Section III. DETAILED THEORY OF OPERATION

TM 32-5811-018-14&P

monitored by an external oscilloscope or voltmeter. Front-panel

indicators are used to monitor the status of the power supply

over-temperature sensors. The power supply external sense inputs are

provided by the power supply test set to compensate for test cable

loss.

The main power inputs are protected by ac and dc circuit breakers

mounted on the power supply test set front panel. Relays are

included to protect the power supplies from overheating by

interrupting dc power if ac (blower) power is absent. The ac and dc

power input lines are routed through EMI filters to eliminate

high-frequency line noise.

Eleven interface cables, including the power input cables, are

provided with the power supply test set. Instructions for operating

the test set are included in Chapter 6.

Section III.

DETAILED THEORY OF OPERATION

General.

5-4.

This section provides detailed circuit theory for the power

supplies. Since the three power supplies use sealed converter and

overvoltage Protector modules, the theory of operation in this

section is limited to a description of the main chassis of the power

supply units (see figures FO-1, FO-2, and FO-3) .

DC-DC Converter Power Modules.

5-5.

The dc-dc converter power modules for each power supply are

designated PS1 thru PS4. 28 V dc is applied in parallel to all of

the converter modules. Regulated dc outputs from the converter

modules are routed to the various system units via appropriate

interface connectors. Remote-sense dc returns are obtained from the

system units via interface connectors. Remote sensing permits a

converter module to regulate to the actual voltage at the load

because of the negligible voltage drop across the remote-sense return

line. For those modules not using the remote-sense feature (see

table l-l), the remote-sense input is jumpered to the dc output at

the converter module terminals.

5-6.

Overvoltage Protectors.

Overvoltage protectors U1 thru U4 are connected across the outputs

of the converter modules. For those converter modules providing both

positive and negative voltage outputs, the overvoltage protectors are

connected between positive and negative outputs. If an output

voltage or pair of voltages should exceed the limit set for the

corresponding overvoltage protector, crowbar action will cause the

protector to trip and present a low impedance that reduces the output

voltage to less than 1 V within 15 µs. When the cause of overvoltage

is removed, normal operation can be restored by momentarily deenergiz-

ing the power supply.

5-2