| 摘要 |
<p>PURPOSE:To make it possible to obtain a good characteristic by preventing the saturation of an operational amplifier even at the time of overload, by directly converting an AC current to an AC voltage signal at the time of normal load but converting the current to the voltage signal by a resistor at the time of overload to perform amplification. CONSTITUTION:Because a load change-over switch sf has been set to an ON- state at the time of normal load, the AC current ie' outputted from the secondary side of a current transformer 1 is sent to an operational amplifier 11 through a resistor R12 to be converted to an AC voltage signal ie which is, in turn, sent out as a DC voltage signal (v) through a rectifier circuit 3 and a smoothing circuit 4. When the level of the DC voltage signal (v) reaches the level of a set signal vt at the time of overload, the load change-over signal K outputted from an operational amplifier 13 comes down to a low level to bring the load change-over switch sf to an OFF-state. Therefore, an AC current (i') is converted to an AC voltage signal ie<-> by a resistor R10 to be sent to the operational amplifier 11, where said AC voltage signal ie<-> undergoes voltage amplification to be inputted to the rectifier circuit 3.</p> |
