SERVICE MANUAL
Document No
Date of Origin
Date of REV
51-L-DSR004
98-10-21
PAGE REV.
0
PAGE
29 /102
S-00-005(96.03.27)
REV.1
7-4. SMPS
7-4-1.
The SMPS's Fundamental Operation
The present
circuit
uses the commercial
power supply of AC230V.
The power is
supplied
at the F1 Live part and Neutral
part when the AC power is On. During
this operation,
the TH1 THERMISTOR
protects
the semiconductor
devices
from a
sudden current
and the TNR1 Varistor
protects
the semiconductor
devices
setted
behind the Fuse of the AC Suge Voltage
(> AC 380V).
Capacitors
C1,C2, and inductor
L1 are Filter circuit
which eliminate
the noise
introduced
from a AC Line and the noise, originated
from an internal
circuit,
flowing
to AC Line.
The voltage,
passed through
the Filter circuit,
is rectified
by DC Diode (D1 -
D4) and after this wave is smoothed
by a capacitor
C3 and finally
it is supplied
to Q1's DRAIN through
the Primary
Trans.
The rectified
voltage
is changed
to around DC 310V calculated
by the equation
V=
¡î
2 V and it is called Vin. Also, when the Vcc power is supplied
to Q1 SMART IC
through
R2, Q1 SMART IC internal
circuit
works and supplies
GATE Signal of 50KHz
to the GATE of Q1 SMART IC.
The Dnn voltage
of Q1 is by passed to Ground when Q1 SMART IC is turned on.
In this process,
the FEEDBACK
PIN of SMART IC serves as a function
to regulate
voltage
level and to protect
from an excessive
load simultaneously.
The method used for the voltage
regulation
is Current
Mode Control
method which
modulate
the width of PWM DUTY comparing
the error voltage
detected
by PHOTO
COUPLER
and the value of MOSFET DRAIN Current
detected
by current
detection
resistor.
In the process,
it also occurs an inverse
power at Secondary
trans.
This kind of circuit
is PWM type and this cycle is realized
continuously.
The working
frequency
is fixed at 50kHz. The working
switching
pulse is taken to
the Secondary
trans where it absorves
the energy by resonating
the frequency
oscillation
with L and C of Secondary
Trans (F=1/2
¥ð ¡î
L C).
This energy is rectified
by Diode and it is smoothed
by a capacitor
and finally