| 摘要 |
PROBLEM TO BE SOLVED: To provide a rotational speed detection device capable of detecting the rotational speed of an electric motor using a low voltage.SOLUTION: A control voltage detector unit 321 detects a control voltage Vsu1 applied to one of control electrodes of a pair of switching elements 1xp, 1xn. A pulse/sine wave converter unit 322 averages the control voltage and converts the control voltage into a sinusoidal voltage WV1 in a substantially sinusoidal shape. According to a comparison result of the sinusoidal voltage WV1 with a predetermined value, a comparison unit 323 outputs a signal PS1 for activation/deactivation. A rotational speed calculator unit 324 detects the frequency of the signal PS1, to calculate the rotational speed of the electric motor on the basis of the frequency. |
