DC-DC converter utilizing respectively separate low-pass filters in feedback control and output voltage smoothing and method of designing the DC-DC converter
AssigneeDenso Corporation
InventorAtsunori Okubo
Life of this patent
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Abstract
A DC-DC converter includes a switching circuit controlled to convert an input DC voltage to a voltage having a repetitively varying waveform, a first low-pass filter circuit that includes a first capacitor and which smoothes the output voltage from the switching circuit, a control circuit applying feedback control to the switching circuit to regulate the output voltage from the first low-pass filter circuit, and a second low-pass filter circuit including a second capacitor, for smoothing the output voltage from the first low-pass filter circuit, with the second capacitor selected to have a lower value of equivalent series resistance than the first capacitor.
Claims6
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.
A method of designing a DC-DC converter, the 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,
- 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, and
- 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;
- wherein said method comprises steps of:
- selecting said capacitor of said first low-pass filter circuit 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,
- selecting said capacitor of said second low-pass filter circuit to have a value of ESR that is less than said ESR of said capacitor of said first low-pass filter circuit.
Dependencies are inferred from the claim text.