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High-power, high-voltage pulse power: The basics

by Timo Stehmann4. June 2013 20:01
In some applications pulse power supplies need to handle very high currents (>10kA) and voltages (>30kV). For many decades the only devices that could come close to the required specifications were vacuum tubes. These vacuum tubes are highly specialised and were graced with their own name: Thyratrons (see image below). These are amazing devices, capable of handling very high pulse currents at mind-blowing speeds (<100ns). Since no silicon is involved, these devices are very robust but they have a limited life-time. In the early days the only alternative to thyratrons were spark gaps. Spark gaps, even today, are very fast (<50ns) and are able to handle very high voltages. Unfortunately, the life-time of spark gaps are even more limited than thyratrons. However, if you want to generate very fast pulses the quick and dirty way, then spark gaps are the way to go. In our modern commercial world thyratrons have been become out-dated for many reasons. There is the limited life-time for one and then there are the commercial restrictions. Thyratrons were/are used for nuclear weapons as well and using them in commercial devices can be troublesome. What are the alternatives? [More]

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Power electronics | Power supplies | Pulse power

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Common cause of EMI in power electronics - the diode

by Timo Stehmann7. May 2013 16:47
If you were involved in some power electronic project you probably got involved in a discussion about power MOSFET drivers. More specific the one statement: "Listen, don't use that driver. It always latches up and acts weird. Rather use this fancy opto-isolated driver." Yes, that stupid driver! Bad driver! Do what all professionals do and use that opto-isolated driver!

I started becoming skeptical about this statement when one person mentioned an IR2102 as being one of those bad drivers. For those who don't know the driver: This is an International Rectifier high- and low-side driver rated for 600V. I never had problems with them. Why was it a problem now? The simple answer is that the latching drivers pointed out an inherent problem in the power supply. It was acting as a giant EMI emitter! Using fancy drivers just masked the problem. Sure, there are probably drivers out there that are too susceptible to EMI, but in general they are relatively robust. So, which component in a switch mode power supply can emit the most noise? The inductor? Maybe. The transformer? Mmmh, don't know. No, in many cases it is that reverse/free-wheeling diode! Yes, that one! More specifically the reverse recovery mechanism of the diode. [More]

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Power electronics

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