Sneak Circuits of Power Electronic Converters

Chapter 3Sneak Circuits of DC-DC Converters

3.1 Introduction

Basic DC-DC converters, such as Buck, Boost, and so on, are generally modeled and analyzed in two distinct operating modes, continuous conduction mode (CCM) and discontinuous conduction mode (DCM), based on the inductor current [1, 2]. In practice, a DC-DC converter is normally designed to operate in one mode to meet certain control functions by selecting the converter parameters (for example, the inductance) in advance. Sometimes the converter will not operate in the desired mode, for example, CCM will switch to DCM, and vice versa. Since the change of operation mode is caused by variation of circuit parameters, such as input voltage, load, or duty ratio, if CCM is regarded as the normal operating mode, then DCM can be considered as the sneak circuit mode of DC-DC converters, according to the definition of the sneak circuit.

In this chapter, six non-isolated DC-DC converters will be analyzed in detail, whereas Sections 3.2, 3.3, 3.4 will study the sneak circuit phenomena and their appearing conditions of the low-order DC-DC converters, which are Buck, Boost, and Buck-boost converters; and Cúk, Sepic, and Zeta converters which belong to the high-order DC-DC converters, will be discussed in Sections 3.6, 3.7, 3.8.

3.2 Buck Converter

3.2.1 CCM of Buck Converter

The schematic diagram of a Buck converter is sketched in Figure 3.1. When a Buck converter operates in CCM, the inductor current flows continuously and is ...