Philips 170B LCD monitor inverter circuit

Philips 170B LCD monitor inverter circuit

The figure below shows the inverter circuit of Philips 170B LCD monitor . As can be seen from the figure, it is mainly composed of the inverter control chip Ul and the startup power supply circuit Ql and Q2. It is composed of switching circuits Q3 and Q4, high-voltage transformers and resonant circuits. It has 2 sets of high-voltage transformers to supply power to 4 backlight tubes.     DC 18 V supplies power to the inverter. The start/stop control signal (ON/OFF) is first added to the base of the 02 transistor. The start pair is high level, Q2 is turned on, and the collector voltage of Q2 decreases, so Ql (PNP type transistor) is also turned on, the +18 V power supply supplies power to the control chip UI @ pin through Q1, Ul starts, and the @ pin outputs a pulse signal to drive Q4, and Q4 provides a pulse signal for the gate of the field effect transistor Q3. In addition to providing a driving signal to the base of Q14, the D-pole output of Q3 is also added to the @ pin of the high-voltage transformer through the inductor Ll. The @ and @ pins are connected to the collectors of the two oscillation transistors. C16 is the resonant capacitor. The high-voltage transformer oscillates under the action of the driving signal. T1 is a step-up transformer, and the output peak value of the secondary @ and ⑦ pins can reach 700-800 V. This signal supplies power to both lamps simultaneously through the lamp holder.     When a problem occurs in this circuit, you can first check the output of the high-voltage transformer. As long as the oscilloscope probe is close to the core of the high-power transformer , the oscilloscope will sense a strong AC signal. If there is no signal, it means that the high-voltage transformer has no output. Then check whether the signal output of pin ⑦ and pin @ of the control chip is normal. There should be pulse signal output in normal working state. If there is output, check whether Q3, Q4, Q14, Q8 and the oscillation transistor are good. If there is no signal, check whether the +18V power supply and Ql, Q2 and other circuits are in good condition.