VOLTAGE SURGE PROTECTOR DIODE CR6:
Connected across transformer's power secondary winding.
Protects voltage regulator rectifier SCR1 (Q1) and bridge rectifier diodes CR1-CR4 from
transient voltage spikes.
V O L T A G E REGULATION CIRCUIT
Built into circuit card assembly PC101 (A1).
Controls firing time of silicon controlled rectifier SCR1 (Q1).
Keeps dc voltage at adjusted setting.
SCR1 (Q1) fires twice each cycle of ac input voltage. By controlling firing time, SCR1 (Q1)
can be varied from full on when fired at start of each half-cycle to full off when fired
at end of half-cycle.
Bridge rectifier's dc output voltage can thus be varied from maximum possible voltage to
Silicon controlled rectifier SCR2 (Q2).
Protects equipment being powered from overvoltages.
Activated when malfunction causes rise in output voltage.
C i r c u i t r y in PC101 (A1) senses trouble, fires SCR2 (Q2).
Firing applies short-circuit load to output terminals which reduces output voltage to very
Short-circuit load opens circuit breaker CB1, which turns power supply OFF.
This prevents possible damage to power supply and equipment being pawered.
VOLTAGE ADJUST CIRCUIT (DC OUTPUT)
Variable dc voltage adjust resistors R4, R8.
Do output voltage fed through resistors to PC101(A1).
Adjusts power supply's dc output voltage.
Activated when dc output voltage changes.