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Old 8th March 2007, 12:33 PM   #11
Eva is offline Eva  Spain
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One more example of dissipation limited SOA: SKP10N60 IGBT. This is a TO-220 device which explains the much lower pulsed dissipation capabilities. BTW: This IGBT is one of those that is paralleling-friendly.
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Old 8th March 2007, 07:40 PM   #12
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Setting aside the availability of complementary parts, the
biggest issue is that the devices are really two stages, a
Mosfet driving a BJT, and you don't have access to the
junction of the Drain-Base. Ordinarily in a linear circuit you
would like to be able to bias the Mosfet at a higher current
than the Base current for the BJT for better linearity and
bandwidth.

Also, matching such devices for parallel linear operation is
more problematic, as there are more degrees of freedom
to the set point.

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Old 8th March 2007, 09:10 PM   #13
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How is it possible to make a BJT without second breakdown? Is it some kind of new technology? If so can this be applied to 'normal' BJTs?
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Old 8th March 2007, 09:31 PM   #14
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It is not like that, of course a N-IGBT works kind of similar to N-mosfet driving a PNP bjt, but these devices' thermal behaviours can vary.
For example some have positive Vce-sat thermal coefficeint, while others have negative, so some are easy to parralel while others aren't.
For audio amps they are rather not useful devices in my opinion, they might be more efficient at, say, 100kHz PWM and >1kW power. That's all, I won't believe they have some magic sonic character.
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Old 9th March 2007, 08:58 AM   #15
Eva is offline Eva  Spain
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Let's review some features of modern fast switching IGBT:

- High voltage (600V) and current (>20A) ratings.
- MOSFET-like SOA only limited by temperature and dissipation.
- High dissipation capabilities (200W typ. for TO-247 cases).
- Higher transconductance than MOSFET.
- Higher threshold voltage than MOSFET (4-6V, easier to drive).
- Almost three times lower gate charges and capacitances than MOSFET (again easier to drive).
- Fall times below 100ns providing 10 to 100 times higher bandwidth than audio power bipolar transistors.
- Inherently cheaper than MOSFET due to the much smaller amount of silicon employed to get the same current, voltage and power ratings.

Aren't IGBT the ideal output devices for high power audio where supply rails above +/-90V are required?

Obviously, for lower voltages like +/-50V the advantages over MOSFET or japanese Toshiba-like bipolars are not so clear.
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Old 9th March 2007, 09:08 AM   #16
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EVA,-here in India we have access to GT60 and CT60 900V 75A TO-264 IGBTs from Toshiba and Mitsubishi, but their SOA isn't much promising for linear applications...
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Old 9th March 2007, 11:10 AM   #17
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You are looking at the wrong type of IGBT. The ones that you mentioned are old-style IGBT for things such as induction cooking.

Check those two datasheets:

http://www.fairchildsemi.com/ds/SG/SGH80N60UF.pdf
http://www.infineon.com/upload/Docum...60_Rev2G_1.pdf
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Old 9th March 2007, 03:20 PM   #18
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Default Great Devices

The Infineon IGBT looks much more promising than the Fairchild one....I must try them as soon as possible....in my Class-TD Grounded Bridge amp with Monorail Tracking....

Eva,some people here wont try that type of Igbt, because their mindset is strucked into complementary designs....only..


Also the zero Temp coeff is around 35A for Vgs=7.4V..But I think the variation of Idd w.r.t to Vce is lesser as compared to mosfets....hence biasing wont change subsequently, unless one has to use a transconductance cell for each mosfet to keep the things stable....
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Old 9th March 2007, 04:00 PM   #19
Eva is offline Eva  Spain
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Quote:
Originally posted by Nelson Pass
Setting aside the availability of complementary parts, the
biggest issue is that the devices are really two stages, a
Mosfet driving a BJT, and you don't have access to the
junction of the Drain-Base. Ordinarily in a linear circuit you
would like to be able to bias the Mosfet at a higher current
than the Base current for the BJT for better linearity and
bandwidth.

That's not completely true. The "MOSFET driving BIPOLAR" tale is only a popular way of explaining IGBT behaviour to straight people. An IGBT is a device having a single die and an unique structure which combines the advantages of MOS "channel" effect and bipolar "charge storage" effect. The absence of second breakdown is a consequences of this combination.

The following document shows the internal layout of old and new generation IGBTs and compares them to MOSFET for high voltage switching applications:
http://www.irf.com/technical-info/wh...c03nptigbt.pdf
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Old 9th March 2007, 07:43 PM   #20
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That last post has really shed some light Eva, thanks. Up to now I took the same view as Nelson.
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