Patent attributes
A ventilating system that can make an air flow rate variable includes a DC motor that drives blades and a control circuit that controls the DC motor. The control circuit includes a first current detecting unit that detects a current flowing in the DC motor, a rotating speed detecting unit that detects a rotating speed of the DC motor, and a control unit that controls the DC motor based on a rotating speed detected by the rotating speed detecting unit and a current detected by the first current detecting unit. The current detecting unit includes a plurality of low-resistance resistors, detects a motor current by using divided voltages of the low-resistance resistors, and calculates a ventilation air flow rate based on the rotating speed detected by the rotating speed detecting unit and the current detected by the first current detecting unit.
