Design of a low-voltage low-power dc-dc HF converter

Abstract

Many portable electronic applications could benefit from a power converter able to achieve high efficiency across wide input and output voltage ranges at a small size. However, it is difficult for many conventional power converter designs to provide wide operation range while maintaining high efficiency, especially if both up-and-down voltage conversion is to be achieved. Furthermore, the bulk energy storage required at contemporary switching frequencies of a few megahertz and below limits the degree of miniaturization that can be achieved and hampers fast transient response. Therefore, design methods that reduce energy storage requirements and expand efficient operation range are desirable. This thesis focuses on the development of a High Frequency (HF) dc-dc SEPIC converter exploiting resonant switching and gating with fixed frequency control techniques to achieve these goals. The proposed approach provides high efficiency over very wide input and output voltage ranges and power levels. It also provides up-and-down conversion, and requires little energy storage which allows for excellent transient response. The proposed design strategies are discussed in the context of a prototype converter operating over wide input voltage (3.6 - 7.2V), output voltage (3 - 9V) and power (0.3 - 3W) ranges. The 20MHz converter prototype, utilizing commercial vertical MOSFETs, takes advantage of a quasi-resonant SEPIC topology and resonant gating technique to provide good efficiency across the wide operating ranges required. The converter efficiency stays above 80% across the entire input voltage range at the nominal output voltage. The closed-loop performance is demonstrated via an implementation of a PWM on-off control scheme, illustrating the salient characteristics in terms of additional control circuitry power dissipation and transient response.