Self-protective fuel pump driver circuit

Abstract

A self-protective driver circuit with automatic reset features is provided for a marine electric fuel pump (2, 102) energized by the boat battery (4, 104) as controlled by a series connected semiconductor switch (6, 106). A first stage protective subcircuit (28, 128) senses surge current through the semiconductor switch at initial turn on with the fuel pump at rest and causes the semiconductor switch to depart from saturated conduction and thus limit the current until the pump starts running and the current decreases to a safer level, to protect the semiconductor switch from excessive current. A second stage protective subcircuit (36, 136) senses a given minimum current flow through the semiconductor switch in combination with abnormally high conduction voltage across the semiconductor switch, indicating a stalled or electrically shorted fuel pump, and in conjunction with a timer (58, 164) quickly turns OFF the semiconductor switch for a given time interval for cooling-off purposes, after which the semiconductor switch is automatically turned back ON, with the cycle repeating as necessary. A third stage protective subcircuit (82, 184) senses long term increased current flow through the semiconductor switch indicating a deteriorating condition in the fuel pump, and in conjunction with the timer turns OFF the semiconductor switch for the given time interval after which the semiconductor switch is automatically turned back ON to re-energize the fuel pump, the cycle repeating as necessary.