Motor Drives

Find the right TI devices, software and support to precisely control motor position, velocity and torque. Browse by industrial applications including Robotics, AC Inverters, Servos, Hoists, Power Tools, CNC and Textile Machines or by motor types: DC or brushless DC, steppers, PMSM and AC Induction Motors.


Brushed DC Motors - Overview

Motor Control - Brushed DC Motors Overview

Brushed DC motors are one of the oldest motor topologies in existence today. They use stationary brushes mounted to the stator frame which rub against commutator segments on the rotor, which in turn are connected to the rotating coil segments. As the rotor spins, different rotor coils are connected and disconnected in such a way that the net magnetic field produced by the rotor is stationary with respect to the stator frame, and properly oriented with the stator magnetic field so as to produce torque. As the commutator segments rotate past the brushes, the electrical contacts to those particular rotor coil segments will be broken. Since the rotor coils are inductive, and inductors oppose changes in their current by generating a high flyback voltage, sparks are produced between the brushes and the disconnected commutator segments. These sparks result in many negative consequences, such as electrical noise, reduced efficiency, and in some cases, hazardous operation. Furthermore, the brushes must be spring loaded against the commutator segments in order to insure good electrical contact. This further reduces efficiency, and requires periodic maintenance to replace the brushes.

Despite these disadvantages, the brushed DC motor has one significant advantage…cost. Since controlling a brushed DC motor is relatively simple, they are still used extensively in applications where system cost is the primary driving factor. In topologies which use permanent magnets to generate the stator flux, the resulting speed/torque curve is extremely linear. For this reason, brush DC motors have historically been popular in industrial servo applications, since speed and torque are directly proportional to the applied voltage and current respectively. However, the falling cost of semiconductor devices has resulted in lower costs for power conversion and control. Because of this, many DC motors are being replaced with AC motors, which offer many advantages such as increased efficiency and reliability.

There are several variations on the brush DC motor theme, such as the DC shunt motor, and the universal motor, which both utilize a coil in the stator instead of permanent magnets. In a DC shunt motor, the stator coil is connected in parallel with the rotor circuit, and the universal motor has its stator coil connected in series with the rotor. The universal motor in particular is popular in household appliance applications because of its high starting torque and high speed operation. Speed control of universal motors is easily accomplished by simply adding a series thyristor and performing AC phase control. However, the brush/commutator structure is common to all of these motor types, and as a result, they share the same disadvantages as the standard PM brush DC motor.