Xerox WorkCentre 385, Service Manual

Page: 178 / 184

WorkCentre 385
SMPS (Switching Mode Power Supply)
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7 - 44
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 Grounding
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 caused by
transformer leakage inductance. The power
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, and
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
drive transistor. It switches the input DC voltage
and the switched DC voltage is filtered by C257.
D204 and D205 clamp impulse noises.
Fuser Drive
Fuser is driven by the Triac(Q201) that AC input
power is applied directly and the Photo-
triac(PC251) that is controlled by Engine
controller. The Thermistor resistance changes
according to Heat Roller in Fuser, the voltage in
temperature sensing circuit changes according to
this resistance change, and this feedbacks to
Engine Controller, it controls temperature by PID
method.
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