An Automatic Mains Voltage Switch Protector for Domestic Appliances

摘要

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