Power PSo C 120 Power Converters Discontinuous Current

Power PSo. C 120: Power Converter’s Discontinuous Current Mode Operation

Course Outline Section 1: Introduction Section 2: Origin of discontinuous conduction mode Section 3: Analysis of voltage conversion ratios

Course Objectives At the end of this course, you should be able to: Understand what discontinuous conduction mode is Understand how properties of converters change when this mode is entered Understand the techniques for solution of the converter waveforms and output voltage

1 Introduction

Introduction • Discontinuous Conduction Mode (DCM) is commonly observed in DC-DC converters • DCM arises when the inductor current reduces to zero and tries to reverse • Properties of converters radically change in DCM • Conversion ratio becomes load dependent and load voltage regulation becomes inadequate

2 Origin of discontinuous conduction mode Power Converter Circuit Elements

Origin of DCM

Origin of DCM

Boundary conditions I > i. L CCM: I > i. L DCM: I < i. L

Boundary conditions

3 Analysis of voltage conversion ratios Operating Principle

Conversion Ratio

Conversion Ratio • Inductor volt-sec and capacitor charge balance still hold

Conversion Ratio • Inductor volt-sec balance

Conversion Ratio • Capacitor charge balance

Conversion Ratio

Course Summary Explained what a DCM is Parasitics contribute to power losses in converters Analyzed the conversion ratio for the buck converter in DCM

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