Stepper motor constant current drive circuit Theory
The principle of the constant current chopper is as shown in the figure below. When the rated current or the set drive current value is I0, the applied voltage is on the winding. If the set current value I0 is exceeded, the applied voltage V is turned off. The current is reduced. If the current value I0 is lower than the set current value, the applied voltage V is turned on, and the current is further increased to the set current value I0. Thus, I0 is a constant current. In the left figure, V and I represent 1 related voltage and current, and the 1 phase voltage is added to the t1 second time interval.
If the stepping motor rotates at a low speed, it does not need to be driven by a constant current chopper. When the current flowing through the motor coil exceeds the rated current, the motor will generate a high temperature rise and may burn out. In high-speed operation, if the time of the 1-phase winding voltage is less than t0 on the left, the power supply cannot guarantee the supply of the set current I0 value, and it becomes constant voltage drive. That is, in high-speed operation, there is a chopper that can become a constant current drive.
The reference voltage Vr corresponding to the set current I0 of the current measurement value is compared with the differential amplifier to a set current value and applied to the control terminal of the voltage chopper of the motor. Here, the constant current chopper circuit uses a constant voltage circuit. The comparison of the constant voltage and constant current pulse frequency-torque characteristic curves of the same stepping motor is shown in the figure below.
Both have the same torque when the same rated current is within about 10 pps, but the constant current chopper driver generates a large torque at low speed. Although the steady-state current values are the same, since the constant current chopper driver has a high current rise, its value is slightly higher than the average current value, and the above problems need to be noted in use.