Power Circuit - Samsung SF-4500 Service Manual

6-4-2-2. OUTPUT CONDITIONS
NO
1 RATED OUTPUT VOLTAGE
2 RATED OUTPUT CURRENT
3 MAXIMUM LOAD CURRENT
4 LOAD CHANGE RANGE

6-4-3. Power Circuit

6-4-3-1 INPUT
This product is equipped with a three-wire
grounding-type power inlet. Insulation is class 1.
When a power device part breaks down or some
trouble in this circuit causes a short, excess current
runs through a fuse and blows it to protect power
devices and the system from excess current and
prevent a fire.
Input filter of power input terminal removes line
noise flown in from outside and reduces noise which
is made in power circuit and logic part and conduct-
ed or radiated through power cords.
AC input voltage is rectified by bridge diode of full
wave rectifier, is converted to DC voltage by smooth-
ing circuit, and switches the power device of this
voltage.
As switching is in RCC(Ringing Choke Converter)
mode, switching frequency changes from about
50KHz to 100KHz.
PWM(Pulse Width Modulation) Control Circuit
adjusts the duty of the switching device by sensing
the change of output voltage, and protects this
product from excess current by receiving signals
from excess current detecting circuit.
Samsung Electronics
ITEM CH1
+5.0V
0.5A
0.8A
0.1 ~ 0.8A 0.03 ~ 1.3A
6-4-3-2 DRIVING CIRCUIT (START-UP CIRCUIT)
If you insert a power plug into AC outlet, full-wave
rectified DC output voltage is generated at input
electrolysis condenser and supplied to the gate of a
switching device through driving resistance. This
voltage drives the switching device. Once it is
driven, it continues to switch via PWM control
circuit with power supplied by auxiliary coil Nb.
6-4-3-3 SWITCHING CIRCUIT
(VOLTAGE STABILIZATION)
11.75V of 2nd voltage is detected by voltage detector
and feeds back through photo coupler to 1st PWM
Control Circuit signals compared by error amplifier.
PWM Control Circuit controls the gate of power tran-
sistor according to the feedback voltage so as to sup-
ply load with stable output voltage.
CH2
+11.75V
0.8A
1.3A
0.05 ~ 0.76A
CH3
+30V
0.5A
0.76A
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