Power supply protective circuit

Claim 1

A protective system for a D-C power supply delivering current to an external load, the system distinguishing between a transitory overcurrent condition, in which case it functions to momentarily interrupt and then restore current flow, and a genuine overcurrent condition, in which case it functions to interrupt current flow and continuously maintain this interruption, said system comprising: A. a current-sensing resistor in series with said supply and said load, whereby the voltage drop developed across said resistor is proportional to the intensity of current drawn by the load; B. a voltage comparator responsive to said voltage drop to produce a low output signal when the drop reflects a current intensity below a predetermined threshold level and a high output signal when the drop reflects a current intensity at least equal to said level; C. a relay having normally closed contacts interposed between said resistor and said load, said contacts being opened when said relay is activated to interrupt current flow to the load, said relay being responsive to an activated by said high output signal; D. a sampling circuit rendered operative when said relay is activated and functioning after a brief sampling interval to de-activate the relay and thereby reconnect the supply to the load, at which point the comparator again determines whether the existing current drain is still excessive, in which event a high output signal is produced and the relay again activated to cut off the supply and to repeat the sampling cycle; and E. a timing-out circuit operating in conjunction with the sampling circuit and permitting sampling cycles to repeat as long as an overcurrent condition is sensed for a timing-out period which is a multiple of the sampling interval, the timing circuit at the conclusion of this period acting to reactivate the relay and cut off the delivery of current and to thereafter hold the relay in its activated state.