Abstract: A trigger switch and lock mechanism therefore to be mounted in the handle of a drill housing for activating a motor of a drill wherein the trigger switch includes a speed control circuit carried on a circuit board. A trigger is slidably disposed in mounting brackets affixed on the circuit board. A locking member is slidably connected in one of the mounting brackets and is shiftable into contact with the trigger so as to lock the trigger in depressed position so that once the switch has been activated it will be locked in the "on" position at the selected speed setting. A spring is connected to the locking member to release the locking member from engagement with the trigger upon subsequent trigger depression to place the switch in the "off" position.The locking member and trigger have correspondingly high friction contact surfaces.

Abstract: Circuitry for rapidly switching off the power to a universal motor upon sensing of overloading of the motor. Sudden motor overloading results in rapid speed reduction that is detected by measuring the voltage drop across the motor armature. The circuitry detects this drop and removes a gating signal to a triac switch in series with the motor to remove the power to the motor within one cycle of the applied AC.