Journal of Emerging Trends in Engineering and Applied Sciences: Research Areas

Abstract:
Electronic and electrical appliances used in most homes in the country are designed to operate at a nominal 230 V AC, which ought to be acceptable within certain tolerable upper and lower limits. Excessive fluctuations beyond these limits may cause the appliance to malfunction or get irreparably damaged. Most protective devices are imported as well as expensive. The circuit presented is a relatively cheap automatic mains voltage switch (AVS) protector that senses undesirable and harmful fluctuations in mains voltages and disconnects the appliance whenever the mains voltage supply goes above or below pre-settable and safe tolerable limits or 'window'. The appliance is automatically reconnected when mains power returns to normal within that 'window'. The design features anti-surge protection, a transformerless power supply for the circuitry, a window comparator for the detection of low and excessively high mains voltages to the load and a switching relay capable of switching high currents, ideal for compressor-based appliances. A delay section for control of spurious low voltage drops as well as mains stability is incorporated. The design provides a safe operating voltage range of 180V to 250V and offers practically the same functions as those of the imported brands. Basically, the design consists of various circuit building blocks and circuit techniques that would be of interest to the electronic hobbyist.

Keywords: transients, surge, over-voltage, window comparator, monostable, transformerless power supply.

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