Power Board Operation Theory; Inverter Circuit - HP WF1907 Service Manual

2. Inverter Circuit

This unit operates on an output voltage of 22V from power source.
2.1 VDD: R105 get a +5VDC for I101 power supply.
2.2 Control IC: I101 (OZ9938)
2.2.1 Enable : When pin 1 of I101 is over 2V, I101 works. If it is under 1V, I101 turns off.
2.2.2 OSC: When I101 enabled, C104/R118/R107 (pin 13 of I101) determine the operating
frequency.
2.2.3 SST: C106 (pin 12 of I101) provides soft start function.
2.2.4 Ignition: IC provides higher operating frequency internally for more striking voltage until
regulation of feedback of lamp current. And provide 2 sec striking time.
2.2.5 Dimming control: The external PWM voltage of R136/C111 control the duty pulse of
burst-mode to drive and perform a wide dimming control for the CCFL. The burst-mode
frequency is determined by scalor IC.
2.2.6 Regulation: Pin 5 of I101 provide regulation of the CCFL current from feedback. The
non-inverting reference is at 1.25V nominal.
2.2.7 Protection: Open-lamp protection in the ignition period is provided through pin 6 of I101.
Removal of the CCFL during normal operation will trigger IC to turns on and shuts off the
inverter. This is latch function.
2.2.8 Output drivers: The configuration prevents any shoot-through issue associated with
bridge-type power conversion applications. Adjusting the overlap conduction between
Q104, Q105, the CCFL current regulation is achieved.
2.3 Half-bridge switching/Transformer: Q104, Q105, C122, C123, C134 compose half-bridge
switching to convert DC into AC for driver the CCFL.
2.4 Detection: C112, C114, C115, C116, C118, C119, R126, R116, R115, R117, R119, R121, R122, R125
detect the output voltage and ensure a rated voltage by pin 6 of I101 ensure not a open-lamp.
2.5 Feedback: D116, D117, D120, D121, R111, R130 sense the lamp current for negative feedback
and regulation.
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