per step are As a digital-to-analog converter produces unwanted ohmic heatin the controller， pulse-width modulation is used instead to regulate the mean Simpler models switch voltage only for doing a step， thus needing an extra currentlimiter: for every step， they switch a single cable to the Bipolar controllerscan switch between supply voltage， ground， and Unipolar controllerscan only connect or disconnect a cable， because the voltage is already hard Unipolar controllers need center-tapped It is possible to drive unipolar stepper motors with bipolar The idea isto connect the output pins of the driver to 4 The transistor must begrounded at the emitter and the driver pin must be connected to the Collectoris connected to the coil wire of the Stepper motors are rated by the torque they Synchronous electric motorsusing soft magnetic materials (having a core) have the ability to provide positionholding torque (called detent torque， and sometimes included in the speci_cations)while not driven To achieve full rated torque， the coils in a stepper motormust reach their full rated current during each The voltage rating (if there isone) is almost The motors also su_er from EMF， which means that oncethe coil is turned o_ it starts to generate current because the motor is still There needs to be an explicit way to handle this extra current in a circuit otherwiseit can cause damage and a_ect performance of the 2 ApplicationsComputer-controlled stepper motors are one of the most versatile forms of positioningsystems， particularly when digitally controlled as part of a servo Steppermotors are used in oppy disk drives， atbed scanners， printers， plotters and manymore Note that hard drives no longer use stepper motors to position theread/write heads， instead utilising a voice coil and servo feedback for head Stepper motors can also be used for positioning of valve pilot stages， for uidcontrol
