Small-capacitance nondissipative ripple filters for DC supplies

Two configurations of ripple filters, one passive and one active, used to filter the output ripple of dc-to-dc converters and other power supplies are discussed. The passive one uses a small-microfarad capacitor and a mutual inductor; the active one uses these same components and, in addition, an operational amplifier. These filters have potential for spacecraft applications to enable the designer to use more reliable types of capacitors such as ceramic or mica instead of tantalum capacitors now commonly used in the conventional -section or pure-capacitance filters requiring large-microfarad capacitance. The passive filter has achieved attenuation greater than 40 dB and the active filter greater than 50 dB. Both of these filters accomplished significant capacitance reduction when compared with an -section filter for the same application.