| 摘要 |
<p>Light-sensitive switch structure for and method of turning a street light or other load on or off in response to variations in light level. The switch is designed to recognize a specific sequence of daily variations in light level and is capable of switching a load off at a light level lower than that at which the load is switched on. In a preferred embodiment, the switch consists of a photo-sensitive element, two operational amplifiers, a relay with its associated driver circuit, and a number of resistors forming voltage dividers. In accordance with the method of the invention, the photo-sensitive element, together with a resistor, establishes a signal voltage which varies in relation to the light level. Other resistors form voltage dividers which establish reference voltage levels at which desired switching is to occur. The operational amplifiers perform comparisons between the signal voltage and reference voltages and switch accordingly. One amplifier operates the relay which controls the load while the other biases the signal voltage to achieve the desired inverse operation. The stability of both amplifiers is insured by using feedback resistors to provide hysteresis, and a time delay circuit, consisting of a resistor and a capacitor to prevent sudden changes in the signal voltage. In other embodiments, two relays are used, one to control the load and the other to increase or decrease, by means of resistors, the currents through the operating coils of the relays to achieve the desired inverse off/on operation.</p> |
