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App note: Sensorless speed stabilizer for a DC motor

App note: Sensorless speed stabilizer for a DC motor

Precision Microdrives’ sensorless speed sense by exploiting speed dependent back EMF voltage. Link here

Motor speed is a parameter of a DC motor that is often measured and controlled, usually through additional sensors and with closed loop feedback. This method of speed control requires some form of speed sensor, normally mounted on the motor shaft. Some of our DC motors and gearmotors have rear shafts for just this purpose


Hall sensors and opto sensors are commonly used with digital controllers, whilst analogue circuits often use tacho-generators. With PWM control it is possible to achieve good accuracy, flexibility, and reduce power losses. However this comes at the cost of an additional component and potentially a mechanical design modification if you’re planning to use it in an existing product.

For brushed DC motors it’s possible to measure and control speed without any sensors on the motor, exploiting a basic characteristic – speed dependant back EMF voltage.