Why does turning a MOSFET ON too fast cause ringing?
Going though app notes, I can understand that turning it off (i.e. when drain-source voltage is increasing) can cause ringing due to parasitic NPN and also drain-gate capacitor which can charge the gate and turn the MOSFET back on, if the dv/dt is high enough.
But what's the reason behind ringing when turning the MOSFET ON? (i.e. when drain-source voltage is decreasing) How exactly does it happen?
Update:
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (As turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET.)
mosfet driver ringing
add a comment |
Going though app notes, I can understand that turning it off (i.e. when drain-source voltage is increasing) can cause ringing due to parasitic NPN and also drain-gate capacitor which can charge the gate and turn the MOSFET back on, if the dv/dt is high enough.
But what's the reason behind ringing when turning the MOSFET ON? (i.e. when drain-source voltage is decreasing) How exactly does it happen?
Update:
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (As turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET.)
mosfet driver ringing
reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
2
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago
add a comment |
Going though app notes, I can understand that turning it off (i.e. when drain-source voltage is increasing) can cause ringing due to parasitic NPN and also drain-gate capacitor which can charge the gate and turn the MOSFET back on, if the dv/dt is high enough.
But what's the reason behind ringing when turning the MOSFET ON? (i.e. when drain-source voltage is decreasing) How exactly does it happen?
Update:
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (As turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET.)
mosfet driver ringing
Going though app notes, I can understand that turning it off (i.e. when drain-source voltage is increasing) can cause ringing due to parasitic NPN and also drain-gate capacitor which can charge the gate and turn the MOSFET back on, if the dv/dt is high enough.
But what's the reason behind ringing when turning the MOSFET ON? (i.e. when drain-source voltage is decreasing) How exactly does it happen?
Update:
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (As turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET.)
mosfet driver ringing
mosfet driver ringing
edited 3 hours ago
JRE
20.7k43768
20.7k43768
asked 6 hours ago
Sudoer
15610
15610
reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
2
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago
add a comment |
reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
2
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago
reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
2
2
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago
add a comment |
1 Answer
1
active
oldest
votes
Schematic from original question:
Presumably this will be connected to a load, so current will travel in this loop:
GND - Power supply decoupling caps - Load - FET - GND
This loop has inductance due to trace/wire length, and maybe the load has some inductance too. Thus it will form a LC resonant circuit with the FET's parasitic drain-source cap when the FET is OFF, and with the supply decoupling caps when the FET is ON. Both are may ring, at their own resonant frequencies which will most likely not be the same.
Ringing when the FET turns OFF is easy to observe on the drain voltage. Since the capacitance is small, it will usually ring at a high frequency also.
Ringing when it turns ON is not easy to observe as there will be very little voltage swing. That doesn't mean you won't get a ringing current inside the traces/wires, which can couple into other circuits, radiate, or cause unwanted voltage drops on GND. Whether it rings or not depends on damping, if there is enough ESR in the caps, the FET and the load, etc. I think ringing on turn-on should be pretty rare, since it involves the supply caps it would require lots of inductance in the load.
Also, a very important factor is that if the load is connected via wires, you really don't want to have high di/dt in them whether at turn-on or turn-off, as that would make a nice wideband radio jammer. These FET drivers are capable of very fast switching, which is a EMI headache, and slowing the switching to "as fast as you need but not faster" helps.
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
add a comment |
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Schematic from original question:
Presumably this will be connected to a load, so current will travel in this loop:
GND - Power supply decoupling caps - Load - FET - GND
This loop has inductance due to trace/wire length, and maybe the load has some inductance too. Thus it will form a LC resonant circuit with the FET's parasitic drain-source cap when the FET is OFF, and with the supply decoupling caps when the FET is ON. Both are may ring, at their own resonant frequencies which will most likely not be the same.
Ringing when the FET turns OFF is easy to observe on the drain voltage. Since the capacitance is small, it will usually ring at a high frequency also.
Ringing when it turns ON is not easy to observe as there will be very little voltage swing. That doesn't mean you won't get a ringing current inside the traces/wires, which can couple into other circuits, radiate, or cause unwanted voltage drops on GND. Whether it rings or not depends on damping, if there is enough ESR in the caps, the FET and the load, etc. I think ringing on turn-on should be pretty rare, since it involves the supply caps it would require lots of inductance in the load.
Also, a very important factor is that if the load is connected via wires, you really don't want to have high di/dt in them whether at turn-on or turn-off, as that would make a nice wideband radio jammer. These FET drivers are capable of very fast switching, which is a EMI headache, and slowing the switching to "as fast as you need but not faster" helps.
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
add a comment |
Schematic from original question:
Presumably this will be connected to a load, so current will travel in this loop:
GND - Power supply decoupling caps - Load - FET - GND
This loop has inductance due to trace/wire length, and maybe the load has some inductance too. Thus it will form a LC resonant circuit with the FET's parasitic drain-source cap when the FET is OFF, and with the supply decoupling caps when the FET is ON. Both are may ring, at their own resonant frequencies which will most likely not be the same.
