Passive snubbers using RC, RL and sometimes RLC, are the simplest types of snubbers. An RC snubber, or damping network as it is sometimes called, consisting of a series R and C is by far the most common. One would think that designing such a snubber would be easy but to do it analytically turns out to be not so simple.
Rudy Severns, author of Snubber Circuits for Power for Power Electronics, talks on video about the importance of the series resistor-capacitor snubber network described in Chapter 3, Passive Snubbers, of his book.
You may not have the bandwidth to see the video, so a much shorter audio file and a transcript are provided.
(3:28)
Audio - RC Snubbers
Listen to the audio of RC Snubber Design (432 kB)
Transcript - RC Snubbers
Introduction
Hello, I'm Rudy Severns, welcome to my office. I'm writing a book on the design of snubber circuits for power electronics. In fact, the book's title will be Snubber Circuits for Power Electronics.
What I'd like to do now is to share with you the contents of one of the chapters so you can get a really good feel for what this book is all about.
R-C Snubbers
Now, one of the most common types of snubber circuits that is used is a simple RC series resistor capacitor-damping network. The reason this is so popular is the fact that any practical switching network; power converter, motor driver, whatever piece of power electronic equipment you have, in addition to the desired components; resistors, capacitors, and switches, and things of this nature, will also, because of its physical size, have lots of parasitic inductances and capacitances. So that when you have a rapid switching transition, you invariably, in a bare circuit, will get a lot of noise and ringing on the wave forms, and it's usually high frequency ringing. Sometimes it's up in the range of ten to even 50 megahertz.
It's very, very common to see all this noise and garbage on the waveforms. The RC damping network is a primary tool to eliminate or greatly reduce all of this type of ringing and it deserves a chapter all on its own.
It turns out that there are two subjects you have to treat. First of all, you have to look at what is the source of the ringing, why is it occurring? So you have to go ahead and model the circuit and put the parasitics in and explain, "Hey, this is why you have this noise and ringing."
Then you have to demonstrate what the effect is of adding RC damping networks at various points in the network. What you'll discover is, is that normally you have multiple parasitic inductances and multiple parasitic capacitances and it's ringing in multiple different ways.
So the purpose of this chapter is to clearly point all that out. To show you where you can put the damping networks in and what effect they'll have, and finally, of course, is to actually design the RC damping network and to recognize, that with RC damping networks, there's always an optimum value of resistance to give you the most damping. Make it too large or too small and your damping is not as effective for the given size of series capacitor.
So the RC damping network is very, very popular and needed. In fact, even when we go to dissipative snubbers whether using diodes or we go to energy recovery snubbers, even those circuits, they will require the use of these RC damping networks. This is a very important chapter.
Rudy Severns' book "Snubber Circuits for Power Electronics" is available for purchase on the Internet as an ebook in PDF format. More about the snubber ebook.
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