does MOSFET need thermal compensation ?

djdamix · 8th February 2005, 05:12 PM

I've read that MOSFET need no thermal compensation since when their temperature rise, the current decrease. Does it means I can do without ??? (I use IRFP240 & 9240)

Thanks for any comment.
David

wimdehaan · 8th February 2005, 05:36 PM

MosFets like the IRF 240 and equiv. do need some kind of thermal compensation. Only Power Mosfets Like the BUZ900 / 2Sk1058 / 2SK135 do not need this. These devices do have a negative temperature coeficiente, and this will avoid thermal run-a-way.

djdamix · 8th February 2005, 05:41 PM

thanks for your input,
but it's irf"P"240 and IRF"P"9240, I think they are power devices ...

David

K-amps · 8th February 2005, 05:42 PM

Quote:

Originally posted by wimdehaan
MosFets like the IRF 240 and equiv. do need some kind of thermal compensation. Only Power Mosfets Like the BUZ900 / 2Sk1058 / 2SK135 do not need this. These devices do have a negative temperature coeficiente, and this will avoid thermal run-a-way.

Is there a generic name or classification of FET's with -ve temp coefficient or does one go through the datasheets of each device....

jacco vermeulen · 8th February 2005, 05:53 PM

You mean like a lateral or vertical Mosfet.

K-amps · 8th February 2005, 06:11 PM

Si Senor....

richie00boy · 8th February 2005, 06:14 PM

Indeed. IRF (any type) are vertical devices intended for switching and the -ve tempco only happens at quite high currents. Lateral MOSFETs are specifically for audio -- Hitachi, Exicon and Magnatec are the most prominent -- and these have -ve tempco starting in the milliamps range.

K-amps · 8th February 2005, 06:16 PM

Thank you Sir!

So Slone likes Laterals and Nelson likes vertical FETS... what gives?

jacco vermeulen · 8th February 2005, 07:39 PM

Mr Pass stated in one of his articles that he has a "dumpster" load of them, the main reason for his choice.
I think he referred to it as a stategic reserve, good thing he is not in the Silver business.
I have the impresion it was Mr Pass who made the vertical IRF's more accepted.

The main reason for lateral Hitachi Mosfet in the 80s and 90s was their availability, the ruggid TO3 package, low Ciss, and most of all their 'good' sound.
In those days verticals were generally considered a NoNo., even diy mags advised not to go for vertical mosfets.
Overhere companies as Silltech pushed the popularity of laterals, in Oz a company as Perreaux, in the US Conrad Johnson and some others.
I built a few amps designed for lateral mosfets with vertical ones, sounded ok to me (Class A, Naturally !)
Temperature with class A amplifiers is much more stable, dissipation actually decreases if a load is driven.

btw: does anyone have some experience with Magnatec double Buz's in a single TO3 ?

djk · 9th February 2005, 10:01 AM

"Is there a generic name or classification of FET's with -ve temp coefficient or does one go through the datasheets of each device...."

In general, lateral mos are good for linear operation, vertical are for switching.

If the DRAIN is hooked to the case, is good for switching.

If the SOURCE is hooked to the case, is good for linear.

8th February 2005, 05:12 PM	#1
djdamix diyAudio Member Join Date: Jun 2004 Location: Lyon	does MOSFET need thermal compensation ? I've read that MOSFET need no thermal compensation since when their temperature rise, the current decrease. Does it means I can do without ??? (I use IRFP240 & 9240) Thanks for any comment. David

8th February 2005, 05:36 PM	#2
wimdehaan diyAudio Member Join Date: Sep 2004 Location: n/a	temp comp MOSFETS MosFets like the IRF 240 and equiv. do need some kind of thermal compensation. Only Power Mosfets Like the BUZ900 / 2Sk1058 / 2SK135 do not need this. These devices do have a negative temperature coeficiente, and this will avoid thermal run-a-way.

8th February 2005, 05:53 PM	#5
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	You mean like a lateral or vertical Mosfet. __________________ Looks like Sponge Bob has killed another thread.

8th February 2005, 06:14 PM	#7
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Indeed. IRF (any type) are vertical devices intended for switching and the -ve tempco only happens at quite high currents. Lateral MOSFETs are specifically for audio -- Hitachi, Exicon and Magnatec are the most prominent -- and these have -ve tempco starting in the milliamps range. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

8th February 2005, 07:39 PM	#9
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	Mr Pass stated in one of his articles that he has a "dumpster" load of them, the main reason for his choice. I think he referred to it as a stategic reserve, good thing he is not in the Silver business. I have the impresion it was Mr Pass who made the vertical IRF's more accepted. The main reason for lateral Hitachi Mosfet in the 80s and 90s was their availability, the ruggid TO3 package, low Ciss, and most of all their 'good' sound. In those days verticals were generally considered a NoNo., even diy mags advised not to go for vertical mosfets. Overhere companies as Silltech pushed the popularity of laterals, in Oz a company as Perreaux, in the US Conrad Johnson and some others. I built a few amps designed for lateral mosfets with vertical ones, sounded ok to me (Class A, Naturally !) Temperature with class A amplifiers is much more stable, dissipation actually decreases if a load is driven. btw: does anyone have some experience with Magnatec double Buz's in a single TO3 ? __________________ Looks like Sponge Bob has killed another thread.


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8th February 2005, 05:41 PM	#3
djdamix diyAudio Member Join Date: Jun 2004 Location: Lyon	thanks for your input, but it's irf"P"240 and IRF"P"9240, I think they are power devices ... David

8th February 2005, 06:11 PM	#6
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Si Senor....

8th February 2005, 06:16 PM	#8
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Thank you Sir! So Slone likes Laterals and Nelson likes vertical FETS... what gives?

9th February 2005, 10:01 AM	#10
djk diyAudio Member Join Date: Feb 2001 Location: USA	"Is there a generic name or classification of FET's with -ve temp coefficient or does one go through the datasheets of each device...." In general, lateral mos are good for linear operation, vertical are for switching. If the DRAIN is hooked to the case, is good for switching. If the SOURCE is hooked to the case, is good for linear.

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