BenQ G2220HD - 21.5" LCD Monitor, Service Manual, Page: 39 / 47

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High Voltage to Low Voltage Control Circuit
C804 is used to smooth the wave from rectifier. IC802 is a highly integrated PWM controller. When
rectified DC high voltage is applied to the HV pin during start-up, the MOSFET Q804 is initially off, and the
Vcc pin capacitor is charged. When the Vcc pin voltage reaches approximately 16.0V.
When PWM is turned off, the main current flow will be consumed through R805,C806 and D802, This will
prevent MOSFET Q804 from being damaged under large current impulse and voltage spike.
D803 and C807 to provide internal Auxiliary voltage to Vcc pin during normal operation.
DC_5V and DC_24V Output Circuit
For DC VCC 5V, D807 is used to rectify the inducted current. R816 and C816 are used to store
energy when current is reversed. The parts including C819, C820, C822, L803, and C823 are used to
smooth the current waves.
For DC 24V, D805,D806 is used to rectify the inducted current. R827 and C815are used to store
energy when current is reversed. The parts including C817, C818, C830, C839, L802 is used to smooth
the current waves.
Feedback Circuit
Pin R of IC803 is supplied 2.5V stable voltage. It connects to 5V and 24V output through R822,
R825, R826 and There are output voltage sampling resistor. When the sampling voltage more than
2.5V or less than 2.5V, current of COMP IC802 will change, this can change the voltage from T801.
5.6.3. RGB CAPTURE
- Signal RED,GREEN,BLUE input through CN102 #1,#2,#3, Stop DC via R114&C113, R115&C114
and R116&C115 and then enter into U105 (scaler) analog input terminal #16,#14,#12, and then
scaler deals with signal internally.
- Signal DDC_SCL (series clock) inputs via CN102#15, and then passes through R131, goes into
U108#2.
- Signal DDC_SDA (series data) inputs via CN102#12, and then passes through R132, goes into
U108 #3
- Signal TTL vertical sync. (Vsync) inputs via CN102 #14, and then clamped by ZD105 Zener,
passes through R134, and then goes into IC U105 (scaler) #8.
- Signal TTL horizontal sync. (Hsync) inputs via CN102 #13, and then clamped by ZD104 Zener,
passes through FB101,R133, and then goes into IC U105 (scaler) #9
- CN102#5 is defined as cable detect pin, this detector realize passes through R125 Pull high, go
into U108#24.
5.6.4 Buttons Control
- Button “Power” in right of bezel connects to U108 #9 through R156, via CN104#8.
- Button “UP” “DOWN ““MENU” “ENTER” in the bottom of bezel connects to U108 #21,#22, through
R188,R189, via CN104 #3,#2
- U106 is an EEPROM IC which memory OSD setting and save the value adjusted by user.