A drive control signal is effectively obtained. An offset control circuit ( 32 ) adds an offset to a rotational state signal. An added signal is obtained by adding an offset to the rotational state signal by repeating a process in which, when it is detected that an added signal in which a predetermined offset amount is added to the rotational state signal on a side approaching a reference value becomes the reference value from one direction at a first time, the offset amount is added to the rotational state signal in a direction returning from the reference value, when it is detected that the obtained added signal becomes the reference value from the one direction at a second time, no value is added to the signal, and, when it is detected that the added signal becomes the reference value at a first time from another direction which is a direction opposite to the one direction and which reaches the reference value, the offset amount is added to the rotational state signal on a side approaching the reference value. A drive control signal is generated in which the level is reduced compared to the sine wave shape signal for a predetermined period of the obtained added signal between the reference value at the second time and a reference value at a next time.
1. A driver circuit which generates a drive control signal based on a rotational state signal of a sine wave shape which indicates a rotational state of a motor, comprising:
an added signal generating circuit which obtains a first added signal or a second added signal in which an offset amount is added to the rotational state signal by repeating a process in which, when it is detected that the first added signal in which a predetermined offset amount is added to the rotational state signal on a side approaching a reference value becomes the reference value from one direction at a first time, the offset amount is added to the rotational state signal in a direction returning from the reference value to obtain the second added signal, when it is detected that the obtained second added signal becomes the reference value from the one direction at a second time, no value is added to the signal, and, when it is detected that the second added signal becomes the reference value at a first time from another direction which is a direction opposite from the one direction and which reaches the reference value, the offset amount is added to the rotational state signal on the side approaching the reference value, to obtain the first added signal, and
a drive signal generating circuit which generates a drive control signal having an electricity application period from a time when the obtained added signal becomes the reference value at the second time until a time when the obtained added signal becomes the reference value at a next time.
2. The driver circuit according to claim 1 , wherein
the drive control signal generating circuit generates a different drive control signal between a time when the added signal is at a positive side and a time when the added signal is at a negative side.