i did some tests with fdp8440 power mosfet and mic4452 9a mosfet driver ic .
the load was simple dc motor (with protection diode), frequency is 30khz .
i noticed that mosfet loses significantly dropped with lower gate resistors ,and the lowest loses were when i used no gate resistor at all .
the question is , can the power mosfet be damaged due to too high dv/dt at the gate ?
and what other negative effects should be considered when driving the mosfets with no gate resistor ?
the load was simple dc motor (with protection diode), frequency is 30khz .
i noticed that mosfet loses significantly dropped with lower gate resistors ,and the lowest loses were when i used no gate resistor at all .
the question is , can the power mosfet be damaged due to too high dv/dt at the gate ?
and what other negative effects should be considered when driving the mosfets with no gate resistor ?
The answer is yes.
http://www.irf.com/technical-info/appnotes/mosfet.pdf
See page 11 dv/dt CAPABILITY
http://www.irf.com/technical-info/appnotes/mosfet.pdf
See page 11 dv/dt CAPABILITY
if you read this page , its about high dv/dt at the drain-source that could rapidly turn on the mosfet . they even advise to use lower gate resistance to solve this problem .
so its not exactly answering my question 🙂
Hi,
not damage. is not possible increments dv / dt in addition to physical MOSFET. only in linear driving (eg. class AB amp), rg limits the possibility of oscillations and IG.
when using as a switch and do not need the high impedance, it can linearize the curve by placing a charge in parallel res (gate.drain) of very low value.
not damage. is not possible increments dv / dt in addition to physical MOSFET. only in linear driving (eg. class AB amp), rg limits the possibility of oscillations and IG.
when using as a switch and do not need the high impedance, it can linearize the curve by placing a charge in parallel res (gate.drain) of very low value.
gate resistor is
1. for damping the switching transition to aid EMC
2. Damping resonances between gate cct stray L and Drain-gate capacitance.
3. Reducing gate drive level to level acceptable to driver.
1. for damping the switching transition to aid EMC
2. Damping resonances between gate cct stray L and Drain-gate capacitance.
3. Reducing gate drive level to level acceptable to driver.
second that
check the voltage spikes at the drain of the MOSFET, when it is switching very fast (== low gate resistance) the voltage spike will be higher and higher, eventually exceeding the breakdown voltage of the MOSFET. safety margin of 20% is very appropriate here.
and, with low or no gate resistor, chances are parasitic oscillations may develop. the compromise that is usually done is to increase the gate resistor just so much that you dont see parasitic oscillations, voltage spikes are controlled, EMI is within the limits. The power losses will go up a little bit but not much, usually.
just my two cents
check the voltage spikes at the drain of the MOSFET, when it is switching very fast (== low gate resistance) the voltage spike will be higher and higher, eventually exceeding the breakdown voltage of the MOSFET. safety margin of 20% is very appropriate here.
and, with low or no gate resistor, chances are parasitic oscillations may develop. the compromise that is usually done is to increase the gate resistor just so much that you dont see parasitic oscillations, voltage spikes are controlled, EMI is within the limits. The power losses will go up a little bit but not much, usually.
just my two cents
Hi,
Just for clarify.
r series, all use even a minimum value in the gate eg.1R (including me).
I answered the question. (fails to increase the mosfet dt / dv).
can not be increased.
and, it is good to adapt the voltage of the driver (not with R gate).
is good, get a clean square wave, instead of increasing the R-gate.
Regards
Just for clarify.
r series, all use even a minimum value in the gate eg.1R (including me).
I answered the question. (fails to increase the mosfet dt / dv).
can not be increased.
and, it is good to adapt the voltage of the driver (not with R gate).
is good, get a clean square wave, instead of increasing the R-gate.
Regards
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