Stepless speed regulation circuit using auxiliary power supply

 The circuit is shown in Figure 3-171. In the figure, the auxiliary power supply is a single-phase AC power supply , and the output current is supplied to the balancing resistor R through the single-phase half-wave control bridge (
composed of diodes VD7, VD8 and thyristors vl, V2). , the trigger circuit of the thyristor is a full-
wave resistor-capacitor phase-shift bridge.
    By adjusting the potentiometer RP, the trigger conduction angle of the thyristor can be changed, so that the motor can
be continuously adjusted within the range of 300 to 900r/min.