Active filters for 1 MHz power circuits with strict input/output ripple requirements

As the switching frequency of a dc-dc converter is raised from 100 kHz to 1 MHz, one would expect the energy storage elements of the circuit to be correspondingly reduced in size. If the circuit must meet input and output ripple requirements of the nature of MIL-STD-461B CEO3, however, the advantage of a higher switching frequency is significantly offset by the higher filter attenuation levels required. This paper discusses the use of active filters, in conjunction with minimal passive filters, to achieve the required ripple levels with a much smaller overall volume. Working active filters with gains in excess of 100 at 1 MHz are also presented.