Temperature coefficient MOSFET vs. temperature coefficient of BJT
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
edited 1 hour ago
Peter Mortensen
1,58031422
asked 5 hours ago
J. Joly
113
add a comment |
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
edited 1 hour ago
Peter Mortensen
1,58031422
asked 5 hours ago
J. Joly
113
add a comment |
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
edited 1 hour ago
Peter Mortensen
1,58031422
asked 5 hours ago
J. Joly
113
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
edited 1 hour ago
Peter Mortensen
1,58031422
asked 5 hours ago
J. Joly
113
edited 1 hour ago
Peter Mortensen
1,58031422
asked 5 hours ago
J. Joly
113
edited 1 hour ago
Peter Mortensen
1,58031422
edited 1 hour ago
Peter Mortensen
1,58031422
edited 1 hour ago
Peter Mortensen
1,58031422
1,58031422
asked 5 hours ago
J. Joly
113
asked 5 hours ago
J. Joly
113
asked 5 hours ago
J. Joly
113
113
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
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.
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
answered 4 hours ago
G36
4,9051511
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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
|
show 3 more comments
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1 Answer
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oldest
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1 Answer
1
active
oldest
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active
oldest
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active
oldest
votes
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.
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
answered 4 hours ago
G36
4,9051511
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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
|
show 3 more comments
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.
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
answered 4 hours ago
G36
4,9051511
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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
|
show 3 more comments
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.
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
answered 4 hours ago
G36
4,9051511
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.
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
answered 4 hours ago
G36
4,9051511
answered 4 hours ago
G36
4,9051511
answered 4 hours ago
G36
4,9051511
answered 4 hours ago
G36
4,9051511
4,9051511
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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
|
show 3 more comments
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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours 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
4 hours 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
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
Related: electronics.stackexchange.com/a/357641/17387
– try-catch-finally
4 hours ago
1
1
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
@J.Joly Are you building a class D amplifier?
– G36
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
I'm not building it, I'm trying to analyse it. MOSFET power amplifier
– J. Joly
3 hours ago
3
3
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
That schematic shows a linear (not switching) amplifier so you are NOT using the MOSFET as a switch.
– Brian Drummond
2 hours ago
|
show 3 more comments
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