What is the difference between the unipolar and bipolar circuit?
Support » FAQ » Stepper motors
Unipolar controls are suitable for 5-wire, 6-wire and 8-wire motors and are used for simple and cost-effective applications. In the simplest case the positive supply voltage is applied to the middle tapping of the two phases and the respective winding halves are switched alternately to ground with only 4 switches or transistors (or also, for example, 4 outputs of the PLC) according to the wiring diagram. If stepper motors with relatively high winding resistance are used, the phase current is simply limited by the formula I = U/R or roughly by I = U/2 * π * f * L at high frequencies. Unipolar controls reach only about 70% torque compared to the bipolar control.
Bipolar controls are suitable for 4-wire, 6-wire and 8-wire motors and are used for high-performance and dynamic applications. The 2 phases are each connected to ground via two H bridges - 4 transistors are alternately diagonal according to the wiring diagram - from the positive supply voltage via the diagonal transistors (with constant current via a measuring resistor). The bipolar control has a torque that is approx. 30% higher (all of the copper is always used here) than the unipolar control. Highly integrated powerful constant current controlled microstep output stages such as the IMT 901, IMT 902 and SMC.. from Nanotec have been preferred for quite some time due to the high integration of the circuits and the higher torque.
