| 摘要 |
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. A timing-out circuit operates in conjunction with the sampling circuit to permit the sampling cycle to continue repetitively as long as an overcurrent condition is sensed. However, at the conclusion of a timing-out period which is a multiple of the sampling interval, if an overcurrent condition still exists, the timing-out circuit acts to reactivate the relay and cut off the delivery of current to the load and to hold the relay in its activated state.
|
