Samsung SCX-5315F Service Manual page 158

Circuit Description
3-8-2 AC Input Stage
AC Input power path is consist of the Fuse (F1) for AC current limit, the Varistor (TNR1) for by-passing high
Voltage Surge, the discharge resistor(R1), the AC Impalse Noise Filtering Circuit (C2, C4, LF1), the Common
Mode Grounding Circuit (C5, C6), the 2'nd noise filter (C7, LF2), and the thermistor (TH1).
Wher power is turned on, TH 1 limits Inlush-Current by it's high resistanle, and When it's temperature rise, it's
resistance become about Zero ohm.
3-8-3 SMC(Switched Mode Control)
The AC input voltage is rectified and filtered by BD1 and C10 to create the DC high voltage applied to the pri-
mary winding of T1, Q5 pin #1 is driven by the SMPS device IC2, IC2. auto-starts and chops the DC voltage.
The U502 is PWM SMPS IC and has internally a SMC(switched mode control) IC and a MOSFET output
stage. The SMC IC has a Auto-restart without a Power Supply for the IC and a Thermal Shutdown function
and so on. R4, R5, C11, D1 clamp leading-edge voltage spikes caused by transformer leakage inductance.
The power secondary winding(Pin #5~6)is rectified and filtered by D8, D9, L2, C33, C34 to create the 5V out-
put voltage. The bias winding(Pin #9~8)is rectified and filltered by D2 and C12 to create U502 bias voltage.
The secondary output 5V is regulated through the path of the voltage divide by R34, R35.
3-8-4. Fixed Temperature Control
3-8-4-1. Fixed Lamp Control Circuit
AC Neutral
CON502
3-38
R24
C18
SY1
R23
<Fixed Lamp Control Circuit>
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AC Power Live
L1
Zero crossing circuit
4
2
R66
1
6
PC3
Samsung Electronics
Logic Unit
Fuser On
SMPS Unit
DC Power