| 摘要 |
PURPOSE:To reduce both a leakage current and residual voltage by flowing only the current that a sensor circuit requires at any time, by using a constant current circuit which performs constant-current operation even at a low voltage by using FET. CONSTITUTION:When the output of sensor part 51 is at H, transistor Tr3 is turned off, and Trs 2 and 1 are therefore both turned off to supply sensor part 51 with a current passed through constant current circuit 6, so that its voltage is stabilized by Zener diode ZD2. When the output of sensor part 51 is at L, Tr1-3 turns on. At this time, if the residual collector-emitter voltage of Tr1 is denoted as VA, voltage VC applied to sensor part 51 is the difference between VA and voltage VB dropping across circuit 6. This circuit 6 can have stable constant-current characteristics even in a low-voltage range by using FET1. Voltage VA, on the other hand, should be higher than the sum of voltage VC and the voltage that circuit 6 requires, but the voltage of circuit 6 can be made extremely low, so that voltage VA can be reduced extremely. |
