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Figure 25. Voltage regulator module A16, schematic diagram.
tors Q1 and Q2 switch rapidly from
condition induces a voltage in the
cutoff to saturation, the current in
feedback winding of transformer
transformer T1 is essentially a
T1. The voltzage is applied to the
square wave.
bases of the transistors, causing
b. Inductor L1 and capacitors C1 and C2
Q1 to conduct even more, and driv-
form a pi-type filter circuit which pre-
ing Q2 further into cutoff. The flux
vents voltage peaks developed in module
in the core of transformer T1
Al from reaching the 12.5-volt supply. A
changes at a nearly constant rate
voltage divider, consisting of resistors
until the core is saturated. When
RI and R2, establishes the fixed base bias
saturation occurs, no voltage is de-
for transistors Q1 and Q2.
veloped in the feedback windings of
c. The rectifier circuit consits of two
transformer T1. The feedback volt-
full-wave rectifiers. The 125-volt output
age to transistor Q1 decreases
is rectified by diodes CR1 and CR4 and
rapidly and drives transistor Q1
filtered by capacitor C4. The -45-volt out-
into cutoff.
put is rectified by diodes CR2 and CR3,
(2) When transistor Q1 cuts off, the
and filtered by inductor L2 and capacitor
flux in the core of transformer T1
C3. Resistors R4 and R5 are isolating re-
decreases slightly to induce volt-
sistors which prevent circuit loading by
ages of opposite polarity across
test equipment probes placed at voltage
its windings. This reversal of po-
larity drives transistor Q1 further
test jacks J2 and J3. Resistor R3 is a
bleeder for the +125-volt output.
into cutoff and causes transistor
Q2 to conduct. The current through
Q2 increases until the transformer
32. Test Points
core saturates, and the cycle then
The RT-505/PRC-25 has 28 test points
repeats. During each half cycle,
located on 21 modules which enable a main-
the transformer flux changes from
tenance man to locate a faulty module
saturation in one direction to sat-
rapidly. These test points are normally
uration in the other. Since transis-

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