TM 5-6675-320-14
(b) Filtered dc is applied to the series switch pass transistor A9-Q1.
D r i v e c i r c u i t r y f o r t h i s t r a n s i s t o r a n d t h e c h o p p e r s t a g e t h a t f o l l o w s i t is
developed in PCA A10.
These drive pulse signals are present in the switching
section of the power supply assembly which is described next.
(2) Square - wave conversion circuit.
Converts the input dc to a square-wave
type of waveform.
(a) Applied dc is changed to a pulsed dc by pulsing the base of a
series switch pass transistor at a kHz rate.
A driving pulse train from PCA A10
(U3-6) turns on and off transistor A9-Q2.
While A9-Q2 is turned on, series switch
pass transistor A9-Q1 is reverse biased and, therefore, turned off. When A9-Q2 is
turned off, series switch pass transistor A9-Q1 is turned on and provides dc voltage
to energy storage inductor L2 which is connected to the chopper circuit.
PIN #4
PIN #5
PULSE WIDTH
MODULATOR INPUT
HIGH
LOW
PULSE WIDTH
MODULATOR OUTPUT
ON
AC POWER
SWITCH
OFF
EXPONENTIAL
TIMING SAWTOOTH
ON
SERIES PASS
TRANSISTOR A9-Q1
OFF
FILTER
CAPACITOR
A9-C24
TRANSISTOR
ON
A10Q2
OFF
TRANSISTOR
ON
A10Q1
OFF
TRANSISTORS ON
A10-Q3,
Q4 AND Q5
OFF
(b) A chopper circuit is used to convert the pulsed dc to a square-wave
type of waveform that is suitable as a transformer input to transformer T4. An 18
kHz chopper driving square-wave with a 50-percent duty cycle is supplied from PCA
A10-Q6 and A10-Q7, which alternately turns on either chopper transistors Q5 and Q4
or A6 and Q3.
The chopper driving square signal drives the primary windings of
transformer T3 whose secondary windings cause proper switching of the two pairs of
chopper transistors Q5 and Q4 or Q6 and Q3.
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