Ringing when the FET turns OFF is easy to observe on the drain voltage. Since the capacitance is small, it will usually ring at a high frequency also.
Ringing when it turns ON is not easy to observe as there will be very little voltage swing. That doesn't mean you won't get a ringing current inside the traces/wires, which can couple into other circuits, radiate, or cause unwanted voltage drops on GND. Whether it rings or not depends on damping, if there is enough ESR in the caps, the FET and the load, etc. I think ringing on turn-on should be pretty rare, since it involves the supply caps it would require lots of inductance in the load.
Also, a very important factor is that if the load is connected via wires, you really don't want to have high di/dt in them whether at turn-on or turn-off, as that would make a nice wideband radio jammer. These FET drivers are capable of very fast switching, which is a EMI headache, and slowing the switching to "as fast as you need but not faster" helps.
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
add a comment |
Schematic from original question:
Presumably this will be connected to a load, so current will travel in this loop:
GND - Power supply decoupling caps - Load - FET - GND
This loop has inductance due to trace/wire length, and maybe the load has some inductance too. Thus it will form a LC resonant circuit with the FET's parasitic drain-source cap when the FET is OFF, and with the supply decoupling caps when the FET is ON. Both are may ring, at their own resonant frequencies which will most likely not be the same.
Ringing when the FET turns OFF is easy to observe on the drain voltage. Since the capacitance is small, it will usually ring at a high frequency also.
Ringing when it turns ON is not easy to observe as there will be very little voltage swing. That doesn't mean you won't get a ringing current inside the traces/wires, which can couple into other circuits, radiate, or cause unwanted voltage drops on GND. Whether it rings or not depends on damping, if there is enough ESR in the caps, the FET and the load, etc. I think ringing on turn-on should be pretty rare, since it involves the supply caps it would require lots of inductance in the load.
Also, a very important factor is that if the load is connected via wires, you really don't want to have high di/dt in them whether at turn-on or turn-off, as that would make a nice wideband radio jammer. These FET drivers are capable of very fast switching, which is a EMI headache, and slowing the switching to "as fast as you need but not faster" helps.
Schematic from original question:
Presumably this will be connected to a load, so current will travel in this loop:
GND - Power supply decoupling caps - Load - FET - GND
This loop has inductance due to trace/wire length, and maybe the load has some inductance too. Thus it will form a LC resonant circuit with the FET's parasitic drain-source cap when the FET is OFF, and with the supply decoupling caps when the FET is ON. Both are may ring, at their own resonant frequencies which will most likely not be the same.
Ringing when the FET turns OFF is easy to observe on the drain voltage. Since the capacitance is small, it will usually ring at a high frequency also.
Ringing when it turns ON is not easy to observe as there will be very little voltage swing. That doesn't mean you won't get a ringing current inside the traces/wires, which can couple into other circuits, radiate, or cause unwanted voltage drops on GND. Whether it rings or not depends on damping, if there is enough ESR in the caps, the FET and the load, etc. I think ringing on turn-on should be pretty rare, since it involves the supply caps it would require lots of inductance in the load.
Also, a very important factor is that if the load is connected via wires, you really don't want to have high di/dt in them whether at turn-on or turn-off, as that would make a nice wideband radio jammer. These FET drivers are capable of very fast switching, which is a EMI headache, and slowing the switching to "as fast as you need but not faster" helps.
edited 4 hours ago
answered 5 hours ago
peufeu
24.8k23972
24.8k23972
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
add a comment |
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
I found this app note: "Parasitic Oscillation and Ringing of Power MOSFETs - TOSHIBA Semiconductor" but it only discusses ringing when switching the MOSFET off ... do you of any paper that discusses ringing when you switch the MOSFET on? Thanks
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Also: isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
Could it be that when people refer to ringing when turning on the MOSFET, they refer specifically to half/full bridge, and not a circuit with only a low side MOSFET? (as turning on the high side MOSFET would cause a positive dv/dt on the low side MOSFET)
– Sudoer
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
"isn't the loop open when the switch is off" -> if there was current in the loop and the FET turns off, the energy stored in the magnetic field has to go somewhere. Can be a flywheel diode, FET avalanche, or ringing.
– peufeu
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
but my question is about when the switch is currently/previously off and we want to turn it on. when the switch is off there is no current in the loop thus no energy ... isn't that the case?
– Sudoer
4 hours ago
add a comment |
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reference to the original question: electronics.stackexchange.com/questions/414759/…
– Sudoer
6 hours ago
2
Parasitic inductances and capacitances in the loop for one thing.
– Unimportant
5 hours ago
@Unimportant isn't the loop open when the switch is off? there should be no energy in drain parasitic inductance etc when the switch is off and no current is flowing ... so where does the ringing voltage come from during falling edge of the Vds? (i.e. when the switch is turning on) (if it does as pointed out in the original question)
– Sudoer
4 hours ago
Ringing can mean one thing to one guy and another thing to another guy. Do you have a waveform shot so it rules out speculation?
– Andy aka
3 hours ago