DC Motor Drives

DC motor drives act as an interface between a controller and the motor. The drive must match the control signals (voltage and power levels) and signal type (analog or digital). The drive produces power conversion, amplification, and sequencing of waveform signals.  Types of DC motor drives include adjustable or variable speed control, servo control, and integral motion control.  Some drives are capable of delivering adjustable or variable speed control.  Servomotors are generally small, powerful for their size, and easy to control.  Integral motion control includes feedback and a controller.  Important specifications to consider when searching for DC motor drives include considering whether or not a brushless DC motor drive or amplifier is needed.  Some DC motor drives operate in conjunction with a brushless DC motor.  Types of DC brushless motor drives include sine wave, trapezoidal, hall sensor commutation, and no sensor.  

Important operating specifications to consider when searching for DC motor drives include open loop control, positive feedback, tach or velocity module, BEMF or voltage control, torque or current control mode, switching frequency, bandwidth, maximum speed, continuous power, continuous output voltage, maximum continuous output current, and peak output current.  Open loop control uses a tachometer or other device to monitor motor speed, rather than using position feedback to control motor.  Position feedback uses position, force, or other feedback to control motor, in addition to speed sensors.  Use of feedback is referred to as "closed-loop control."  A tach or velocity mode gives direct feedback of motor speed.  A drive with BEMF or voltage control can run without a tach using the motor's Back EMF voltage.  A torque or current control module has constant current control, uses current feedback.  Switching frequency is specified for drives with digital output waves, i.e., PWM.  The bandwidth is the frequency range over which the device meets its accuracy specifications. Accuracy is degraded at lower and lower frequencies unless the device is capable of dc response, and at higher frequencies near resonance and beyond, where its output response rolls off. Frequencies in the database are usually the 3dB rolloff frequencies.  The maximum device speed is the speed when the drive is burdened with no external forces, such as weight.  The continuous power is the maximum amount of power the device can output continuously.   The continuous output voltage is the maximum voltage the device can output continuously.  The maximum continuous output current is the maximum current the device can output continuously.  Maximum current value may require additional cooling.  The peak output current is the peak current the device can output.

Interface options to consider when searching for DC motor drives include analog or digital drives.  Manual adjustments are available for some drives.  These include potentiometers, dip switches etc. for adjustment/set-up, not for daily use.  An interchangeable module or EPROM is a 'module' that holds motor parameters to match a drive to a motor. Interchangeable modules allow the device to drive different motors.  Computer interfaces and self-test diagnostics are also common features.  Other important features to consider when specifying DC motor drives include PWM switching, dynamic braking, and regenerative braking.  PWM or switching drives have an output that is pulse width modulated or switching.  Dynamic braking uses a shunt resistor or direct short across the armature to reduce mechanical energy.  Energy is dissipated to the environment as heat.  Regenerative braking converts mechanical energy back to electrical energy and transfers it back to the energy source.  In this form of braking, mechanical energy is fed back through the power transmission system and the motor acts as a generator to convert mechanical energy into electrical energy.  Newly converted energy is stored in a battery.  Regenerative braking is often used in conjunction with dynamic and other braking methods.  An important environmental parameter to consider for DC motor drives is the operating temperature.

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Part Numbers for DC Motor Drives