Switch Mode Power Supplies with Idealised Performance

This presentation discusses the requirements of the Switch Mode Power Supplies (SMPS) employed by British Telecom for their System X telephone exchanges. The power plant is of the non-distributed type and the requirement is for rectified power packaged in light weight small dimensioned rectifier modules where the techniques of switch mode are ideally suited. Standardised modules rated at 28 amperes at 54.5 volts and weighing no more than 13.5kg are employed. Five rectifier modules connected in parallel are located in a Power Equipment Rack (PER) and PER's may be paralleled as required to meet the demands of the telephone exchange. SMPS rectifiers are notorious for drawing highly distorted currents from the supply installation and for producing interference in the radio frequency band due to the switching techniques employed. The SMPS rectifier described has a sinusoidal ac input current and avoids pollution of the ac supply and the environment.