Service manual

Page 4
AL1702
2.Inverter Operation
This unit operates on an output voltage of 22V from power source.
2.1VCC: When On/Off pin of P802 is high level input, Q106 turns on and provides +5VDC for I101 power supply.
2.2Control IC: I101 (OZ960S)
2.2.1Enable : When pin 3 of I101 is over 1.5V, I101 works. If it is under 1.5V, I101 turns off.
2.2.2OSC: When I101 enabled, R108/C115 (pin 17/pin18 of I101) determine the operating frequency.
2.2.3SST: C104 (pin 4 of I101) provides soft start function.
2.2.4Ignition: 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.
2.2.5Dimming 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.
2.2.6Regulation: 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.
2.3Protection: 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
2.4.1Output 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.
2.4.2Full-bridge switching/Transformer: I102/I103 /C123/T101 compose full-bridge switching to convert DC
into AC for driver the CCFL.
2.5Detection: C128/C129/C132/D115/D114/C118 detect the output voltage and ensure a rated voltage by pin2 of
I101.
2.6Feedback: 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
Regulator
U.V.P. Enable
OSC
SST
Dimming
control
Output driver
Protection
Ignition
Regulation
Control IC : OZ960
ON / OFF
Full-bridge switching
Transformer
Lamp
Feed back
Detection
Brightness
control
VDD