Service manual

Circuit Description

3-38

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

AC Power Live

C18

R23

R24

R66

Logic Unit

Fuser On

SMPS Unit

DC Power

PC3

SY1

CON502

Zero crossing circuit