Active Filters for 1 MHz Power Circuits Under Strict Ripple Limitations

Recent advances in MOSFET technology have moved the switching frequencies of power circuits into the mega-Hertz range. The drive to these higher switching frequencies is motivated entirely by the smaller energy storage elements that supposedly result. Unfortunately, at these very high frequencies, the allowable ripple levels on the input and output of the power circuits are often much lower than they are at lower frequencies. This then requires greater ripple attenuation which means that all of the desired energy storage reduction cannot be achieved. As switching frequencies are pushed higher, the passive filtration elements often come to dominate the size and cost of the converter. In many cases, however, some of the large, costly, passive filter elements can be replaced with small, simple, active circuits. The result is savings in cost, size, and weight, of the overall filter. It is the purpose of this thesis to outline these cases and develope these active circuits. The thesis first describes the situations in which these active filters find their greatest import. It then moves on to developing the theory and evaluation criteria surrounding these filters. After discussing in depth, the various filter topologies, and available active devices, it presents a working circuit which was constructed in the lab. The performance of this circuit agrees quite closely with both theory and simulation, verifying all of the previous analysis. Thesis Supervisor: Dr. Martin F. Schlecht Title: Assistant Professor of Electrical Engineering