Tandy 2000 Service Manual page 165

Tandy@
Model
2000
Service
l'lanual
voltages
may
easily
exceed
the
breakdown
rating of
the
switch
or the insulation of the inductor.
Block
Diagram
The
basic
circuit illustrated in
Figure
7-34 can be divided
into three functional blocks:
Input
DC
supply, Primary,
and
secondary. To
make
use of this modelr w€ need
to
expand
it
to provide control for the switch timing and to include
sufiicient circuitry to satisfy
performance and
reliability.
+I
2V
disk
+l-2V
LIl I
i nnrrf nar
rrrt/u L uv
supply
output
filters
soft start Iatch
output
filter
Control
IC
du
ti'
cy
c
I
e
con
trol
os
ci
I
Iator
current limit
output driver
reference with
scft start
output
f
i lter
f
eedback
isolat ion
load sens
+5v adj.
feedback
s
i gnal
compen sat ion
Figure
7
-34
Block
Diagram.
The
other blocks provide additional output voltages'
add
safety
or protective features,
reduce
circuit
noise,
and
develop
signals
for
use
by the
control section.
The
control
section continuously operates
the bipolar transistor
switch
and
varies the proportion
of
ON
time
to
OFF
time
in
response
- 155 -