Abstract—Electronic devices in industrial applications have to run under noisy environments. Especially, programmable logic controllers and microcontrollers need filtered inputs to avoid the noise and not to lead to any malfunctions. Any electronic device collecting signals from the surrounding environment must have an active or passive filter to reduce noise. Noise sources are varied and spread on the air or in the cables. Electromagnetic noise spreads on the power supply cables and in order to avoid the conducted noise, input signal must be filtered by filters centered at 50 or 60Hz. In addition to the filter, input signal voltage is in different levels than the microcontroller side. A simple way to change voltage level is to use optocouplers. But optocoupler must have adequately fast response time. Microcontroller operates at determined low voltages such as 5Volt or 3.3Volt. On the contrary, industrial signals have wide variations such as 12V or up to 60Volts DC according to application. In this study, a commercial patch circuit was designed for logical inputs targeting the microcontrollers, programmable logic controllers and similar devices running under the noisy industrial area. Proposed circuit includes a filter centered for 50Hz and 5Khz, optocoupler to provide isolation and current source and voltage divider to increase the logical stability. Because of the commercial target circuit was designed minimum numbers of components and built in only 0.73cm2 area. Proposed circuit isolates the signals and leads to robust running under the noisy environments for industrial devices.
 

Index Terms—optocoupler, transistor, microcontroller, isolated input, low pass filter, current source, programmable logic controller

Cite: Bayram Akdemir, Ahmet Afşin Kulaksız, and Şaban Öztürk, "A Novel Isolated Filter Built with One Transistor for Industrial Devices," International Journal of Electronics and Electrical Engineering, Vol. 4, No. 3, pp. 226-230, June 2016. doi: 10.18178/ijeee.4.3.226-230