| darkfenriz |
Hallo
is output imedance of IGBT low or high compared to bjt and MOSFET??
just starting interesting IGBTs and cannot find much practical data- only sructure theory.
waiting for answers
cheers |
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| Sch3mat1c |
AFAIK, it's a BJT with a MOSFET in front of it, sorta, so it doesn't take any power to switch massively. But that doesn't explain why they are slow, they only come up to 600V (at least what I've seen at Mouser) and supposedly have NO tolerance for anything out of limits.
Don't know what kind of linearity they have, if any. Only used for switching big stuffs AFAIK...
Tim |
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| hjelm |
Does this help?
600V 30A IGBP
You can derive the output impedance from the datasheet but the problem is that it is increasing at low Vce values, i think.
At 30A the Vce drop is ~2.1 v which is about 70mohm. |
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| darkfenriz |
thank you
i found somewhere this schematic (hope I don't harm enyone's copyright or anything) and was thinking of common emmiter or SE mode
what do you think? |
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| hjelm |
Building anything with IGBP devices is way over my head.
Although i do think the schematic is interesting especially the two feedback loops. I wouldn't consider myself competent enough to design those. |
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| darkfenriz |
another words
do you think IGBT may work good as a follower? |
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| johnnyx |
I have read that there are special considerations required to operate IGBT' as a follower, such as you see in many amp designs. They can latch-up, due to a parasitic NPNP thyristor style construction. I saw a design once, probably in Wireless World or Electronics World, that used a biasing arrangement to prevent this occuring.
OTOH JLL Hood has used them in amplifier designs, so maybe this problem is exagerated. I would do a bit more background reading first before trying them.
I see them used a lot in the latest power inverters for motor control. In that application, they appear to have many advantages, efficiency being the most obvious, in that the size has shrunk for the same power. :) |
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| hjelm |
Saw this on peufeu's site. Maybe some ideas?
It includes latchup protection.
IGBP amp |
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| johnnyx |
| That is very probably the one I was thinking of.:) |
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| darkfenriz |
I'm just looking for lowest output impedance possible
igbts seem tempting with low emmiter resistance combined with voltage driving, don't they? |
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| audiocrow |
The IGBT's are relatively slow because of is own geometry and type of construction. Insulated Gate means that the Gate it's insulated from the rest of the transistor using extra layers of oxide deposites. This extra oxide (relatively to mosfet smaller amount) increases the Gate capacitance ... and the rest I think it's quite clear : Extra-capacitance means higher charge time of the capacitor meaning higher switch time meaning a slow amplifier.
In terms of speed BJT tecnology it's major!
P.S. this was my 1st post...Portuguese greetings :) |
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