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June 04, 2001

Right-Half-Plane-Zero (RHPZ)

Question:How do you compensate for a right-half-plane-zero (RHPZ)?

Original Question: I was looking for some tutorials on compensating for right-half-plane-zero. All designs I have done or seen (and the people I talked to) are buck topologies only, but I realize there are plenty of other topologies out there too. Perhaps you might find time in your busy schedule to cover the topic of boost converters that cover this right half-plane-zero (RHPZ) stuff without all the "bad" math that normally accompanies many college texts (if that's possible). I haven't seen this on your site yet (maybe I missed it if it is there). Just a thought. R. J. 05/31/01

Answer: I plan to eventually cover right-half-plane zeroes in my tutorial.

In the meantime, you may want to read "Loop Gain Crossover Frequency" by Dr. Ray Ridley (part of his Designer's Series) in the January 2001 issue (Volume 2, Issue 1) of Switching Power Magazine. The article discusses the RHPZ in the main body of the article and has a box giving a short tutorial on the RHPZ. A subscription to the magazine is free and you can subscribe on the Ridley Engineering website. (Ridley Engineering has been a past sponsor of the SMPS Technology website.) The article notes that the more ripple your supply has, the easier it is to compensate for the RHPZ. This is something that I did not realize until I read his article and attended his presentation at the ON Semiconductor seminar.

Typically I look for the best article on each topic. Until I find a better one, the Ridley article will be it for right-half-plane zeroes. Get a copy and put it in your professional library.

Posted by Jerrold Foutz at June 4, 2001 09:33 AM