Patent ID: 8093847

Claim:
A motor driving circuit which drives a multi-phase motor having coils by supplying a driving current to the multi-phase motor, comprising: a plurality of switching circuits each of which is provided for a corresponding coil of the multi-phase motor, and each of which applies a high-level voltage or a low-level voltage to one terminal of the coil connected to the switching circuit; a back electromotive force detection circuit which detects a zero-crossing point by making a comparison between a back electromotive force which occurs in at least one coil of the multi-phase motor and a center tap voltage at a common node of the coils, and outputs a back electromotive force detection signal; a switching control circuit which controls the switching state of each of the plurality of switching circuits based upon the back electromotive force detection signal output from the back electromotive force detection circuit so as to adjust the current that flows through the coils of the multi-phase motor; and a window generating circuit which outputs a window signal which is maintained at a predetermined level during a period of time obtained by multiplying the cycle of the back electromotive force detection signal output from the back electromotive force detection circuit by a predetermined coefficient before the detection of the zero-crossing point by means of the back electromotive force detection circuit, wherein, during a period of time in which the window signal output from the window generating circuit is maintained at the predetermined level, the switching control circuit stops the switching operation of the switching circuit, thereby setting the switching circuit to a high-impedance state.