Patent ID: 7960929

Claim:
A motor driving device, which drives a motor, comprising: an output circuit that is driven by a first power supply voltage, includes a switching element of which turning-on/off is switched according to a switching control signal, and outputs current corresponding to the pulse width of the voltage to motor coils when receiving a pulse-width-modulated first power supply voltage; a start logic circuit that controls a rotational speed of a rotor of the motor below a threshold; a control circuit that is driven by a second power supply voltage and that includes a position detecting circuit and a switching circuit, the position detecting circuit detecting the position of the rotor by detecting counter electromotive forces that are generated in the motor coils during the rotation of the rotor to control the rotational speed at and above the threshold, the switching circuit generating a switching control signal on the basis of the detection result of the position detecting circuit in order to switch the turning-on/off of the switching element; a backflow preventing diode; and a capacitor that performs a charging operation by a voltage that is applied from an input terminal of the first power supply voltage through the diode, the capacitor applying a charging voltage of a node between the diode and the capacitor to the control circuit as the second power supply voltage during a period when the first power supply voltage is not applied, the backflow preventing diodes prevents backflow of charge accumulated in the capacitor.