Is turning off MOSFET too fast, bad?
As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through:
a) biasing Parasitic NPN and:
b) charging the GS capacitor through DG capacitor, and thus turning on the MOSFET.
1- is my understanding correct?
2- if yes, then it won't be an issue in the circuit below, which uses a diode to turn off the MOSFET as fast as possible?
3- is that diode even necessary, considering there is only one low side MOSFET, thus no chance of shoot-through?
mosfet driver
asked 4 hours ago
Sudoer
1278
add a comment |
As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through:
a) biasing Parasitic NPN and:
b) charging the GS capacitor through DG capacitor, and thus turning on the MOSFET.
1- is my understanding correct?
2- if yes, then it won't be an issue in the circuit below, which uses a diode to turn off the MOSFET as fast as possible?
3- is that diode even necessary, considering there is only one low side MOSFET, thus no chance of shoot-through?
mosfet driver
asked 4 hours ago
Sudoer
1278
add a comment |
As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through:
a) biasing Parasitic NPN and:
b) charging the GS capacitor through DG capacitor, and thus turning on the MOSFET.
1- is my understanding correct?
2- if yes, then it won't be an issue in the circuit below, which uses a diode to turn off the MOSFET as fast as possible?
3- is that diode even necessary, considering there is only one low side MOSFET, thus no chance of shoot-through?
mosfet driver
asked 4 hours ago
Sudoer
1278
As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through:
a) biasing Parasitic NPN and:
b) charging the GS capacitor through DG capacitor, and thus turning on the MOSFET.
1- is my understanding correct?
2- if yes, then it won't be an issue in the circuit below, which uses a diode to turn off the MOSFET as fast as possible?
3- is that diode even necessary, considering there is only one low side MOSFET, thus no chance of shoot-through?
mosfet driver
mosfet driver
asked 4 hours ago
Sudoer
1278
asked 4 hours ago
Sudoer
1278
asked 4 hours ago
Sudoer
1278
asked 4 hours ago
Sudoer
1278
asked 4 hours ago
Sudoer
1278
1278
add a comment |
add a comment |
1 Answer
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Your understanding is correct. To break down the issues a bit more:
Turning the MOSFET ON too fast can cause overshoot and ringing at the drain, hence the use of a low ohms resistor right at the gate. The ultra fast diode is to turn the MOSFET OFF faster than it turns ON, but the diode has internal resistance. What is bad is driving the gate with no resistor at all.
Yes the diode can be removed for the reasons you mentioned-there is no 'competing' MOSFET. If this were a totem pole or push-pull design the diodes would help insure one is turning OFF before the other MOSFET turns on. This would include both sides of an H-Bridge topology.
At high clock rates and wide pulse widths there is a risk of shoot-through for a totem pole design, or in a push-pull design the core can saturate and blow a fuse, or in a worst case scenario the ferrite core can crack.
answered 3 hours ago
Sparky256
11k21534
add a comment |
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Your understanding is correct. To break down the issues a bit more:
Turning the MOSFET ON too fast can cause overshoot and ringing at the drain, hence the use of a low ohms resistor right at the gate. The ultra fast diode is to turn the MOSFET OFF faster than it turns ON, but the diode has internal resistance. What is bad is driving the gate with no resistor at all.
Yes the diode can be removed for the reasons you mentioned-there is no 'competing' MOSFET. If this were a totem pole or push-pull design the diodes would help insure one is turning OFF before the other MOSFET turns on. This would include both sides of an H-Bridge topology.
At high clock rates and wide pulse widths there is a risk of shoot-through for a totem pole design, or in a push-pull design the core can saturate and blow a fuse, or in a worst case scenario the ferrite core can crack.
answered 3 hours ago
Sparky256
11k21534
add a comment |
Your understanding is correct. To break down the issues a bit more:
Turning the MOSFET ON too fast can cause overshoot and ringing at the drain, hence the use of a low ohms resistor right at the gate. The ultra fast diode is to turn the MOSFET OFF faster than it turns ON, but the diode has internal resistance. What is bad is driving the gate with no resistor at all.
Yes the diode can be removed for the reasons you mentioned-there is no 'competing' MOSFET. If this were a totem pole or push-pull design the diodes would help insure one is turning OFF before the other MOSFET turns on. This would include both sides of an H-Bridge topology.
At high clock rates and wide pulse widths there is a risk of shoot-through for a totem pole design, or in a push-pull design the core can saturate and blow a fuse, or in a worst case scenario the ferrite core can crack.
answered 3 hours ago
Sparky256
11k21534
add a comment |
Your understanding is correct. To break down the issues a bit more:
Turning the MOSFET ON too fast can cause overshoot and ringing at the drain, hence the use of a low ohms resistor right at the gate. The ultra fast diode is to turn the MOSFET OFF faster than it turns ON, but the diode has internal resistance. What is bad is driving the gate with no resistor at all.
Yes the diode can be removed for the reasons you mentioned-there is no 'competing' MOSFET. If this were a totem pole or push-pull design the diodes would help insure one is turning OFF before the other MOSFET turns on. This would include both sides of an H-Bridge topology.
At high clock rates and wide pulse widths there is a risk of shoot-through for a totem pole design, or in a push-pull design the core can saturate and blow a fuse, or in a worst case scenario the ferrite core can crack.
answered 3 hours ago
Sparky256
11k21534
Your understanding is correct. To break down the issues a bit more:
Turning the MOSFET ON too fast can cause overshoot and ringing at the drain, hence the use of a low ohms resistor right at the gate. The ultra fast diode is to turn the MOSFET OFF faster than it turns ON, but the diode has internal resistance. What is bad is driving the gate with no resistor at all.
Yes the diode can be removed for the reasons you mentioned-there is no 'competing' MOSFET. If this were a totem pole or push-pull design the diodes would help insure one is turning OFF before the other MOSFET turns on. This would include both sides of an H-Bridge topology.
At high clock rates and wide pulse widths there is a risk of shoot-through for a totem pole design, or in a push-pull design the core can saturate and blow a fuse, or in a worst case scenario the ferrite core can crack.
answered 3 hours ago
Sparky256
11k21534
edited 44 mins ago
answered 3 hours ago
Sparky256
11k21534
answered 3 hours ago
Sparky256
11k21534
answered 3 hours ago
Sparky256
11k21534
11k21534
add a comment |
add a comment |
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