Methods for Eliminating Noise of Brushed DC Motors

The DC brushed motor generates a lot of noise when working, which often causes the microcomputer to work abnormally.

The above figure shows the internal structure of a brushed DC motor. The commutator on the rotor rotates with the rotor and keeps in contact with the two brushes in turn. When the motor rotates, sparks are generated between the commutator and the brushes, thus generating noise with a wide frequency range.

If you place an AM radio near a rotating brushed DC motor, you will hear the noise produced by the motor in the radio.

In order to eliminate the noise generated when the motor rotates, a capacitor is often connected at both ends of the motor. The capacitor is used to absorb the noise. The capacitor must be as close to the noise source as possible and should be installed directly on the motor terminal. The motor with metal brushes generates more noise. For this type of motor, the capacitor is not ideal in suppressing noise. Increasing the capacity of the capacitor can change the effect of absorbing noise. But it often brings new problems, that is, the leading and trailing edges of the waveform of the drive signal will become blunt during PWM control.

In this case, we must think of ways to route the power supply line and ground line. As shown in the figure below, in addition to adding a filter to the power line of the microcomputer circuit board, the power line of the microcomputer and the power line of the motor should be separated, and the ground line should also be routed separately. If the problem still cannot be solved, use two independent power supplies to power the microcomputer and the motor respectively.