| 摘要 |
PURPOSE:To obtain a driving device for an AC motor of low cost and high reliability by detecting a voltage phase and by converting from the voltage phase to the current phase in the volume proportional to the power factor obtained through at least one transformer. CONSTITUTION:With a transformer 41 the voltage phase is detected, with the output signal of which the volume proportional to the power factor is detected by the power factor detection circuit 43 inputting the current detection signal from a transformer 42. Besides this, the output signal of the power factor detection circuit 43 is held in volume by a holding circuit 44. In a current phase arithmetic circuit 45 the current phase is operated from the volume held in proportion to the voltage phase and the power factor, so that a signal is outputted to a phase comparator 35. A running signal RUN is also inputted to the holding circuit 44. As long as the running signal RUN is not inputted, the output signal of the holding circuit 44 is outputted in the same volume as that of the input signal. When the running signal RUN is inputted, the outputted signal then is kept holding as it is. |
