Drain source voltage slope of MOSFET??

[forever074]

1. I often see parameter "Drain source voltage slope" in datasheet of MOSFET.
EG: in datasheet of mosfet SPW35N60CFD, Drain source voltage slope dv/dt=80V/ns

So what does Drain source voltage slope mean? Is that the maximum dv/dt rating?
2. When we select R_gate to driver MOSFET, what is minimum of R_gate?
How R_gate related to Drain source voltage slope?

 

[Harald Kapp]

Is that the maximum dv/dt rating?

Yes ist is. If the voltage rises faster, the transistor may turn on due to curent flowing into the drain-gate capacitace. Turning on the transistor when it is supposed to be off can damage the transistor and the circuit.

The minimum Rgate = 0 Ohm. What value is suitable for the circuit depends on the circuit and its parameters.
Obviously, if Rgate is large, the charge current through Cdg due to dVds/dt will chareg the gate more easily and therefore turn on the transistor at lower dV/dt. If Rgate is small, it will drain part of the charge current through Cdg and the transistor is kept of at higher dV/dt (but not higher than the max. value stated in the datasheet).

Here are some MOSFET parameters explained.

 

[forever074]

@Harald Kapp . When we driver MOSFET with a Rgate at high frequency( Eg 100kHz), In my opinion I think The less Rgate is the less switching loss is. So why we dont select Rgate=0OHM. What does we select Rgate depending on?

 

[Harald Kapp]

The gate source capacitance is comparatively large. If you switch the gate voltage without series resistor, high current spikes are the consequence which is bad for electromagnetic compatibility (EMC) because it generates a lot of "noise".

Here is some stuff to read up:
http://www.fairchildsemi.com/an/AN/AN-9068.pdf
http://www.vishay.com/docs/73217/73217.pdf