Crossover distortion in push-pull

LoveVirus · 6th December 2011, 12:38 AM

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？

nigelwright7557 · 12:50 AM

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.

LoveVirus · 6th December 2011, 01:13 AM

If I use the regulator（eg 1n4730a） is feasible？

nigelwright7557 · 6th December 2011, 01:16 AM

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.

LoveVirus · 6th December 2011, 03:05 AM

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

AndrewT · 6th December 2011, 11:17 AM

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.

LoveVirus · 01:43 PM

I said Vds, rather than the Vgs, you sure did it wrong!

AndrewT · 6th December 2011, 02:01 PM

Quote:

Originally Posted by AndrewT

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?

LoveVirus · 6th December 2011, 02:26 PM

Quote:

Originally Posted by LoveVirus

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。

AndrewT · 6th December 2011, 02:34 PM

if that data is important to your use, then look up the graph that shows how the lead capacitances change with voltage.

6th December 2011, 12:38 AM	#1
LoveVirus diyAudio Member Join Date: Jul 2010	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？

6th December 2011, 12:45 AM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	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. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software. Last edited by nigelwright7557; 6th December 2011 at 12:50 AM.

6th December 2011, 01:16 AM	#4
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	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. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

6th December 2011, 11:17 AM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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. __________________ regards Andrew T.

6th December 2011, 01:38 PM	#7
LoveVirus diyAudio Member Join Date: Jul 2010	I said Vds, rather than the Vgs, you sure did it wrong! Last edited by LoveVirus; 6th December 2011 at 01:43 PM. Reason: Wrong


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6th December 2011, 01:13 AM	#3
LoveVirus diyAudio Member Join Date: Jul 2010	If I use the regulator（eg 1n4730a） is feasible？

6th December 2011, 03:05 AM	#5
LoveVirus diyAudio Member Join Date: Jul 2010	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

6th December 2011, 02:34 PM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	if that data is important to your use, then look up the graph that shows how the lead capacitances change with voltage. __________________ regards Andrew T.

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