Operation of Optocouplers Under the Influence of Extreme Environmental Conditions

In the present paper, a detailed study was carried out concerning the factors affecting the performance of one of the most important optoelectronic devices that is optocouplers. In this concern, operation of such devices under the influence of extreme environmental conditions of input LED current (I _F) up to 120 mA and temperature (from –175 °C up to 100 °C) was investigated. A detailed experimental and simulation studies of the initial electrical characteristics of the input LED and output phototransistor of the proposed 4N25 optocoupler, as well as, its current transfer characteristics were investigated. Where, the obtained results from both techniques were found to be in a good agreement. For the input LED, and within the temperature range from –175 °C up to 100 °C, the threshold voltage was shown to be varies from 1.06 Volts down to 0.72 Volt, although its value at room temperature was 0.8 Volt. On the other hand, and considering the output phototransistor, its temperature dependence of the collector current was shown to follow a Gaussian distribution, where as an example, at input LED current of 10 mA, and emitter-collector voltage of V _CE = 0.6 V, the collector current value varies from 6.6 mA up to 10.5 mA within the investigated temperature range, with a peak value of 19.7 mA, recorded at –55 °C. Finally, for the current transfer characteristics, dc-current gain and current transfer ratio of the 4N25 optocoupler, their values were shown to be varied from 1.29 mA, 0.66 and 66% up to 10.28 mA, 1.05 and 105%, within the investigated temperature range, following a Gaussian distribution with a peak values of 14.1 mA, 1.97 and 190%, recorded at –55 °C, respectively.