Abstract: A protective system interposed between a d-c power supply and an external load to isolate the supply from the load should the current drawn therefrom exceed a predetermined threshold value, the system distinguishing between a transitory overload and a continuous overload condition. The system includes a current-sensing resistor connected in series with the supply and the load and a comparator responsive to the voltage drop developed across the resistor to produce an output signal which activates a relay to cut off the delivery of current to the load only when the current exceeds the threshold value. Also included is a sampling circuit which upon activation of the relay functions after a brief sampling interval to automatically de-activate the relay and thereby reconnect the supply to the load, causing the comparator to again determine whether the existing current drain is still excessive, in which event the relay is again activated and the sampling cycle repeated.

Abstract: A rapid-response overload protector interposed between a voltage source and a load powered thereby, the protector effectively decoupling the load from the source when the current drawn thereby exceeds a predetermined limit indicative of an overload condition. The protector includes an automatic resetting stage that periodically samples the state of the load and acts to restore the normal supply of current thereto when the current drawn by the load during the sampling interval falls below the limit.

Abstract: A protective relay circuit operating in conjunction with a regulated direct-current power supply in which a rectified A-C voltage having a ripple component is fed to an output terminal coupled to a load through the choke of a filter network. The excitation coil of a relay is connected between the input of the choke and the output terminal whereas the normally-closed relay switching contacts are interposed between the output of the choke and the output terminal. The relay coil has a high impedance relative to that of the chokes so that in normal operation, the coil has virtually no influence on the filter and does not pass the ripple component to the output terminal. In the event of a short effectively grounding the output terminal, the unfiltered rectified voltage is then imposed across the excitation coil to activate the relay and open the switching contacts, thereby disconnecting the supply from the shorting load.