Constant Current and Constant Voltage Driver

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Constant Current and Constant Voltage Driver

Postby om_tech_support_JT » Tue Jun 05, 2012 4:41 pm

Q: I am trying to select a stepper motor/driver package for my application. After research, I learned that there are two types of drivers: constant current drive and constant voltage drive. How are they different and what type of driver does Oriental Motor provide?

A: Constant voltage drive is also referred as L/R drive circuits. This type of driver will supply a constant voltage to each stator winding. Since it is the current that goes into the winding and produces torque in a stepper motor, the current I is related to the voltage V, inductance L, and winding resistance R. R will determine the maximum current in the winding and L will determine the rate of change of current in the winding. The maximum speed of the stepping motor is limited by L/R constant, which represents the rate of change of the current. At higher speed, current change can not keep up with the pulse frequency, thus the torque will be reduced at high speed. In order to increase the torque, we can reduce the L/R constant by adding another resistor in series with the coil to increase the resistance R value. However, voltage also needs to be adjusted to compensate for the power loss on the external resistor. This method will result more energy loss since the external resistor will also draw electrical power according to the formula P=I^2 R.

Constant current drive is also referred as chopper drive circuits. On each step, normally a voltage higher than the rated voltage of the motor is applied to the winding. This will cause the current in the winding to rise quickly since the rate of change of the current is determined by the inductor formula dl/dt = V/L. With a large voltage L, the current in the winding rises quickly. This current is monitored by the driver circuit so that it will turn the high voltage on and off to maintain a relative stable current in the windings. Current is measured based on a voltage over a current detection resistor and this current will be compared with a reference voltage. Depending on the comparison, a transistor will turn on and off at an appropriate pulse width to keep the current constant. This method will require additional electronics to monitor the current in windings. And the benefit is that the characteristics in high speed region are significantly better than that of constant-voltage drive.

Oriental Motor driver products are of constant current drive type. Also most of the drivers except the UMK series feature microstepping functions to reduce the vibration and provide a smoother motion. Oriental Motor offers a variety of stepping motor/driver packages including the AC input RK and UMK series; DC input CRK, CMK and RBK series, and proprietary alpha step closed loop AR and AS series available in either AC or DC input. Please follow the link below to browse our stepping motor products:

Please feel free to contact our technical support group if you have any questions.

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