Motor drive device, electric blower, electric vacuum cleaner, and hand dryer

A motor drive device comprising:

• an inverter including a plurality of switching elements, the inverter converting a direct-current voltage output from a direct-current power supply into an alternating-current voltage by operation of the plurality of switching elements, and applying the alternating-current voltage to a motor;
• a control power supply outputting power having a voltage lower than the direct-current voltage, by using the direct-current voltage;
• a first signal generation unit driven by the power, the first signal generation unit generating drive signals driving the plurality of switching elements, and outputting the generated drive signals to the plurality of switching elements;
• and
• a power supply switch connected to the control power supply and the first signal generation unit,
• the power supply switch remains turned on so as to allow the control power supply to continue supplying the power through the power supply switch to the first signal generation unit to prevent a flow of regenerative current from the motor to the direct-current power supply when a rotation speed of the motor is higher than a threshold set to a rotation speed at which the direct-current voltage of the direct-current power supply is equal to an induced voltage of the motor, and
• the power supply switch is turned off so as to stop the supply of the power from the control power supply to the first signal generation unit when the rotation speed is lower than the threshold.