A Brushless DC Motor Controlled by a Microprocessor with Examples for a Three-Phase Motor

The principle and the characteristics of a brushless dc motor and a driver circuit using bipolar transistors are described briefly. Motor control by microprocessor, including hardware and software commutation, speed measurement, and control via software algorithms, is described in more detail. Different current choppers were investigated: the hysteresis current chopper, the fixed-frequency current chopper, and the software current chopper (Patent EP 0 093 182 A1, US 4 514 667). Application examples and implementation details for the print-band drive of an impact printer are discussed. Finally, microprocessors are ideal devices to detect, to isolate, and to pass on errors for display.