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Homebrew unipolar stepper driver with chopping current limiter.
This driver can deliver 24V/500mA per winding for a 2-phase unipolar stepper motor (so 1A total). It supports full-stepping mode with 3-wire control (one per phase + global enable).
Current limit can be adjusted through a potentiometer. It is done with a current sensing resistor whose voltage drop is compared with a reference voltage (set by the potentiometer) with some hysteresis. Current is controlled independently for each phase.
Switching is done at about 300-400kHz using power mosfets and a dedicated mosfet driver. Therefore, it produces no audible noise.
After a few minutes of continuous use (enable pin continuously on), current sensing resistors can get quite hot but they remain in their normal range (I used robust metal-oxyde 3W resistors). Mosfets remain quite cool.
Inputs: GND, +24V, +5V, phase A winding select, phase B winding select, enable.
Outputs: 6 wires for unipolar stepper