Hi all,
In recent years, IR and Vishay IRF series power mosfets have been changing over to "N" suffix variants e.g. IRF 540N. I've seen this change described as offering the user better performance due to optimised switching behaviour. I read that as meaning smaller chips and lower manufacturing cost - a little spin on a common trend in semi. manufacture today 😉
My specific question is, for linear applications and small mosfets with a desirable high RDss like IRF530/9530 or IRF640/9640 at least, are there penalties to performance in their power handling, safety margin and distortion levels in typical audio power output applications?
In recent years, IR and Vishay IRF series power mosfets have been changing over to "N" suffix variants e.g. IRF 540N. I've seen this change described as offering the user better performance due to optimised switching behaviour. I read that as meaning smaller chips and lower manufacturing cost - a little spin on a common trend in semi. manufacture today 😉
My specific question is, for linear applications and small mosfets with a desirable high RDss like IRF530/9530 or IRF640/9640 at least, are there penalties to performance in their power handling, safety margin and distortion levels in typical audio power output applications?
I would say yes, the newer parts optimised for switching are more vulnerable to thermal run away in linear audio. The threshold voltage curves tend to show the zero temperature coefficient current is higher and the temperature coefficient at tens of mA is higher
I did a quick comparison between IRF540 and IRF540N and what stands out for me is a substantial loss of SoA with the -N variant. Look at the SoA line for 10mS pulse - notice its no longer parallel with the shorter pulse lines.
My conclusion is that the -Ns are hugely inferior as audio output devices.
My conclusion is that the -Ns are hugely inferior as audio output devices.
Yes the slope is doing a more bjt like plunge.
2A a 40V 10ms.
The old Vishay IRF540 managed just 1A at 40V 10ms, so not all IRF540s were equal.
You would need a lot of the Vishays in parallel for a decent drive into 4 Ohms
2A a 40V 10ms.
The old Vishay IRF540 managed just 1A at 40V 10ms, so not all IRF540s were equal.
You would need a lot of the Vishays in parallel for a decent drive into 4 Ohms
I use a lot of MOSFET IRF540 / 9540 and IRF640 / 9640 transistors. These are audio amplifiers that I produce and I can not tell you that I found a fundamental difference between IRF540NPBF and IRF540
It is very possible that differences will be found in Class D amplifiers
It is very possible that differences will be found in Class D amplifiers
Thank you all for the useful thoughts and information. I'll have a look over what can be done about a reduced SOA because my current design is already close to limits and parts stocks are running low. I guess my real fear is the pain of changing to more expensive and larger devices if necessary.....more testing 
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