Sensors & Transducers Journal

    (ISSN 1726- 5479)

Vol. 83, Issue 9, September 2007, pp.1574-1579

Design of a Opto-Isolator Circuit for Analogue DC Signal

S. C. BERA, ^*B. CHAKRABORTY

Instrumentation Engineering Section, University College of Technology

University of Calcutta, 92, A.P.C.Road, Kolkata-700009

^*Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, West Bengal, India

E-mail: baduchak@yahoo.co.in

Abstract: The opto - isolator is a device used to isolate a measured signal of a high voltage system from the of a low voltage system and vice versa. The conventional opto-isolator circuits are designed on the photo diode and the phototransistor based networks. The circuits generally have either high or low output depending on the magnitude of the input signal. Hence they are generally used for isolation of the digital signals. But these opto-isolator circuits are not suitable for direct isolation of the analog signal. There are few opto-FET type circuits, which may be used for this purpose. In the present paper the design of a very low cost LED - LDR based opto - isolator circuit has been described in order to isolate the analogue signal in the range from 0 - 5 volts dc. The function of the circuit has been experimentally tested and the experimental report is presented in the paper. It has been found that the output signal directly proportional to the input signal or of the same magnitude as the input signal may be obtained by the unit. Thus the direct isolation of a low voltage instrumentation analogue signal from a high voltage output device has been possible.

Keywords: DC Opto-isolator, Analog signal, Light depending resistor

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