High Voltage Power Supply

TM 11-6625-467-34

high-voltage rectifier circuit. The high-voltage rec-

sients generated by the inverter circuit from enter-

tifier circuit produces 500-volt and 250-volt outputs.

ing the regulated 27.5-volt power supply circuit.

A conventional bridge rectifier circuit, consisting of

The inverter circuit consists of transistors Q4 and

diodes A7CR1 through A7CR4, rectifies the ac out-

Q5, saturable core transformer T2, resistors R24

p u t of transformer T2. T h e voltage across the

through R27, and capacitors C11 and C12. The volt-

bridge is 500 volts dc. Capacitors C4 and C5, con-

age divider consisting of R25 and R27 develops bias

nected across the bridge output, filter the 500-volt

for transistor Q4. Resistors R24 and R26 likewise

output. The center tap of the 500-volt transformer

develop bias for transistor Q5.

winding connects to the junction of the two filter

b. When operating voltage is initially applied to

capacitors. Diodes A7CR1 and A7CR4 function as a

the circuit, both transistors try to conduct. Circuit

c o n v e n t i o n a l full wave rectifier and place +250

tolerances and minor differences in the conduction

volts dc on the positive side of C4 with respect to the

c h a r a c t e r i s t i c s of the two transistors cause one

negative side. Diodes A7CR2 and A7CR3 likewise

transistor to conduct more heavily than the other.

function as a negative full wave power supply and

Assuming that transistor Q4 conducts harder, cur-

place a negative 250 volts dc on the negative end of

r e n t flows from ground through transistor Q4,

capacitor C5 with respect to the positive side. The

through winding 2-3 of transformer T2, and back to

net result is + 500 volts dc at the positive side of C5.

the +27.5 volt supply. This current flow induces a

The 5-ohm combination of resistors A7R16 and

voltage in winding 1-2 of transformer T2 that drives

A7R17 connects the negative side of capacitor C5 to

the base of transistor Q4 negative, and the collector

ground. The 5-ohm resistance develops a small dc

current increases. A voltage is also induced in wind-

voltage that is proportional to the circuit output

ing 4-5 of transformer T2 that drives the base of

current. Meter multiplier resistor A7R18 connects

transistor Q5 positive, and the collector current is

the dc voltage to the TEST METER through the

reduced. This action continues until the collector

current of transistor Q4 through winding 2-3 satu-

C I R C U I T SELECTOR switches. Resistors A7R5

and A7R6 are bleeder resistors connected across

rates the transformer core. When the core satu-

each leg of the power supply. The high-voltage

rates, the voltage induced in transformer winding

power supply operates anytime the 800-Hz inverter

1 - 2 drops to zero and the Q4 collector current

is energized; however, relay K1 prevents the high

decreases. As the Q4 collector current decreases,

voltage from appearing at RF CHASSIS connector

the magnetic field around transformer T2 collapses.

J2. Relay K1 energizes only when the three follow-

This action induces a voltage of the opposite polar-

ity in the transformer windings which results in a

i n g conditions exist: t h e POWER SELECTOR

positive voltage at the base of Q4 and a negative

switch is set to HIGH VOLTAGE, CIRCUIT SE-

voltage at the base of Q5; this condition causes tran-

LECTOR C is set to position 9 or 10, and an AN/

sistor Q4 to cut off and transistor Q6 to conduct

ARC-54 RF chassis is connected to J2. HIGH VOLT-

through winding 3-4 of transformer T2. The same

AGE ON indicator DS2 is connected in parallel with

action repeats as the Q5 collector current through

the coil of relay K2 and indicates that high voltage is

winding 3-4 saturates the core. Capacitors C11 and

present at J2.

C12 in the base circuits of transistors Q5 and Q4,

2-43. Power Supply Metering Circuit

respectively, couple the sharp leading and trailing

(fig. FO-2)

edges of the voltage waveforms on winding 1-2 and

3-4 to the bases of each transistor. The transistors

All power supply output voltages in the test set can

switch from conduction to nonconduction during the

be checked by the use of the test set TEST METER.

leading and trailing edges of the voltage wave. If the

P O W E R SELECTOR switch S1 connects meter

sharp rise and fall of these waveforms are pre-

multiplier resistors to the respective power sup-

served, the transistors switch more rapidly; there-

plies. The PRESS TO MONITOR VOLTAGE button

f o r e , less power is dissipated in the transistors

connects the selected meter multiplier resistor to

during the switching interval. The inverter output

the TEST METER. The TEST METER indicates 65

is a 54-volt, 800-Hz square wave that is symmetrical

percent if the power supply voltage is correct. The

with reference to ground. The output appears at the

TEST METER is protected against accidental over-

emitters of transistors Q4 and A5. Blower motor B1

load by two diodes, A15CR1 and A15CR2, in parallel

connects directly to the inverter output.

w i t h it. The forward conduction voltage of the

diodes is slightly higher than the full-scale voltage

2-42. High Voltage Power Supply

of the meter. When the full-scale voltage of the

(fig. FO-2)

meter is exceeded, the diodes shunt the excess cur-

The secondary winding on 800-Hz inverter trans-

rent around the meter. Each power supply metering

former T2 supplies approximately 500 volts ac to the

circuit is discussed in a through d below.

2-81