Acer AL2017 Service Manual page 7

Acer
initially off, and the Vcc pin capacitor is charged. When the Vcc pin voltage reaches approximately
14V, 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 4ms.
If no external feedback/supply current is fed into the FB pin by the end of the soft-start, the current
Setpoint will be above the fault level, FAULT flag is raised, if the FAULT duration exceeds 80ms,
the output controller disable resistor R808, R809, R810, R811 are for line over voltage
shutdown(OVP)
When PWM is turned off, the main current flow will be consumed through R804 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.
Otherwise, error amplifier and feedback current input the FB pin for duty cycle control.
1.1.3 DC_5V and DC_16V Output Circuit
For DC 5V, D805 is used to rectify the inducted current. R828 and C814 are used to store
energy when current is reversed. The parts including C818, C822, C820,L803 are used to smooth
the current waves.
For DC 16V, D803 is used to rectify the inducted current. R827 and C813 are used to store
energy when current is reversed. The parts including C815, C817 and L802 are used to smooth the
current waves.
1.1.4 Feedback and OVP Protect Circuit
Pin R of IC803 is supplied 2.5-v stable voltage. It connects to 5V and 16V output through
R822, R823 and R824. R822, R823 and R824 are output 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.
OVP Protect Circuit: When output is overvoltage, the auxiliary winding voltage will be
increased, when it reaches about 14V. Q803 is triggered . It makes the IC802 Pin 1 exceed 5V, then
the IC802 output will be disabled.
Q801, R816, R817 and ZD803 make up of dummy loading circuit. For start-up sequence,
during 5V output take place high loading first, this dummy loading circuit operated to insure 16V
not be increased.
1.2 Interface Board Circuit
1.2.1 RGB CAPTURE
- Signal RED,GREEN,BLUE input through CN103 #1,#2,#3, via R105,FB101, R101,R106,
FB102 ,R102, R107,FB103,R103, Stop DC via C101, C102 and C103, and then enter into U104
(TSUM56AWHK) analog input terminal #59,#56,#54, and then TSUM56AWHK deals with signal
internally. D101, D102, D103 are ESD protector to prevent U104 from ESD.
- Signal DDC_SCL (series clock) inputs via CN103#15, and then passes through ZD104 Zener for
ESD protection, via R121, goes into EDID EEPROM IC U102 #6.
- Signal DDC_SDA (series data) inputs via CN102 #12, and then passes through ZD105 Zener for
ESD protection, via R122, goes into EDID EEPROM IC U102 #5.
- Signal TTL vertical sync. (Vsync) inputs via CN103 #14, and then clamped by D103 Zener, passes
through R116, and then goes into IC U104 #64.
- Signal TTL horizontal sync. (Hsync) inputs via CN103 #13, and then clamped by D102 Zener, passes
through FB104,R115, and then goes into IC U104 #63.
- CN103#5 is defined as cable detect pin, this detector realize passes through R113 ,go into U104#26,
and ZD109 is ESD protector.
- U102 +5V is supplied by PC via CN103#9 with ZD101 for ESD protection, or supplied by Monitor
self via D104.
- U102 is an EEPROM IC which is memory and EDID data saved in it.
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Service Manual