Signal Fet dissipation

GregH2 · 8th August 2011, 12:21 AM

Hi All,

I have a dissipation question I'm hoping you can help with. I know you Pass guys like pushing your fets so I thought I would ask this here.

I am currently building a mosfet amplifier which has a VAS using ZVP3310A (650mW) and DN2530 (750mW) fets. They are both TO92 devices.

I am interested to know how much dissipation I can comfortably push out of these while still maintaining a long lifespan. The thing I understand about the TO92 package is that it can't dissipate heat very well at high ambient temperatures and needs very severe derating. Let's assume an ambient temperature of 45 degrees C inside the enclosure.

I currently have about 25v across each and am running them at 6mA, but I would like to use a higher current if possible.

Any insight into this would be most appreciated!

Cheers,

Greg.

h_a · 8th August 2011, 05:57 AM

The general rule of thumb is not to exceed half of the power rating, for jfets I would even go lower than that for best reliability.

If you need more current, parallel 'em!

Hannes

GregH2 · 8th August 2011, 06:05 AM

Thanks h_a,

Would you really go that high with an ambient temperature of 45 deg C?

This is great news!

Nelson Pass · 8th August 2011, 07:07 PM

If the max chip temperature is 150, then you can figure that you don't
want to run it past 100 ever, and with a 50 deg ambient and a 5 mw
derating per degree, we get about 250 mW rating figure that I would
consider the maximum just sitting inside an amplifier.

woody · 8th August 2011, 08:58 PM

Nelson, Does this also apply to the Simisouth jfets ? I see on the data sheet they are rated at 150c max. but didn't you mention the chips fail at about 800c ?

Nelson Pass · 8th August 2011, 09:09 PM

I think it is the packaging and die bonding which fails above 175 deg or so.

I feel free to run them up to 100 deg case temperature, no higher.

GregH2 · 8th August 2011, 11:44 PM

Thanks Nelson, this is the kind of info I wanted.

Greg.

woody · 9th August 2011, 06:40 AM

Thanks Nelson I was a little concerned about that heet issue.

8th August 2011, 12:21 AM	#1
GregH2 diyAudio Member Join Date: Oct 2009	Signal Fet dissipation Hi All, I have a dissipation question I'm hoping you can help with. I know you Pass guys like pushing your fets so I thought I would ask this here. I am currently building a mosfet amplifier which has a VAS using ZVP3310A (650mW) and DN2530 (750mW) fets. They are both TO92 devices. I am interested to know how much dissipation I can comfortably push out of these while still maintaining a long lifespan. The thing I understand about the TO92 package is that it can't dissipate heat very well at high ambient temperatures and needs very severe derating. Let's assume an ambient temperature of 45 degrees C inside the enclosure. I currently have about 25v across each and am running them at 6mA, but I would like to use a higher current if possible. Any insight into this would be most appreciated! Cheers, Greg.

8th August 2011, 05:57 AM	#2
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	The general rule of thumb is not to exceed half of the power rating, for jfets I would even go lower than that for best reliability. If you need more current, parallel 'em! Hannes __________________ fresh matched IRFP240/IRFP9240 fets \|\| AlephJ/JX-kits F5 transistor kits \|\| Burning Amp BA-1/2/3 transistor kits

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8th August 2011, 06:05 AM	#3
GregH2 diyAudio Member Join Date: Oct 2009	Thanks h_a, Would you really go that high with an ambient temperature of 45 deg C? This is great news!

8th August 2011, 07:07 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	If the max chip temperature is 150, then you can figure that you don't want to run it past 100 ever, and with a 50 deg ambient and a 5 mw derating per degree, we get about 250 mW rating figure that I would consider the maximum just sitting inside an amplifier.

8th August 2011, 08:58 PM	#5
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	Nelson, Does this also apply to the Simisouth jfets ? I see on the data sheet they are rated at 150c max. but didn't you mention the chips fail at about 800c ?

8th August 2011, 09:09 PM	#6
Nelson Pass The one and only Join Date: Mar 2001	I think it is the packaging and die bonding which fails above 175 deg or so. I feel free to run them up to 100 deg case temperature, no higher.

8th August 2011, 11:44 PM	#7
GregH2 diyAudio Member Join Date: Oct 2009	Thanks Nelson, this is the kind of info I wanted. Greg.

9th August 2011, 06:40 AM	#8
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	Thanks Nelson I was a little concerned about that heet issue.

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