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Old 6th December 2011, 01:38 AM   #1
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Default Crossover distortion in push-pull

I would like to use irfp140 and irfp9140 build a push-pull circuit, but I found very different Vgs, one is 4v, one is 5V, even at a bias circuit, how to ensure the two can also micro-conduction?
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Old 6th December 2011, 01:45 AM   #2
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Use a Vbe multiplier for the bias.
I have designed a few class AB amps using IRFP240/9240 and they sound very good.

I usually use an LTP with current mirror (with dc offset pot) and constant current source.
Into a VAS with Vbe multiplier with constant current source.
This will drive 2 or 4 mosfets.

Last edited by nigelwright7557; 6th December 2011 at 01:50 AM.
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Old 6th December 2011, 02:13 AM   #3
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If I use the regulator(eg 1n4730a) is feasible?
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Old 6th December 2011, 02:16 AM   #4
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A regulator keeps the voltage the same so could cause thermal runaway.

A Vbe multiplier with the transistor on the heatsink is a better solution.
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Old 6th December 2011, 04:05 AM   #5
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I found
irfp140N Qgs = 94nc @ Id = 16A, Vds = 80V, Vgs = 10V
irfp240 Qgs = 70nc @ Id = 18A, Vds = 160V, Vgs = 10V
If I was Vds = 20V case, is not irfp240 of Qg will be more smaller
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Old 6th December 2011, 12:17 PM   #6
AndrewT is offline AndrewT  Scotland
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Vgs values of 10Vgs to 20Vgs is near saturation level and near destruction level.

Note also the junction peak dissipation 1280Wpk for the 140N and 2880Wpk for the 240.
How fast will the junction heat up?
How long can that power pulse last before you damage the device?

I don't think you are looking at the correct data for your application.
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Old 6th December 2011, 02:38 PM   #7
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I said Vds, rather than the Vgs, you sure did it wrong!

Last edited by LoveVirus; 6th December 2011 at 02:43 PM. Reason: Wrong
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Old 6th December 2011, 03:01 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
Vgs values of 10Vgs to 20Vgs is near saturation level and near destruction level.
you clearly show Vgs = 10Vgs
Quote:
irfp140N Qgs = 94nc @ Id = 16A, Vds = 80V, Vgs = 10V
What have I surely got wrong?
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Old 6th December 2011, 03:26 PM   #9
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Quote:
Originally Posted by LoveVirus View Post
I found
irfp140N Qgs = 94nc @ Id = 16A, Vds = 80V, Vgs = 10V
irfp240 Qgs = 70nc @ Id = 18A, Vds = 160V, Vgs = 10V
If I was Vds = 20V case, is not irfp240 of Qg will be more smaller
irfp140N Qgs=94nc@Vds=80V
irfp240 Qgs=70nc@Vds=160

irfp240 Qgs=?@Vds=80V

What I mean is the parameter manual to different conditions, may mislead some of our judgments。
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Old 6th December 2011, 03:34 PM   #10
AndrewT is offline AndrewT  Scotland
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if that data is important to your use, then look up the graph that shows how the lead capacitances change with voltage.
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