067-Switchmode Buck Power Converter Using Current-Mode Control

By: Raymond L. Barrett, Jr., PhD, PE

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Course Objective

This continuing education course is written specifically for professional engineers with the objective of relating to and enhancing the practice of engineering.

Course Description

067-Switchmode Buck Power Converter Using Current-Mode Control

The Switchmode Buck converter is used widely for high efficiency conversion of DC power available at a higher voltage and delivered to a load at a lower voltage. This course develops models of the Buck converter with current-mode control. Basic operation, a practical set of examples, and large/small signal models are discussed. The considerations for feedback regulation and load-current limiting control of the converter are introduced.

The selection of appropriate inductor and capacitor values are discussed, considering the frequency of operation and other design parameters. A constant-frequency Pulse-Width Modulator (PWM) controller is employed for pulse-by-pulse peak-current control. And a method for constructive use of inductor parasitics is employed for current monitoring. We introduce the peak-threshold current control in the open-loop model to illustrate a current-limit function, and then develop that control into the pulse-by-pulse current-mode control for voltage feedback. We develop the feedback conditions for frequency-domain, small-signal, stability in the open-loop model and include a Pole-Zero (PZ) compensator for good margins. We introduce the Zero-Order-Hold (ZOH) effects of the inherent sampling caused by cycle-by-cycle control and include those effects in the (PZ) compensator. The loop is closed and a "soft-start" capability added to avoid current-limiting during startup. Line and load regulation is shown for the example as well as transient load recovery. Finally, the need for "Slope Compensation" in some designs is discussed and a means for adding it is shown.

Questions about this course? Email the Author: raybarrett@comcast.net

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(4) 7 Reviews

067-Switchmode Buck Power Converter Using Current-Mode Control

James McLamara

04/10/2020

Verified Buyer

Excellent review having had 18 years of experience designing power supplies and the associated controls. I can imagine though this course might be challenging for someone not familiar with power conversion, modulator design, and classical controls theory.

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067-Switchmode Buck Power Converter Using Current-Mode Control

David S Kirsch

08/21/2019

Verified Buyer

I find the introductory material overly explained then later more interesting frequency domain stability material not described in sufficient detail (for me) for a thorough understanding. Consider this question(T/F); "Current-mode control signals can be obtained from the inductor parasitic ESR". . . .

Portions of the reviewers comments have been removed because they inaccurately discuss the correct answers to test questions

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067-Switchmode Buck Power Converter Using Current-Mode Control

Michael Madigan

10/24/2018

Good coverage of CM buck converters. The compensator value selection appears to be arbitrary, resulting in poles and zeros that happen to work. However, it is best to pick the p-z frequencies first in order to fit performance limits, then find the R's & C's to do the job.

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067-Switchmode Buck Power Converter Using Current-Mode Control

Paul Banaszak

10/18/2017

Verified Buyer

A lot of reading between the lines and induction required to answer test questions. Very challenging.

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067-Switchmode Buck Power Converter Using Current-Mode Control

Don Edwards

12/24/2016

Verified Buyer

Technical, but good. Some of the questions could be phrased better; they require close reading.

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067-Switchmode Buck Power Converter Using Current-Mode Control

Don Edwards

12/24/2016

Verified Buyer

Very technical but very good. The wording of some of the questions require close reading.

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067

Richard Neumann

02/09/2011

The course provided a good description of how this type of power supply worked. The description of the feedback system was thorough, but it was hard going for me since it has been a long time since I was involved with this. I would have liked to see a bit more on the hardward used to implement the control cycle.

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Course Code: 100206-04

Course PDH Hours: 4

Engineering Course Approvals

This course is accepted for engineering continuing education credit in all US states, territories, the District of Columbia, and Canadian provinces.
Ohio rules allow only 6-hours of unsupervised online courses such as this course per license renewal period
Kansas rules allow only 5-hours of self-study courses such as this course per license renewal period

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