Temperature coefficient MOSFET vs. temperature coefficient of BJT












5














If you use transistors for an amplifier scheme, you want to make sure that when you parallel devices, you don't start to conduct more current if your transistors heat up.



I know that when using MOSFETs you always have negative feedback. If one takes more current, it will heat up more, and therefore the resistance will become bigger, and you will conduct less.



When using a BJT the device that dissipates the most current, will heat up most and will start conducting even more. This is unsafe and to solve this I always place a small resistance in series with the emitter.



But what is the physical explanation that in a MOSFET you have this positive temperature coefficient and in a BJT you have this negative coefficient?






mosfet amplifier bjt temperature parallel







share|improve this question
























  • Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
    – analogsystemsrf
    2 days ago
















5














If you use transistors for an amplifier scheme, you want to make sure that when you parallel devices, you don't start to conduct more current if your transistors heat up.



I know that when using MOSFETs you always have negative feedback. If one takes more current, it will heat up more, and therefore the resistance will become bigger, and you will conduct less.



When using a BJT the device that dissipates the most current, will heat up most and will start conducting even more. This is unsafe and to solve this I always place a small resistance in series with the emitter.



But what is the physical explanation that in a MOSFET you have this positive temperature coefficient and in a BJT you have this negative coefficient?






mosfet amplifier bjt temperature parallel







share|improve this question
























  • Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
    – analogsystemsrf
    2 days ago














5












5








5


1





If you use transistors for an amplifier scheme, you want to make sure that when you parallel devices, you don't start to conduct more current if your transistors heat up.



I know that when using MOSFETs you always have negative feedback. If one takes more current, it will heat up more, and therefore the resistance will become bigger, and you will conduct less.



When using a BJT the device that dissipates the most current, will heat up most and will start conducting even more. This is unsafe and to solve this I always place a small resistance in series with the emitter.



But what is the physical explanation that in a MOSFET you have this positive temperature coefficient and in a BJT you have this negative coefficient?






mosfet amplifier bjt temperature parallel







share|improve this question















If you use transistors for an amplifier scheme, you want to make sure that when you parallel devices, you don't start to conduct more current if your transistors heat up.



I know that when using MOSFETs you always have negative feedback. If one takes more current, it will heat up more, and therefore the resistance will become bigger, and you will conduct less.



When using a BJT the device that dissipates the most current, will heat up most and will start conducting even more. This is unsafe and to solve this I always place a small resistance in series with the emitter.



But what is the physical explanation that in a MOSFET you have this positive temperature coefficient and in a BJT you have this negative coefficient?






mosfet amplifier bjt temperature parallel




mosfet amplifier bjt temperature parallel






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 days ago









Peter Mortensen

1,59031422




1,59031422










asked 2 days ago









J. Joly

508




508












  • Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
    – analogsystemsrf
    2 days ago


















  • Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
    – analogsystemsrf
    2 days ago
















Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
– analogsystemsrf
2 days ago




Old style power mosfets were safe; the automotive industry and the satellite industry(JPL) discovered the new-style mosfets are not safe. NASA has some papers out on this.
– analogsystemsrf
2 days ago










1 Answer
1






active

oldest

votes


















6














I do not know the answer to your question about physic behind this.



But your statement about MOSFET temperature coefficient is only true when MOSFET work as a switch.



In linear region (saturation) most MOSFET will have as a negative temperature coefficient as BJT have.



And in general terms, the MOSFET can have negative, positive and zero temperature coefficient.
And we can see this on Transfer characteristic Id=f(Vgs) in the datasheet.



enter image description here



More here



https://www.infineon.com/dgdl/Infineon-ApplicationNote_Linear_Mode_Operation_Safe_Operation_Diagram_MOSFETs-AN-v01_00-EN.pdf?fileId=db3a30433e30e4bf013e3646e9381200



https://www.onsemi.com/pub/Collateral/AND8199-D.PDF



And here I found a specially designed MOSFET for audio amplifiers application.



http://www.exicon.info/PDFs/ecw20n20-z.pdf



enter image description here



As you can see for this lateral MOSFET if you set the quiescent current at Id > 0.2A you are in the safe zone (zero or positive temperature coefficient)
And no temperature compensation network is needed.






share|improve this answer























  • okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
    – J. Joly
    2 days ago










  • Related: electronics.stackexchange.com/a/357641/17387
    – try-catch-finally
    2 days ago






  • 1




    @J.Joly Are you building a class D amplifier?
    – G36
    2 days ago






  • 3




    That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
    – Brian Drummond
    2 days ago






  • 1




    Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
    – G36
    2 days ago











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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









6














I do not know the answer to your question about physic behind this.



But your statement about MOSFET temperature coefficient is only true when MOSFET work as a switch.



In linear region (saturation) most MOSFET will have as a negative temperature coefficient as BJT have.



And in general terms, the MOSFET can have negative, positive and zero temperature coefficient.
And we can see this on Transfer characteristic Id=f(Vgs) in the datasheet.



enter image description here



More here



https://www.infineon.com/dgdl/Infineon-ApplicationNote_Linear_Mode_Operation_Safe_Operation_Diagram_MOSFETs-AN-v01_00-EN.pdf?fileId=db3a30433e30e4bf013e3646e9381200



https://www.onsemi.com/pub/Collateral/AND8199-D.PDF



And here I found a specially designed MOSFET for audio amplifiers application.



http://www.exicon.info/PDFs/ecw20n20-z.pdf



enter image description here



As you can see for this lateral MOSFET if you set the quiescent current at Id > 0.2A you are in the safe zone (zero or positive temperature coefficient)
And no temperature compensation network is needed.






share|improve this answer























  • okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
    – J. Joly
    2 days ago










  • Related: electronics.stackexchange.com/a/357641/17387
    – try-catch-finally
    2 days ago






  • 1




    @J.Joly Are you building a class D amplifier?
    – G36
    2 days ago






  • 3




    That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
    – Brian Drummond
    2 days ago






  • 1




    Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
    – G36
    2 days ago
















6














I do not know the answer to your question about physic behind this.



