Despike Testing Circuit

TM 11-6625-467-34

+27.5 volt rectifier by POWER SELECTOR switch

the output of the bridge rectifier circuit and applies

it to the collector of transistors Q2 and Q3. Tran-

S1 when it is in the DESPIKE position. The addition

of the voltage boost circuit increases the dc input to

sistors Q,A6A1, A6A5 are cascaded voltage and cur-

rent amplifiers which sample the output voltage,

the regulator circuit approximately 15 volts-. The

POWER ENTRANCE switch also applies operating

amplify any change, and apply a control signal to the

voltage to the multivibrator circuit composed of

bases of series-regulator transistors Q2 and Q3.

a For the following discussion, assume the

transistors A6Q6 and A6Q7 and associated compo-

nents. The multivibrator oscillates at a frequency of

POWER SELECTOR switch S1 is in the - 27.5V

approximately 100 Hertz. The output of the multi vi-

position (as shown). Z e n e r diodes A6CR5 and

brator is nonsymmetrical; the negative portion is

A6CR6, in series with resistors A6R18 and A6R17,

approximately 10 milliseconds wide, and the posi-

form a voltage divider across the regulator output.

tive portion 90 milliseconds wide. Duty cycle control

The three Zener diodes have a constant 18.8-volt

A6R23 adjusts the output of the multivibrator for a

drop across them regardless of the regulator output

symmetry ratio of 9 to 1. Resistor A6R27 couples

voltage; therefore, any change in the regulator out-

the output of the multivibrator to transistor A6Q8.

put voltage appears entirely across resistors A6R17

Transistor A6Q8 is turned on for 90 milliseconds and

and A6R18. Resistor A6R18 is the regulator output

voltage control. Zener diode A6CR7 places a con-

off for 10 milliseconds.

b. During its conducting period, transistor A6Q8

stant 5.6-volt reference voltage on the emitter of

clamps the base of Q6Q1 (part of the +28-volt regu-

A6Q5.

b. To analyze the circuit operation, assume that

lator) at ground potential and thereby reduces the

power supply output to nearly zero. During the 10-

the regulated output voltage rises. A positive-going

millisecond period that A6Q8 is not conducting,

v o l t a g e appears at the movable arm of resistor

transistor A6A5 regains control of the base of A6Q1.

A6R18 and is direct coupled to the base of A6Q5.

During the 10-millisecond period, the +28-volt regu-

Transistor A6Q5 amplifies and inverts the positive-

lator operates normally as described in paragraph

going voltage and applies a negative-going voltage

2 - 3 9 ; except the DESPIKE AMPL control R5

to the base of A6Q1. Transistors A6Q1 and Q1 are

adjusts the power supply output amplitude rather

emitter followers that amplify the current output of

than A6R18. During the 90-millisecond period that

A6Q5 to a sufficient magnitude to drive series-regu-

the base of A6Q1 is clamped at ground, the output of

lator transistors Q2 and Q3. No phase inversion

the power supply is clamped at approximately 5

occurs in the emitter follower circuits; therefore,

emitter follower Q1 applies a negative going signal

volts dc. The resultant output of the +27.5-volt

power supply during the despike mode of operation

to the bases of series-regulator transistors Q2 and

is a positive 10-millisecond pulses with an amplitude

Q3. The negative-going signal at the base of Q2 and

of 22 to 50 volts peak as set by the DESPIKE AMPL

Q3 increases the internal resistance of the transis-

control. POWER SELECTOR switch A1A (section

tors and thereby decreases the output voltage back

Y) disconnects the blower circuit during despike

to the original value. Resistors R11 and R12 balance

operation. The +27.5 volt power supply filter, con-

the current flow through transistors Q2 and Q3 by

sisting of Cl, C8, C9, C10, and R22 and R23 is also

compensating for slight differences in conduction

disconnected and enables the power supply output

characteristics of the transistors.

to be pulsed.

2-40. Despike Testing Circuit

2-41. 800 Hz Inverter

(fig. FO-2)

The despike testing circuit consists of the +28-volt

a. The 800-Hz inverter is a saturable core,

regulator (para 2-39), a voltage boost rectifier cir-

square-wave oscillator that produces 54 volts ac to

c u i t , and a multivibrator. The purpose of the

operate the blower motor. A secondary winding on

despike testing circuit is to develop a pulse in the

the saturable core transformer furnishes 500 volts

output of the +27.5 volts dc power supply to test the

ac for the high voltage rectifier circuit. The +28-volt

despike circuit in the AN/ARC-54 power supply

dc regulator supplies operating power to the invert-

module.

er circuit. Section Y of switch S1A connects +27.5

a. The despike circuits are energized when the

volts dc to the center tap of transformer T2 through

POWER SELECTOR switch is set to the DESPIKE

a filter circuit consisting of capacitor Cl, C8, C9, and

position. The voltage boost circuit is composed of a

C10 and resistors R22 and R23. Capacitors Cl and

b r i d g e rectifier circuit (diodes A8CR5 through

C8 provide filtering for the +28-volt dc regulator.

A8CR8) and an inverted L-type filter (inductor L1

The combination of capacitors C9 and C10 and resis-

and capacitor C7). The output of the voltage boost

tors R22 and R23 is a spike filter that prevents tran-

circuit is connected in series with the output of the

2-80