Output Circuit And Protection Circuit - Dell 2209WA Service Manual

Service Manual
pin VSEN_POL(pin12) is greater than approximately 1.5V, the PWM dimming
polarity will be negative. A voltage range of approximately 0.1V to greater than
1.5V to PDIM(pin11) results in minimum and maximum brightness
respectively.
The striking and operating frequency is determined by the external resistor
(R16) and capacitor( C1) connected to Pin8(CT).
LX1, HDR1 and LX2, HDR2 of U1 are used to drive Q1, Q2 and Q3,Q4 .
LX1, HDR1 and LX2, HDR2 are controlled by build-in PWM IC. Q1, Q 2 and
Q3, Q4 are switches that everyone has a build-in IGBTs.
ISEN( pin13)
For lamp "ON" detection, if the peak voltage at ISEN(pin13) is less than
approximately 0.8*ADJ and the voltage at VSEN_POL(pin12) is greater than
the preset voltage at OVPT(pin16), this indicates the lamp has not been
ignited.
During soft-start (lamp striking mode), if the voltage at ISEN(pin13) is
greater than approximately 0.8*ADJ and the voltage at VSEN_POL(pin12) is
less than the preset voltage at OVPT(pin16), this indicates lamp "ON"
condition. The striking period will end and the IC will switch to the normal
operation mode.
Once the IC switches to the normal operation mode, ISEN becomes(pin13)
the feedback signal input pin for the current regulation loop.
ADIM(pin18) Reference voltage for analog dimming
The ADIM is used to deal with the signal of DCR from IF BD. U1 can
adjust the CCFL current automatically based on the DCR signal.
Clamped between 0.52V and 2.45V, ADIM is passed into OZ9926A as
ADJ.
ADJ is the positive input signal to the internal OTA used for current
regulation. Thus, ADJ controls the lamp current amplitude. ADJ also set one of
the lamp "ON" condition, Which is 0.8*ADJ.
2.1.2)Output Circuit and Protection Circuit:(fig.3)
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