SSZTAY2 august   2016


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Bob Sheehan


Whenever you have a job to do, it’s important you have the right stuff, whether it’s knowledge, tools, supplies or equipment are at the basic list. In addition to working in power-supply design, I do a lot of hands-on projects, including automotive repair. Not because I’m cheap (well, maybe a little), but usually because I’m not satisfied with the job when someone else does it.

Recently, I got my motor home back from the transmission shop and noticed an oil leak. After a while the oil started pouring out from the cooler adapter seal. I knew the shop must have removed it to get other work done. After disassembling the filter and adapter, I found the petrified remains of the original gasket underneath. So much for a quality job. So I headed to the parts store for a gasket set. The replacement O-ring seemed a bit skimpy, and it leaked even worse. I went back to the parts store and the clerk said I needed to get the right stuff – some expensive form-a-gasket material that comes in a can. He handed me the can and there it was, right on the label: “The Right Stuff.” Ah ha. It worked great.

Doing a good job requires knowledge and expertise, which is why I have been a fan of today’s worldwide Power Supply Design Seminars since I first attended in the 1980s. Before Texas Instruments, Unitrode’s applications experts hosted the seminars. I remember attending as a young engineer and soaking up as much as I could. The best part was a chance to have lunch with one of the authors or presenters. I remember thinking, oh, if I could just be like those guys. So now I guess I am one of those guys.

While working for National Semiconductor prior to the TI acquisition, I developed a “Loop Compensation Made Easy” training course for our field applications engineers. Later, my colleague Louis Diana incorporated the presentation for TI training around North America, and for the 2016 seminar we have expanded the material to include isolated topologies in a topic titled, “Switch-Mode Power Converter Compensation Made Easy.”

There was one thing that always bothered me about frequency compensation for current-mode control. The simplified approach uses a single-pole approximation for the power stage and output filter, with the assumption that the inductor pole moves out to some higher frequency near the switching frequency. But where exactly does it go? After attending R.D. Middlebrook’s course, “New Structured Analog Design,” I was able to quantify the inductor pole simply using impedance analysis. If I lost you here, don’t worry. You don’t need to know how to derive the equations in order to understand and use the results you will learn in this year’s seminar.

By the way, our presentation has a list with links to compensator design topics within the entire Power Supply Design Seminar library by some of the greats – like Lloyd Dixon and Bob Mammano – along with more recent resources.  The library is open to all and can be accessed at

If you have a chance to attend the kick-off session in Boston, the original authors of the material typically make the presentations in that city. In addition to local and regional power experts, many of the authors will present at other locations; for example, I will be in Boston, Irvine, Seattle and San Jose. The schedule of topics and registration for the 2016 Power Supply Design Seminar, also known as SEM2200, is here: This year, we have a new format with two rooms: one for seminar topics and the other for demonstrations and related topics. I look forward to seeing you and am sure you will find the right stuff to help with your power designs.