Speed control circuit for D.C. motor - includes transistor forming comparator with reference resistance and thermistor across motor supply

摘要

The speed control circuit for a d.c. motor, uses a temp. responsive element (42) such as a thermistor, in parallel with a reference resistance (26) to compensate for changes in temp. These are connected in series with a f.e.t. (28) and resistor (8) forming a path across the motor (M) and its d.c. supply (18). In series with the motor and supply is a control transistor (16). The base connection of an equalising transistor (22) forming a comparator, is connected to the junction between the reference resistance and the thermistor. The collector of the equalising transistor is connected to the base of the control transistor.