Smps (Switching Mode Power Supply); Ac Input Stage; Smc (Switched Mode Control); Fuser Drive - Xerox WorkCentre 385 Service Manual

Table of Contents

SMPS (Switching Mode Power

Supply)

AC Input Stage

AC Input power path is the Fuse(F201) for AC

current limit, the Varistor(TNR201) for by-passing

high voltage surge, the discharge resistor(R201),

the AC Impulse Noise Filtering Circuit(C201/L201/

C202),

the

Common

Mode

Circuit(C203/C204), the 2nd noise filter(L202), and

the thermistor(TH201). When power is turned on,

TH201 limits Power-On-In Rush-Current by it's

high resistance, and when its temperature rise, its

resistance becomes approximately zero ohms.

SMC (Switched Mode Control)

The AC input voltage is rectified and filtered by

DB201 and C207 to create the DC high voltage

applied to the primary winding of T201. T201 pin

#1 is driven by the SMPS device TOP226(U201).

U201 auto-starts and chops the DC voltage. The

U201 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. C208/R208/D202 clamp

leading-

edge

voltage

spikes

transformer leakage

inductance. The

secondary winding (pin #11-12) is rectified and

filtered by D252,C251,L251, and C255, C259 to

create the 5V output voltage. The bias winding (pin

#4-5) is rectified and filtered by D203 and C213 to

create U201 bias voltage. The secondary output

5V is regulated through the path of the voltage

divide by R253/R254 - U251 switching - PC252 -

the bias voltage of U201 - U201 PWM duty cycle -

T201 secondary voltage. C209 filters internal pin,

determines

the

auto-restart

frequency,

together with R251 and R210, compensates the

control loop. Q251 of the secondary stage 24V is

the Low Power-loss Regulator with built-in

overcurrent protection function and overheat

protection function, and consists a control IC and a