Improved switched mode electronic dimmer with sinusoidal voltage output

Abstract

Phase Control, the principle underlying the dimmers we use today, has been around for more than sixty years. During that time it has been implemented with a range of electronic switching devices. Phase control dimming is accomplished by turning on the electronic switch for only a selected portion of each cycle of the supply current. None of the switches was robust enough to turn off the current once it had started to flow, and therefore dimming was achieved by waiting for the required point in each power cycle before switching on. It is this sudden switching of the current, part way through the power cycle, which is the problem with phase control dimmers. The rapid change in current produced by switching the line, generates substantial radio frequency electromagnetic interference (EMI) and harmonic distortions in the power line. The EMI is radiated out from every dimmer, cable and luminaire in the rig. This can create interference with the lighting and sound control systems, radio microphones, in-ear monitoring systems, cell phones and even the listening assistance system. Harmonic distortions in the power line cause vibration and acoustic noise in dimmers, rattling lamp filaments, interference in audio, video and computer-based equipment, overheated neutral conductors; they may also damage service transformers. Based on a previous design, this project aims at improving the performance of a switched mode electronic dimmer which generates a controllable sinusoidal output voltage to the loads and hence eliminating the harmonic problem. Aspects of the switching losses, core losses and voltage drop etc are to be examined so that optimal design can be performed.