Commodore 1940 - Page 36

8.
Power Supply Circuit
The power supply circuit consist of SMPS and chopper.
Variations
in
AC input voltage
and
load control the operating frequency and duty cycle.
SMPS
is
much more favorable than the series regulator for the higher efficiency
in
the aspects of the thermal
dissipation by the power loss
in
itself, the wide regulation range, the simple construction and the light weight. This
power supply can handle the wide input voltage variation from 90V
to
137V
AC
for UUCSA models and from 180V
to 265V AC for world trade models.
6
......
--j(
TR3
__
---+-
..... -
__
-+--1.
TR2
02
<Fig
16.
Internal Equivalent Circuit of STK 73410
ll:
>
TR3
of
IC001
functions as a switch and while
on,
stores energy
in
the winding 1-3 of T001.
The stored energy
is
taken from the output winding 1-3 of
T001
while TR3
is
off. The output voltage is rectified by
0031,
0036
and
0037
for main B+, 78Vdc, 24Vdc.
The output voltage
is
kept constant by balance between the energy supplied to the Winding 1-3 (which is
controlled by on-time of TR3)
and
that taken from the 5-6.
1) When the power switch is turned
on,
the AC input voltage rectified
and
smoothed by 0001,
CO
10 and supplied
to the terminal 3 of T001. The starting current flows to TR3 to turn it
on.
2) when TR3
is
turned on, the start pulses are induced
to
the coils of 7-5, allowing the collector current to
increase the base current.
3)
Current also flows through the winding 5-6. The voltage rectified by
01
is
applied to the base of TR1, thereby
turning off the TR1, arid also turning off TR2 and TR3.
4) The output current flows into the secondary winding of
T001
while TR3
is
being kept off.
5)
The kick pulse
of
output current from the secondary, winding
is
induced into the winding 7-5, thus turning on
TR3 once again.
33