TM 5-6675-318-14
(b) Filtered dc is applied to the series switch pass transistor A9-Q1.
Drive circuitry for this transistor and the chopper stage that follows it 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.
C o n v e r t s the input dc to a square-wave
( 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 PCAA10
( U 3 - 6 ) t u r n s o n a n d o f f t r a n s i s t o r A 9 - Q 2 . W h i l e 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
EXPONENTIAL
TIMING SAWTOOTH
PIN #5
PULSE WIDTH
MODULATOR INPUT
HIGH
ON
SERIES PASS
TRANSISTOR A9-Q1
LOW
OFF
PULSE WIDTH
MODULATOR OUTPUT
ON
AC POWER
sWITCH
OFF
CHARGING
FILTER
CAPACITOR
A9-C24
ON
TRANSISTOR
A10-Q2
OFF
ON
TRANSISTOR
OFF
A10-Q1
TRANSISTORS ON
A10-Q3,
OFF
04 AND Q5
(b) A chopper circuit is used to convert the pulsed dc to a square-wave
kHz chopper driving square-wave with a 50-percent duty cycle is supplied from PCA
A 1 0 - Q 6 and A10-Q7, which alternately turns on either chopper transistors Q5 and Q4
or A6 and Q3. T h e c h o p p e r d r i v i n g s q u a r e s i g n a l d r i v e s t h e p r i m a r y w i n d i n g s o f
transformer T3 whose secondary windings cause proper switching of the two pairs of
c h o p p e r transistors Q5 and Q4 or Q6 and Q3.
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