41
which composed of 4 build-in diodes, it inverts AC to DC.
1.3.1.2 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 Vcc pin during start-up, the MOSFET Q804 is initially
off, and the Vcc pin capacitor is charged. When the Vcc pin voltage reaches approximately 10V, 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 CS 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.
D804 and C807 to provide internal Auxiliary voltage to Vcc pin during normal operation.
Otherwise, error amplifier and feedback current input the CS pin for duty cycle control.
1.3.1.3 DC_5V and DC_14V 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 14V, 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.
1.3.1.4 Feedback and OVP Protect Circuit
Pin R of IC803 is supplied 2.5-v stable voltage. It connects to 5V and 14V 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 14V not be
increased.
I/F Board Circuit
1.3.2.1 RGB CAPTURE
- Signal RED,GREEN,BLUE input through CN103 #1,#2,#3, Stop DC via C123, C124 and C125,
and then enter into U104 (scaler) analog input terminal #16,#14,#12, and then scaler deals with
signal internally. EP102, EP103 EP104 are ESD protector to prevent U104 from ESD.
- Signal DDC_SCL (series clock) inputs via CN103#15, and then passes through EP109 for ESD
protection, goes into U102 (MCU) #5.
- Signal DDC_SDA (series data) inputs via CN103#12, and then passes through EP108 for ESD
protection, goes into U102 (MCU) #8.
- Signal TTL vertical sync. (Vsync) inputs via CN103 #14, and then clamped by EP107, passes
through R162, and then goes into IC U104 (scaler) #8.
- Signal TTL horizontal sync. (Hsync) inputs via CN103 #13, and then clamped by EP106, passes
through FB104, R163, and then goes into IC U104 (scaler) #9.
- CN103#5 is defined as cable detect pin, this detector realize passes through D101, D102, Q105
or through D101, D102, Q105, R107,Q106 change to MCU_VCC.
- U103 power is supplied by MCU_VCC.
- U103 is an EEPROM IC which is memory and EDID data saved in it.
1.3.2.2 Buttons Control
- Button “Power” on right side bezel connects to U102 (MCU) #9 through R134, via CN901#1.
- Button “E-Color” “AUTO”“MENU” “UP” “DOWN “on right side bezel connects to U102 (MCU)
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