Liquid crystal high-pressure board
Liquid crystal high-voltage panel, also known as LCD, is an important part of the LCD system, which is responsible for providing high enough input voltage to make the LCD light. It can be said that the high-voltage board is a controllable inverter circuit.
Circuit composition of liquid crystal high voltage board.
The circuit of LCD high voltage board consists of a pulse width generation IC (including peripheral circuits such as oscillation/control/feedback), power supply control circuit, self-excited oscillation generator, a feedback sampling circuit, etc.
Pulse width generation IC is mainly responsible for generating a rectangular pulse signal, which changes with the modulation of, to adjust the power supply size from 12V to self-excited oscillator, to generate different high voltage with different power supply, for the lamp to light. It is surrounded by an oscillating circuit, etc.
Generally, the power supply control circuit consists of several triodes. With the control voltage of the mainboard, the power supply of the pulse width IC is turned on or off, so as to control the whole booster board.
The self-excited oscillation generator mainly produces the high voltage required by the lamp. When the voltage is applied to it, the self-excited oscillation can be generated and the inverter high voltage (i.e. inverter) can be generated. The added voltage is 12V pulse width IC modulated (generally, the input is between 9-12v after modulation)
The feedback sampling circuit mainly collects the voltage and current of the self-excited output and the secondary (low-voltage line) of the lamp tube and feeds back to the pulse width IC to stabilize or cut off its pulse width output (the light we see in daily life is off, that is, the feedback circuit plays a role, resulting in no output of the pulse width.
Principle of liquid crystal high-pressure board
The circuit is mainly composed of drive circuit (oscillation circuit, modulation circuit), DC conversion circuit, Royer structure drive circuit, protection detection circuit, resonance capacitance, output current sampling, CCFL, etc. in the actual high-voltage board, the oscillator, modulator and protection circuit are often integrated together to form a small integrated circuit, Generally, it is called PWM control IC. The drive circuit adopts the Royer structure. The drive circuit of the Royer structure is also called a self-excited push-pull multivibrator, which is mainly composed of a power output tube and a step-up transformer. It can be used together with PWM control IC (such as tl1451, ba9741, bit3101, bit3102, etc.) to form a high-voltage board circuit with brightness adjustment and protection function. On / off is the input end of the oscillator start/stop control signal, which is from the MCU of the drive board (mainboard). When the LCD part or the circuit of the step-up board is connected to the same board (i.e. connected together), no output or abnormal power supply will also occur. During maintenance, the power supply of the step-up part can be cut off first to confirm the problem
This problem can be caused by an abnormal brightness control circuits, low 12V, low IC output, and abnormal high-voltage circuit on the brightness dimming booster board. Some of them may be accompanied by protection after heating for tens of seconds, resulting in no display.
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