| 摘要 |
PURPOSE:To realize a current amplifying circuit which executes current amplification and, on the other hand, can reduce an input voltage on the opposite ends of a lead switch to be low, in a detecting circuit of the number of revolutions. CONSTITUTION:Between an input part of a lead switch 2 and an output part of a semiconductor device Tr1 for amplification in an input stage, a unidirectional semiconductor element D1 is provided, with a polarity directed from the input part toward the output part. The semiconductor device Tr1 for amplification is made to be ON when the lead switch 2 is OFF, and thereby a voltage impressed on the opposite ends of the lead switch 2 is reduced to be a forward drop voltage of the unidirectional semiconductor element D1. |
