| 摘要 |
<p>PURPOSE:To increase a voltage ratio to variation in impedance by providing a boosting circuit which inputs a voltage between power source terminals at the time of low impedance and boosts and supplies the input voltage to a detection part as a driving voltage. CONSTITUTION:A power source which has high impedance is connected between external power source terminals 10a and 10b. When no body is detected, a switch 13 is OFF and high impedance is obtained between the terminals 10a and 10b. The voltage between the terminals 10a and 10b is therefore in a high- voltage state. At this time, a sensor part 15 is applied with the voltage generated by boosting the voltage across a Zener diode 11 at all times and driven with this voltage. Here, when the sensor part 15 detects a body, the switch 13 turns on to short-circuit a resistance 12. Consequently, the voltage between the terminals 10a and 10b becomes a Zener voltage. This Zener voltage can be made lower than the lowest operating voltage of the sensor part 15. Therefore, a more secure detection output can be obtained.</p> |
