Design of a 22V∼32V-to-15V DC/DC Power Converter under Input and Load Variations

This report presents the design procedure of a buck converter, which converts a 22V∼32V DC input voltage to a 15V DC output, under a resistive load variation from 1.5Ω to 4.5Ω. Detailed analysis and simulation results, as well as electrical and thermal device specifications are provided. A voltage-mode PI controller is designed to stabilize the averaged system under input and load variations. The worst-case efficiency of this buck converter is above 94.59%. I. DESIGN REQUIREMENTS The design requirements of the electrical parameters for the buck converter are listed in Table I. TABLE I DESIGN REQUIREMENTS. Input voltage range 22 ∼ 32 V Input voltage transient limit 44 V for up to 1 ms Output power range 50 ∼ 150 V Output voltage (static) 15 V±3% Output voltage (transient) 15 V±20% Output voltage ripple (p-p value) ≤ 100 mV Input current ripple (p-p value, ideal source) ≤ 100 mA Efficiency ≥ 88% Besides, it is required that the junction temperature of the power devices should remain sufficiently (at least 25C) below the allowable maximum junction temperature, while the ambient temperature is in the range of −20◦C∼ +50C. It is also required that the temperature rise of inductor should be below 50C. II. TOP-LEVEL DESIGN VIEW As shown in Fig. 1, assume that the duty ratio of the switch is d and the input DC voltage is V1, then the output DC voltage can be decided as Vo = dV1. (1) And the power at the output stage is Po = V 2 o /Ro. (2) Since Vo = 15 V, and Po = 50 ∼ 150 W, the load resistance Ro can vary in the range of 1.5 ∼ 4.5Ω. And accordingly, the averaged current through the inductor shall vary in the range of 10 3 ∼ 10 A. In our design, we see V1 = 27 V and d = 59 as the nominal design. The switching frequency is set as fsw = 200 KHz based on the following tradeoffs: V 1 Ro Lo