Abstract: A dual AC input module providing AC line isolation of different phases without the use of relay control. Power supply load is supported through two AC line feeds, each feed being connected through a bridge rectifier to a common bulk DC power supply backplane. The parallel configuration of AC line feeds and bridge rectifiers eliminates the need for relay control logic to open relays and isolate a failed primary AC line feed prior to closing relays to connect a second AC feed to the power supply, as required with previous dual AC input module designs to isolate different line feeds of different phases.

Abstract: A switch mode power supply includes an AC to DC converter, a pulse width modulator for generating a series of pulses to control the switching of the DC across the primary winding of a transformer, and a start-up circuit connecting the AC to a power input of the pulse width modulator. A thermistor provides thermal protection for converter and start-up circuit components during abnormal operation, and a switch for disconnecting the start-up circuit and bypassing the thermistor after the power supply has been started improves power supply efficiency by eliminating power loss through the start-up circuit and thermistor.