アプリケーションノート 942

消費電流が僅か6µAの負荷スイッチャ


要約: この回路はICの大変低い消費電流を生かし、±1mV以上の小信号で比較的大きな負荷電流の切替えができるようにします。

Figure 1's circuit draws only 6µA, but it enables a small signal of ±1mV or more to switch relatively large load currents. It takes advantage of the IC's very low quiescent current—1.2µA (max) per amplifier (less than a typical battery's self-discharge)—which is able to flow through R1 without turning on Q1. When operated with a sensing coil (as shown) and stimulated by a magnet, the circuit performs the function of a reed switch, but with greater sensitivity. Other applications include alarm systems, bipolar threshold sensing, and audio volume switching.

Figure 1. This load switcher enables a small signal to turn on a much larger load current.
Figure 1. This load switcher enables a small signal to turn on a much larger load current.

Inducing a signal of either polarity in the coil (by passing a magnet near it, for example) causes the dual op amp to draw more current from its VCC terminal. The increase produces a voltage across R1 that exceeds Q1's VBE threshold, activating the complementary monostable multivibrator consisting of Q1, Q2, and associated components. As a result, Q1 connects battery voltage to the load. For many applications, you can replace the monostable with a simple pnp output stage.

A similar idea appeared in the July 4, 1996 issue of EDN.


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APP 942:
アプリケーションノート 942,AN942, AN 942, APP942, Appnote942, Appnote 942