grid voltage is input to the base side through the transistor Q1 composed of the emitter terminal, the rectifying diode D1, and the bias resistors R6 and R7, and the collector side is applied to the resistor R4 applying voltage. It is composed of a transistor Q2 connected to the connected and grounded resistor R5. The signal output from the collector side of the transistor Q1 and the grounded capacitor C1 are connected in common and connected to the image amplification circuit.

In the circuit configured as described above, due to the characteristics of the differential amplifier, the output voltage has a proportional voltage due to the difference between the cathode voltage and the grid voltage. Since there is a big difference between the cathode voltage and the grid voltage, the cathode voltage is divided by the grid voltage as a reference voltage and input to the differential amplifier circuit which is a detection unit.

When the voltage difference between the two electrodes has a very small value, that is, when the operating point of the auto luminance limiting circuit is reached, the amplification circuit output waveform becomes small. The detected output is sent to the controller, which includes a method of controlling the voltage of the cathode and a method of controlling the grid. In order to control the cathode, when the cathode voltage is high, the brightness is lowered, and when the cathode voltage is low, the brightness is high.In order to darken the brightness, the controller is configured in the direction of increasing the cathode voltage.In the latter case, the voltage of the first grid electrode is opposite to the former. The higher the luminance, the higher the grid voltage, and the lower the luminance, the lower the grid voltage.

FIG. 7 shows an example of forcibly increasing the voltage of the image amplifier circuit by controlling the cathode, and includes: a phase inversion unit 41 for phase inverting the differential amplifier output signal of FIG. 5; An image preamplifier 42 for amplifying a minute input; The image amplifier 43 is configured to output an image signal for controlling the cathode to the cathode of the CRT according to the signal output from the phase inversion unit 41 and the signal generated from the image preamplifier 42.

The circuit configured as described above is configured to forcibly increase the voltage of the image amplifier circuit to increase the cathode voltage in order to lower the luminance when the luminance is higher than necessary.

When adopting the self-odor limiting circuit proposed in the present invention, a connector, a wire, etc. for connecting between substrates in the conventional method, which detects an anode current to a high voltage or deflection circuit and sends it to an image amplifier circuit, controls the image amplifier circuit. It is economically advantageous because it eliminates the necessity, and fortunately, even if it is on one substrate, the pattern on the substrate is elongated to compensate for the disadvantage of increasing PCB. Active control also improves the reliability of the automatic luminance limiting circuit in terms of sensitivity.

Claims (4)

A detector 22 which connects the control unit 21 and the cathode to detect abnormal luminance; An amplifier 23 which amplifies the detected waveform and sends a signal to the controller and the first grid; And a control unit (21) for controlling the luminance with the amplified waveform. The method of claim 1, wherein the detection unit 22 is connected to the resistor (R5) and the ground connected to the resistor (R3) for applying the voltage to the base side and the collector side is applied to the voltage via the bias resistor (R1, R2) The first grid voltage is input to the base side through the transistor Q1 composed of the emitter terminal, the rectifier diode D1, and the bias resistors R6 and R7, and the collector side applies the voltage to the resistor R4. A differential amplifier 50 having a transistor Q2 coupled to a grounded resistor R5 connected to the grounded resistor R5 and having a common output connected to a signal amplified by the collector side of the transistor Q1 and a grounded capacitor C1 connected to an image amplifier circuit. Automatic luminance limitation circuit using the potential difference between the cathode and the first grid electrode, characterized in that consisting of. 2. The apparatus of claim 1, wherein the amplifying section (23) comprises: a waveform manipulation section (31) for manipulating a signal coming from the control section (21) into the detecting section (22) to a suitable signal waveform suitable for a differential input; An operating point adjusting unit 32 for adjusting an appropriate operating point for the differential input with the first grid voltage; A differential amplifier 33 which inputs the positive voltage thus obtained and amplifies the difference; An automatic luminance limiting circuit using a potential difference between a cathode and a first grid electrode, characterized by comprising a filter 34 outputting only a predetermined frequency from a signal output from the differential amplifier to an image amplifier circuit or a first grid electrode. 2. The circuit arrangement according to claim 1, wherein the circuit arrangement for forcibly increasing the voltage of the image amplifying circuit to control the cathode comprises: a phase inverting portion (41) for phase inverting the differential amplifying output signal; An image preamplifier 42 for amplifying a minute input; The cathode and the first grid electrode, characterized in that composed of an image amplifier 43 for outputting the image signal for controlling the cathode to the cathode of the cathode ray tube according to the signal output from the phase inversion unit and the signal output from the image preamplifier Automatic luminance limiting circuit using potential difference between them.