| 摘要 |
<p>A circuit for detecting when the voltage between a pair of supply conductors (1,2) rises above a first predetermined level and subsequently falls below a second predetermined level comprises a pair of emitter-coupled transistors (3,4) supplied from the conductors. The base of one transistor (3) is fed with a constant voltage relative to one supply conductor (1) by means of a Zener diode (9) and the base of the other transistor (4) is fed from the collector of the one transistor to give a hysteresis effect via a voltage divider (11,12,13). The arrangement has two states in each of which one transistor is on and the other is off, which transistors these are signifying the relevant state. The arrangement changes state when the supply voltage rises above the first predetermined level and when it subsequently falls below the second predetermined level.</p> |
