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Power Supplies
Standby Power Supply
Figure 29
The standby power supply provides the necessary DC voltage for the system
control Microprocessor, Reset circuit and the EEPROM. D421 rectifies the
incoming AC Voltage and applies it to the transformer T402 and the standby B+
control circuit IC400. The output pulses of IC400 are then applied to the primary
side of transformer T402. Diode D439 rectifies the AC output at pin 15 of the
secondary of T402 to create STB (Standby) voltage for the system control circuit.
The AC output at pin 14 of the secondary of T402 is rectified by diode D440 to
create the DC voltage for the power relays. Transistor Q418 creates the ground
path for power relay RL401. Transistor Q417 provides the ground path for the In
Rush Current relay RL400. The Opto-coupler D431 provides feedback to the
STB control circuit for voltage regulation.