f)
During
Q1
is
ON, input vonage Yin
is
added on the primary
winding P But,
it
is
added on
Q1
C-E
suddenly.
g) At same time, inverted voltage appears at
"B"
which will bias
Q1
B·E reversely and
Q1
is OFF.
h) The energy charged in
P
is
discharged
by
the secondary
winding S thru D909.
i)
Q1
B-E
biased reversely.
j)
The energy
is
discharged thru D909 and when
Id
is
zero,
starting current
by
R902 makes
Q1
on again.
Repeating from
(a).
2. Operation circuit
(1) The operation Circuit has function for voltage regulation
in addition to the basic
cirCUIt.
When the output voltage
is
going to increase. base drive cur·
+
Yin
here:
(In the actual case, restart
is
made by leakage inductance of
the transformer and after starting by R902, switching of
Q1
is
kept continuously without R902.)
* Energy charged
in
P
is
1/2
X
Ll2
* The curves of collector current
at
Increasing
is
soft
if
induc·
tance
is
large. The larger, the softer.
Natural fold back characteristics
is
given to
this
circuit against
over load and output short, so, addibonal protection circuit
is
not needed.
rent
is
going
to
decrease,
so
that
Ql
IS
switched off during
small collector current and the output voltage
is
regulated.
.---Dl-
__
~
+
0909
S C920
Vout
•
________________________
J
If
the output voltage
is
going to exceed rated voltage. Q3
IS
switched on and Q2
is
switched on and base current for
Ql
IS
proportionately decreased Voltage regulation
IS
done like
this.
Yin
Switching frequency F
IS
X k
lout x L
proportionate to input voltage and reversely
proportionate to output current and inductance.
+
3
fo.-.
__
--.
(2)
If
the output voltage
is
directly detected. the regulation ac·
curacy
is
Improved. But the secondary will not be insulated
from primary. (Hot chassis)
In
order to make cold chassis.
voltage detecting winding
is
to be added. The output voltage
IS
regulated indirectly and secondary
w,1I
be insulated from
primary.
When this detecting winding
is
added. the Winding construc·
tlon
is
to be conSidered
to
get coupling characteristics. Split
each winding Into two and construct sandwich windings to im·
prove load regulation.
0909
.--1::.1--_---0
+
C920 Vout
s
•
I
~---~T-----------~2:
L
___________
- -
--
- - - - -
-_
...
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