Transformer-coupled photodiode circuit for lightning and other light

Abstract

An efficient optical radiation detector for lightning or other light signals such as pulses, bursts, flashes, and steady fluctuations. A silicon photodiode (or similar light-sensitive silicon device) is arranged to receive light signals (infrared, visible, ultraviolet, broadband, etc.) of interest. The photodiode is connected across the primary winding of a properly-designed transformer. The transformer-coupled photodiode circuit gives AC coupling, photodiode bias, voltage gain, and several other desirable detector characteristics. Light fluctuations on the photodiode produce variations of photocurrent in the transformer primary circuit which, in turn, induce current in the secondary winding and circuit of the transformer. The current induced in the secondary circuit of the transformer is used to do useful work (such as energize an audible alarm, increment a counter, latch a relay, etc.) or it is further amplified and processed, or combined with other signals to make an event detector such as a lightning sensor. The transformer-coupled photodiode circuit provides a general purpose light-change detector that is particularly useful as the optical sensor element of a lightning detector including any of a variety of so-called 'lightning coincidence detectors'. The chance of a 'false' lightning detection is greatly reduced by the combination of an electric or magnetic field-change detection device with the transformer-coupled photodiode circuit.