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Functional Description / Operation of Modules (Draft) 
 

The Power Supply is described in this section.  The information provided is sufficient to give service personnel a 

functional understanding of the module, allowing maintenance and troubleshooting to the module level.  Refer to 
the service manual for Maintenance and Disassembly/Reassembly Procedures for detailed removal or installation 

procedures for all modules in the station. 

Over-current conditions on either the 28.6 VDC or 14.2 VDC outputs cause the total supply to shutdown and try to 

restart.  If the over-current continues to exist, the power supply will ‘hiccup’ until the overload condition is removed, 

and will not be damaged by the overload.  The 28.6 VDC output is protected by a primary current sense method 
such that its current limit point varies depending on the load on the other outputs at the time.  The trip point for the 

14.2 V and 5.1 V outputs is greater than 115% of the maximum current specified for the outputs.  The power 

supply recovers automatically after the removal of the overload condition. 

The 28.6 V and 14.2 V outputs are protected from continuous over-voltages by detection circuits that cause the 

supply to shutdown and then try to restart itself.  If the over-voltage condition continues to occur, the supply goes 
into a ‘hiccup’ mode of shutting down and trying to restart.  If the over-voltage condition is removed, the supply 

automatically recovers.  In addition, the 14.2 V and the 5 V outputs are protected by crowbar circuits. 

An AC Fail detect signal is provided to indicate (when used with battery backup option) that the power supply is 

operating from an external dc source rather than the ac mains.  This signal is a TTL compatible output capable of 

sinking 1 mA, and is routed to the Station Control Module.  The active-low state indicates ac operation.  For the 
nominal 120 VAC operation, the signal is active-high impedance (indicating an ac mains failure) when the ac 

voltage is less than 85 Vrms, but more than the minimum voltage that guarantees that all outputs will be in 

regulation at full load.  For the nominal 240 AC operation, the detect point is less than 170 Vrms but more than the 

minimum ac input voltage that guarantees that all outputs be in regulation at full load. 

The supply incorporates temperature sense/fan enable circuitry for controlling a 12VDC fan mounted on the 
surface of the heatsink assembly. The power supply circuitry senses the internal temperature of the power supply. 

When the internal temperature exceeds +60°C (± 5°C), +12 V is enabled at J1–1 to turn on the fan. The +12 V fan 

supply is derived from the +14.2 V output. Power to the fan is off when the temperature is below the set limit. The 

fan turns for approximately 5 seconds when power is first applied as a diagnostic indicator that the fan is 

functional. 

The power supply will turn off all outputs when an operational ambient temperature of +80°C (±2°C) has been 

reached with the supply operating at any input within its operating input voltage range (dc and ac). 

The following shows the electrical performance specifications for the power supply. 

 

Power Supply Module AC Performance Specifications: 

 

Input Voltage Range 

85 VAC to 264 VAC 

Operating Temperature 

–30° to +60° C (–22° to +140° F) 

Input Frequency Range 

47 to 63 Hz 

Steady State Output Voltage 

28.6 V @ 13 A, 

14.2 V @ 8 A,  

5.1 V @ 2 A 

Output Power (Rated) 

500 W 

Output Ripple: 

+28.6 VDC 

+14.2 VDC 

+5.1 VDC 

 

50 mV p-p, @ 25°C (77°F) 

50 mV p-p, @ 25°C (77°F) 

100 mV p-p, @ 25°C (77°F) 

Efficiency 

Greater than 75% (Full Load)