BenQ M2700HD, Service Manual, Page: 46 / 53

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Vcc pin capacitor is charged. When the Vcc pin voltage reaches approximately 16.5V, the control circuitry
is activated and the soft-start begins. The soft-start circuit gradually increases the duty cycle of the
MOSFET from zero to the maximum value over approximately 5ms. a stably output voltage Will be
increase about 20ms later, and then feedback a continue current through the IC803 which control the
output of the PWM IC. If no external feedback/supply current is feed into the FB pin by the end of the
soft-start, the current Set point will be above the fault level, FAULT flag is raised, if the FAULT duration
exceeds 56ms, the output controller disable,
Resistor R845, R846, R849, R52, are for line over voltage shutdown(OVP) and Brown Out Protection
(BOP)
When PWM is turned off, the main current flow will be consumed through R803,R804,ZD801, C808
and D802, This will prevent MOSFET Q803 from being damaged under large current impulse and voltage
spike.
D813 and C823 to provide internal Auxiliary voltage to Vcc pin during normal operation.
DC_5V and DC_16V Output Circuit
For DC VCC 5V, D817,D810 is used to rectify the inducted current. R809 and C816, are used to
store energy when current is reversed. The parts including C819, C820,C821,C842,C843,C827 and
c817 are used to smooth the current waves.
For DC Audio 17V, D805 is used to rectify the inducted current. R812 and C813, are used to store
energy when current is reversed. The parts including C823, C824,L803 are used to smooth the
current waves.
For DC 30V, D804,D806,D807 is used to rectify the inducted current. R817 and C828 are used to
store energy when current is reversed. The parts including C844 is used to smooth the current waves.
Feedback Circuit
Pin R of IC803 is supplied 2.5-v stable voltage. It connects to 5V and 17V output through R833,
R829,R827 and R830, they are output voltage sampling resistor. When the sampling voltage more
than 2.5V or less than 2.5V, current of FB IC802 will change, this can change the voltage from T801.
5.6 I/F Circuit
5.6.1.1 RGB CAPTURE
- Signal RED,GREEN,BLUE input through CN102 #1,#2,#3, Stop DC via R145&C125,
R147&C126 and R149&C127 and then enter into U111 (scaler) analog input terminal
#36,#34,#31, and then scaler deals with signal internally.
- Signal DDC_SCL (series clock) inputs via CN102#15, and then passes through R167, goes into
U111#67.
- Signal DDC_SDA (series data) inputs via CN102#12, and then passes through R168, goes into
U111 #66.
- Signal TTL vertical sync. (Vsync) inputs via CN102 #14, and then clamped by ZD104 Zener,
passes through R170, and then goes into IC U111 (scaler) #30.