But your statement about MOSFET temperature coefficient is only true when MOSFET work as a switch.



In linear region (saturation) most MOSFET will have as a negative temperature coefficient as BJT have.



And in general terms, the MOSFET can have negative, positive and zero temperature coefficient.
And we can see this on Transfer characteristic Id=f(Vgs) in the datasheet.



enter image description here



More here



https://www.infineon.com/dgdl/Infineon-ApplicationNote_Linear_Mode_Operation_Safe_Operation_Diagram_MOSFETs-AN-v01_00-EN.pdf?fileId=db3a30433e30e4bf013e3646e9381200



https://www.onsemi.com/pub/Collateral/AND8199-D.PDF



And here I found a specially designed MOSFET for audio amplifiers application.



http://www.exicon.info/PDFs/ecw20n20-z.pdf



enter image description here



As you can see for this lateral MOSFET if you set the quiescent current at Id > 0.2A you are in the safe zone (zero or positive temperature coefficient)
And no temperature compensation network is needed.






share|improve this answer























  • okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
    – J. Joly
    2 days ago










  • Related: electronics.stackexchange.com/a/357641/17387
    – try-catch-finally
    2 days ago






  • 1




    @J.Joly Are you building a class D amplifier?
    – G36
    2 days ago






  • 3




    That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
    – Brian Drummond
    2 days ago






  • 1




    Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
    – G36
    2 days ago














6












6








6






I do not know the answer to your question about physic behind this.



But your statement about MOSFET temperature coefficient is only true when MOSFET work as a switch.



In linear region (saturation) most MOSFET will have as a negative temperature coefficient as BJT have.



And in general terms, the MOSFET can have negative, positive and zero temperature coefficient.
And we can see this on Transfer characteristic Id=f(Vgs) in the datasheet.



enter image description here



More here



https://www.infineon.com/dgdl/Infineon-ApplicationNote_Linear_Mode_Operation_Safe_Operation_Diagram_MOSFETs-AN-v01_00-EN.pdf?fileId=db3a30433e30e4bf013e3646e9381200



https://www.onsemi.com/pub/Collateral/AND8199-D.PDF



And here I found a specially designed MOSFET for audio amplifiers application.



http://www.exicon.info/PDFs/ecw20n20-z.pdf



enter image description here



As you can see for this lateral MOSFET if you set the quiescent current at Id > 0.2A you are in the safe zone (zero or positive temperature coefficient)
And no temperature compensation network is needed.






share|improve this answer














I do not know the answer to your question about physic behind this.



But your statement about MOSFET temperature coefficient is only true when MOSFET work as a switch.



In linear region (saturation) most MOSFET will have as a negative temperature coefficient as BJT have.



And in general terms, the MOSFET can have negative, positive and zero temperature coefficient.
And we can see this on Transfer characteristic Id=f(Vgs) in the datasheet.



enter image description here



More here



https://www.infineon.com/dgdl/Infineon-ApplicationNote_Linear_Mode_Operation_Safe_Operation_Diagram_MOSFETs-AN-v01_00-EN.pdf?fileId=db3a30433e30e4bf013e3646e9381200



https://www.onsemi.com/pub/Collateral/AND8199-D.PDF



And here I found a specially designed MOSFET for audio amplifiers application.



http://www.exicon.info/PDFs/ecw20n20-z.pdf



enter image description here



As you can see for this lateral MOSFET if you set the quiescent current at Id > 0.2A you are in the safe zone (zero or positive temperature coefficient)
And no temperature compensation network is needed.







share|improve this answer














share|improve this answer



share|improve this answer








edited 2 days ago

























answered 2 days ago









G36

5,0601511




5,0601511












  • okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
    – J. Joly
    2 days ago










  • Related: electronics.stackexchange.com/a/357641/17387
    – try-catch-finally
    2 days ago






  • 1




    @J.Joly Are you building a class D amplifier?
    – G36
    2 days ago






  • 3




    That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
    – Brian Drummond
    2 days ago






  • 1




    Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
    – G36
    2 days ago


















  • okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
    – J. Joly
    2 days ago










  • Related: electronics.stackexchange.com/a/357641/17387
    – try-catch-finally
    2 days ago






  • 1




    @J.Joly Are you building a class D amplifier?
    – G36
    2 days ago






  • 3




    That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
    – Brian Drummond
    2 days ago






  • 1




    Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
    – G36
    2 days ago
















okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
– J. Joly
2 days ago




okay good sidenote that I didn't know. Thanks, I'll keep this in mind! I was talking about an amplifier circuit, so as you mentioned I was using the MOSFET as a switch. But still have to keep your comment in mind! Thanks!
– J. Joly
2 days ago












Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
2 days ago




Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
2 days ago




1




1




@J.Joly Are you building a class D amplifier?
– G36
2 days ago




@J.Joly Are you building a class D amplifier?
– G36
2 days ago




3




3




That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 days ago




That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 days ago




1




1




Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
– G36
2 days ago




Also good read about this you can find here sound.whsites.net/articles/hexfet.htm#s51
– G36
2 days ago


















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