Download Electronics in Motion and Conversion December 2015

TECHNOLOGY
CONTENT
Note that even though we have 70 degrees of phase margin, due to
the low gain margin, we still have large undershoot and ringing. We
must stress at this juncture that, this is only a simulation and a digital
power supply in real life, with this specification, will almost certainly
be completely unstable for many different reasons.
Concluding Remarks
In this article, we discussed why we feel that a PID controller is not
best suited for stabilising most switch mode power supplies. We
supported our hypothesis with transfer function analysis, and various
simulations in both frequency and time domain. We believe that
switch mode power supplies are best designed in frequency domain
and presented the main downfall of PID as the need to heuristically
adjust the gain terms in time domain.
Bibliography
[1] “The Dark Side of Loop Control Theory” by C. Basso, APEC
21011
http://cbasso.pagesperso-orange.fr/Downloads/PPTs/Chris%20
Basso%20APEC%20seminar%202012.pdf
[2] “Switching Power Supplies A - Z, Second Edition 2nd Edition” by
Sanjay Maniktala ISBN-13: 978-0123865335
[3] Biricha Digital’s “Analog PSU Design Workshop” Handbook
[4] Biricha Digital’s “Digital PSU Design Workshop” Handbook
For the PDF version and related videos please visit:
www.biricha.com/bodo2D
PID controllers are excellent for thousands of applications; millions
are in use right now, but in our opinion there are superior alternatives
to PID for compensating switch mode power supplies.
Things to Try
1 -Download a copy of Biricha WDS PSU Design software from
www.biricha.com
2 -Attend one of our Analog or Digital Power Supply Design workshops
Vroom, Vroom. Beep, Beep
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HiTemp
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www.knowlescapacitors.com
www.bodospower.com
December 2015
Bodo´s Power Systems®
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