Input filter design criteria for switching regulators using current-mode programming

摘要

Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H/sub S/, output admittance Y/sub s/, and the y-parameter model of the switching converter. The criteria are listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T, line-to-output transfer function A/sub gf/, and output impedance Z/sub of/ requirement is given, an input filter with H/sub s/ and Y/sub s/ can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H/sub s/>or=1 (may be relaxed to 3-6 dB), and Y/sub s/ is larger than the curves of the graphical illustration, perhaps using 6 dB as a rule-of-thumb minimum separation.