drill speed controller

C, 7 dril) speed controller This simple circuit is of interest because it enables drill speed to be controlled irrespective of the load on the drill. The design makes use of the fact that as the load increases the back EMF of the dril) falls and thus the current increases. It is clear, looking at the circuit diagram, that this circuit is not at all complicated, and the same is true of its operation. During the positive half-cycles of the mains C2 is charged up through R1 and Dl, until the voltage across this capacitor is equal to the "zener voltage" of the circuit at Ti. The circuit based on Ti is an adjustable zener in which the zener voltage is defined by the setting of Pl. In fact the voltage between collector and emitter is defined by 681 Rz Dz !AG the ratio between resistors R3 and R2 + Pl. The voltage drop across R3 is always equal to the base-emitter voltage of Ti (0.6 V) so it follows that the zener voltage is equal to P1 + R2+ R3 x 0.6 V. The motor is R3 not connected in ...