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I am miniaturizing a circuit used to generate a pulse using condensers into an inductive load. I am a little lost on what would be the best type of component to choose to start the discharge (ie. a switch closing the circuit and allowing the condensers to discharge in the inductance).

What in your opinion would be the best component given these constraints:

  • Pulse width in the order of us (0.1 to 100us).
  • Pulse frequency of 10hz.
  • Component must be able to block at least 1000V.
  • Pulse current between 100Amps to 200Amps.
  • Size constrained: Less than a few inches for this particular component.
  • Can be expensive, but not in the hundreds of $.

Condensers are in the order of a few uF and the load is an inductance of between 50 to 300 uH and a few ohms.

So far I am thinking either Silicon Carbide MOSFETS (big and expensive but allow good control), or avalanche diodes like this one (cheap and small). Thyristors are what I am using rigth now but I am trying to get smaller and if possible cheaper. As far as I read, spark gaps and Gaz discharge tube tend to have a limited lifetime (which is not okay in my case).

Do you see any other alternative ? Did I miss something ?

Tony Stewart EE75
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user119911
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    For high voltages IGBT's are the answer, but 1Kv times 200 amps equals a few hundred dollars. I could be wrong, as prices for these modules come down every year. They are used in MRI machines and Mag-lev trains. Google IGBT and see where it leads. –  Aug 06 '16 at 02:33
  • Uh I am afraid IGBTs could hardly cope with 100ns pulsewidth. I'd rather go shopping for some SiC MOS they can be expensive but not that big. For around 50€ you should be able to get many TO-247 and even some SMD one. In a quick search I spot APT80SM120B 1.2kV 190A pulsed ID. – carloc Aug 06 '16 at 06:50
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    Flashlamp-triggered SCRs, "LASCRs" are the best way, I'm told, to get high dI/dt slews (and 200A and 0.1 us implies you need that). – Whit3rd Aug 06 '16 at 07:05
  • are you after a square pulse or would an exponential suffice? IGBT's are not suitable for this.. even 4th gen will switch only 100ns... –  Aug 06 '16 at 10:02
  • I don't really care about the shape of the pulse. Yes, I ordered this exact type of SiC MOSFET (APT80SM120B), will be trying them next week, but honestly I am still hunting for something smaller and/or cheaper. As far as I have seen, IGBTs do seem interresting, I discarded them earlier in the project but may be trying them soon then. The pulse width is important but the component's activation time is not really. – user119911 Aug 06 '16 at 12:35
  • IGBT's are good (majority of my inverters use them [mosfets, SCR for those other cases]). Its all about choosing the right device/s for the job. why is the voltage important? –  Aug 06 '16 at 19:28
  • I am also constrained in size also for the capacitors. Hence, if my capacitors don't change and my voltage goes lower, then I can't reach the currents I am set to acheive. Currently I feel that I may reach a kind of sweet spot around 1.2KV both taking in account the capacitor's size (ceramic 1.2KV, Knowles Syfer, 5 by 5.70 mm) and the switching technologies available. – user119911 Aug 06 '16 at 20:53
  • I can't imagine 100 Amps passing from a 3uF cap charged at 1kV to a 10uH inductor at 10 pps for only 100us. BUT I can expect a few mA. Schematic please? – Tony Stewart EE75 Sep 18 '16 at 02:41
  • Cree/wolfspeed has a few new sicfets worth looking at. C2M0045170D as an example. http://www.wolfspeed.com/media/downloads/886/C2M0045170D.pdf – steverino Nov 13 '16 at 06:12

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What you should do to get the cheapest usable IGBT's, is to buy a frequency inverter and disassemble it.

A frequency inverter is a device that powers electromotors. It creates three sinewaves build up of pulses. It operates with pulses up to 80 kHz, so a pulsewidth of 6 microsec should be no problem.

Voltages up to 500V= and current RMS up to 1kA, depending on the model: large inverters can power 500kW electromotors. So if you are willing to get your hands dirty, you can save money on your IGBT's!

Don't worry if you can find one to meet your specs: your pulse is just a slow 10Hz, maximum power 200 kW, judging from your specifications.

Your final question: Is there an alternative for IGBT's ? For your application, there is no better alternative!

Geert Jan
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