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OZ9910

Dual Forward PWM Controller

O2Micro International 

9. Feed-forward Compensation

Input voltage to the IC is intelligently processed to

yield a constant/symmetrical waveform at

CMP_SST (pin 10) to achieve a feed-forward-

compensation function during dimming control.

10. Output Drives

The four output drives are designed to turn-on and

turn-off four switches M1, M2, M3 and M4 with

intelligent phase-shift control technique. The

design allows the free-wheeling diode to reset

transformer in each half cycle. The body diodes

associated with four switches can be served as

the free-wheeling diodes. For example, the diode

D3 and diode D4 are used as free-wheeling

diodes for M1 and M2 switches during the first half

cycle. The diodes D1 and D2 are used as the

free-wheeling diodes for M3 and M4 switches

during the next half cycle. The switches in the

bridge are configured such that M1/M4 and

M2/M3 are turned-on complementarily. This

brake before make (BBM) is implemented to

prevent the power source shorted to the ground.

Adjusting the overlapped conduction between

switches M1/M2 and M3/M4 senses the current

flowing in the CCFL, thus the power delivered to

the CCFL is regulated.

The waveforms associated with a typical

two-transistor forward converter are shown in

Figure 4, page 12.

OZ9910

CONFIDENTIAL

OZ9910-DS-1.0

Page 9

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