Speed control circuit for AC series motor - provides compensation for electrical supply voltage variations by use of trigger diode and series thyristor

摘要

The speed control circuit enables the voltage drop across the motor to be measured by an RC circuit (D1, R1, R4, C1) and used to control a trigger diode (D) which in turn triggers a thyristor (T) in series with the motor. The circuit comprises a stabilising circuit of a variable resistor (R2), and two capacitors (C2, C3) whose common point is connected to the trigger diode (D). In addition a reference diode (D3) is connected across the trigger capacitor (C1). The voltage on the trigger device is thus stabilised, eliminating mains fluctuations and their effect on speed.