Fault protection circuit for an adjustable motorized hospital bed

Claim 1

A fault protection circuit for an adjustable motorized hospital bed wherein an AC power supply is coupled, via an isolation transformer, to a control system for the bed, comprising: a series circuit shunting the secondary winding of the isolation transformer and including, in the order named, a first diode, a first current limiting resistor, a pair of light emitting neon lamps, a second current limiting resistor, and a second diode poled oppositely to said first diode; a relay for controlling a pair of normally closed contacts in the circuit coupling the power supply to the primary winding of the isolation transformer; a photo-resistor optically coupled to both of said neon lamps and having a relatively high resistance when both of said neon lamps are off and a relatively low resistance when either one of said neon lamps is on; means for series-connecting said relay and said photo-resistor across the secondary winding; and means for grounding the junction of said neon lamps to the conductive frame of the hospital bed, said relay energizing and opening said normally closed contacts, thereby disconnecting the primary winding from the power supply, any time the failure oF a circuit component of the control system results in connecting either terminal of the secondary winding to the bed frame.