Acer AL1702 AL1702 Service Guide - Page 6

AL1702 2. InverterOperation This unit operates on an output voltage of 22V from power source. 2.1 VCC: When On/Off pin of P802 is high level input, Q106 turns on and provides +5VDC for I101 power supply. 2.2 Control IC: I101 (OZ960S) 2.2.1 Enable : When pin 3 of I101 is over 1.5V, I101 works. If it is under 1.5V, I101 turns off. 2.2.2 OSC: When I101 enabled, R108/C115 (pin 17/pin18 of I101) determine the operating frequency. 2.2.3 SST: C104 (pin 4 of I101) provides soft start function. 2.2.4 Ignition: R109 (pin 8 of I101) provides higher operating frequency for more striking voltage until regula- tion of feedback of lamp current. C103 (pin 1 of I101) determine the striking time. 2.2.5 Dimming control: The divided voltage of R106/R105/R104 control the duty pulse of burst-mode to drive Q105 and perform a wide dimming control for the CCFL. The burst-mode frequency is determined by C116. 2.2.6 Regulation: Pin 9/pin 10 of I101 provide regulation of the CCFL current from feedback. The non-inverting reference (pin 10 of I101) is at 1.25V nominal. 2.3 Protection: Open-lamp protection in the ignition period is provided through both pin1 and pin 2 of I101 to ensure a rated voltage is achieved and a required timing is satisfied. Removal of the CCFL during normal operation will trigger the current amplifier (pin 9/pin 10 of I101) output and shuts off the inverter. This is latch function. 2.4 2.4.1 Output drivers: The configuration prevents any shoot-through issue associated with bridge-type power conversion applications. Adjusting the overlap conduction between I102 P-MOSFET and I103 N-MOSFET, I101 N-MOSFET and I103 P-MOSFET, the CCFL current regulation is achieved. 2.4.2 Full-bridge switching/Transformer: I102/I103 /C123/T101 compose full-bridge switching to convert DC into AC for driver the CCFL. 2.5 Detection: C128/C129/C132/D115/D114/C118 detect the output voltage and ensure a rated voltage by pin2 of I101. 2.6 Feedback: D116/D117/R120/D108/R116 sense the lamp current for negative feedback and regulation. The divided voltage on R116 will be at 1.25V. Inverter Circuit Block Diagram VCC ON / OFF Brightness control Regulator U.V.P. VDD Control IC : OZ960 Enable OSC SST Dimming control Output driver Protection Ignition Regulation Full-bridge switching Transformer Detection Feed back Lamp Page 4