Circuit Analysis

TM 11-5895-932-14&P

When the power supply is overloaded in excess of

As the core approaches saturation, it cannot carry

its rated load, a point is reached where the output

much additional magnetic flux, and the increase in

voltage drops to approximately zero. Due to the

secondary voltage is less than any proportional

magnetic shunt in the transformer, its output

increase in primary voltage. Thus, a condition of

current is limited. With excessive load current, the

relative stability of secondary voltage is reached.

effect of the ac capacitor is lost: secondary flux

Over the range of specified primary voltage, the

opposes primary flux to demagnetize the secondary

core under the secondary winding is magnetically

core leg and the output voltage collapses, limiting

saturated, and the voltage of the secondary changes

current to approximately 150 percent

short-circuit

very little for this range of primary voltage. Due to

of full load.

the magnetic shunt between the primary and

secondary windings, that part of the core under the

F-3. Maintenance

primary is not saturated

This regulated power supply is designed for

To equalize the small effect of increasing primary

continuous, unattended operation. Little or no

voltage on the secondary, a compensating coil is

maintenance is required. If due to a component

wound over the primary coil and is connected in

failure maintenance is required, be sure to shut off

series with the secondary load circuit, but out of

line voltage prior to performing any repair

phase with the secondary. Thus, when the primary

operations. Discharge any residual charge on the

voltage increases beyond the design voltage, the

dc filter capacitors by connecting a jumper across

voltage in the compensating coil also increases, but

the output terminals or across the dc capacitor

since it is out of phase with the secondary voltage,

terminals, or allow at least one minute to elapse

it subtracts from the secondary voltage an amount

after shutting off line voltage to permit the

equal to the slight increase induced in the

capacitors to discharge. The energy stored in these

secondary winding by the increase of primary

capacitors could be harmful or fatal to personnel.

voltage. Likewise, when the primary voltage

F-4. Circuit Analysis

decreases, the compensating coil voltage decreases

The chart below lists some possible malfunctions

in proportion to the primary voltage, and subtracts

which may be encountered in the use of the supply

from the secondary voltage. The design is such

and their corresponding cause and remedy.

that the vector sum of the compensating coil

voltage and the secondary voltage is practically

constant throughout the design range of input

voltage.

Corrective action

Probable trouble

Symptom

a Correct load current

a Load current less than minumum rated

Output voltage too high

load

b Correct primary power frequency

b Line frequency too high

a Reduce load current

Output voltage too low

a Load current greater than maximum

rated load

b Line voltage too low

increase primary voltage

Correct primary power frequency

c Line frequency too low

d Defective dc filter capacitor

Replace

e Defective ac capacitor

Replace

f Defective rectifier

a Check all connections and repair bad

No output voltage

a Open connection

connections

b Replace transformer

b Open transformer winding

F-3