Patent ID: 7791323

Claim:
A DC-DC converter comprising a switching circuit adapted to convert an input DC voltage to produce a voltage having a repetitively varying waveform, a first low-pass filter circuit adapted to smooth said voltage produced by said switching circuit, with said first low-pass filter circuit comprising a capacitor, and a control circuit adapted to apply feedback control to said switching circuit based on an output voltage produced from said first low-pass filter circuit, to maintain said output voltage at a predetermined target value, wherein: said DC-DC converter comprises a second low-pass filter circuit comprising a capacitor, adapted to smooth said output voltage produced from said first low-pass filter circuit for thereby producing a smoothed output DC voltage of said DC-DC converter; and said capacitor of said first low-pass filter circuit is selected to have a value of ESR (equivalent series resistance) sufficiently large that said control circuit operates with a phase margin exceeding a predetermined value, said phase margin being specified with respect to a frequency at which a loop gain of said control circuit becomes zero; and said capacitor of said second low-pass filter circuit is selected to have a value of ESR that is less than said value of ESR of said capacitor of said first low-pass filter circuit, whereby said second low-pass filter circuit achieves a higher degree of ripple exclusion than is achieved by said first low-pass filter circuit.