The universal motor is a rotating electric machine similar to a DC motor but designed to operate either from direct current or single-phase alternating current. The universal motor can be controlled either as a phase-angle drive or as a chopper drive.
In the phase-angle application, the phase-angle control technique is used to adjust the voltage applied to the motor. A phase shift of the gate's pulses allows the effective voltage, seen by the motor, to be varied. The phase-angle drive requires just a triac.
In the chopper application, the Pulse Width Modulation (PWM) technique is used to adjust the voltage applied to the motor. Compared to a phase-angle drive, a chopper drive requires a more complicated power stage with an input rectifier, a power switch and a fast power diode. The advantage is higher efficiency, less acoustic noise and better EMC behavior.
