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Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Quick question: will my 30n60 igbts work on class e sstc operation? Based on the rise/fall times, you could push them to 8.7Mhz if they where always rising/falling. In drsstc application they are low frequency because of the large currents and resonant loads. Because in sstc operation they are handling much lower voltages and currents(but they are still 0 switching) I would think I could use them in my class e 800khz coil. Can someone second this?
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
I would never run mosfets at 8.7Mhz let alone igbts! My coil is 800khz, all I was saying was that in greater than perfect conditions, they are rated at 24nS rise/90nS fall.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
t=1/f so the time for one cycle at 800khz is 1.25uS so with a rise of 24ns and fall of 90ns it would be pushing it but it could work. you might have to drive them directly (with to-220-5, ixdd614ci).to get the frequency up. your driver will generate a lot of heat so it would need to be heat synced. if you used a fet with a low on resistance it would be better, less than half an ohm. there also must be schematics that have self feed back for class E
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
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Posts: 600
My design is close to Steve wards class e. my choices are between these igbt's and a fet with a 600v 4a rating. Rise and fall are 25nS, and the on resistance is 1.1 something... I don't have the data sheet on hand, but I think it's 1.1ohms... Little high wouldn't you say?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
if you use class E it is expected that high voltages will develop between your C-E junction when the device turns off. Using a 600 volt device meens that you may have to keep an eye on it. if you had a 1200v device you may be better off. you could use about 500v worth of TVS's to help protect it.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Richie tried IGBTs in his Class-E coil and... they asploded big time.
They have got somewhat faster, but I still don't see 8MHz being achievable.
The turnoff delay in a MOSFET is caused by capacitance, so the energy in it can be recovered by resonating the capacitance, and that's what Class-E amps do. But the turnoff delay in an IGBT is caused by minority carrier lifetime, which is a lossy mechanism, eating real power. You can't resonate a resistor.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Ahh!!! For the third time... Take that frequency, divide it by 10, then do the math! The frequency is 800 KHz no faster maybe slower. And for the voltage, Steve had 500v irfp460's although they where avalanche.
.0008GHz .8MHz 800KHz 800000Hz
Edit: one more thing, the bridge voltage is 50-70v maximum, so I don't think the voltage will spike over 4x anyways.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Here was my try with some 60 amp 600v IGBTs: The freq was about 600KHz and the small heatsink stayed around 105 degrees. You can see the heatsink in the video. I later tried 120v still with no over-voltage protection and the IGBT never sploded.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
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Posts: 600
Thanks arcstarter. But could you put the part code for your igbt's? My coil is very similar, and I would just like to look at the specs on your igbts. By the way, I feel your pain... I saw the comments on your video from mrgaleria.... Anyways, when I am done with this coil(probably tomorrow or Saturday, I will be sure to post the results!
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Igbts in an sstc
