Spice-Modelling, Analysis and Measurement of a Current Programmed DC-DC Regulator

A buck-type converter is modeled for continuos conduction mode, simulated, analysed and measured with emphasis on loop gain to be able to design for stability. As a result of this "Structured Analog Design" process, a new SPICE2 model for current-mode programming plus a useful formula for control voltage to output voltage transfer function has been derived. The theoretical background is based on Dr. R. D. Middlebrooks papers on the subject, (2,3). In a case study, both prediction and measurement show a second pole, in loop gain, at a surprisingly low frequency. This implies that the current-mode control, although it seems to be the best method for regulation, must be properly understood for avoiding oscillating units.