Samsung MSYS 5200, Service Manual

Page: 45 / 210

Samsung Electronics 5-29
Circuit Description
5-5 SMPS (Switching Mode Power Supply)
5-5-1 AC Input Stage
AC Input power path is the Fuse(F201) for A C
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 2’nd noise
filter(L202), and the thermistor(TH201). When
power is turned on, TH201 limits Power-On-Inlush-
Current by it’s high resistance, and when it’s
temperature rise, it’s resistance become about zero
ohm.
5-5-2 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.
5-5-3 Fuser Drive
Fuser is drived 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, i t
controls temperature by PID method.