The OFS350 series of open-frame ministepping drives offer a 3.5A output with a resolution of 400-12,800 steps/rev, a step phase sequencer with MOSFET three-state switching amplifiers and opto-isolated circuits. The amplifier regulates motor current by chopping at a constant, inaudible frequency. Phase current is selected from 32 levels by a DIP switch, which also controls the microstepping resolution. The OFS350-DRI ministepper drive accepts industry standard step and direction command signals from an external control source.