gate resistor of a MOSFET

[kappa_am]

hi,
there is a question. to design proper drive I implement a very simple circuit. I turn on a DC lamp with a MOSFET. why when I reduce gate resistor ( from 120ohm to 18ohm), the mosfet does not get fully saturated and the lamp turn on with reduced light and mosfet gets hot. obviously it work in active region. why? , while with reduced gate resistor it must be get saturated rapidly.
I would be appreciated if you reply to my question.

 

[esp1]

hi,
Is the Gate resistor in series with the Gate input or from Gate to 0V.?
E

 

[FvM]

I guess you managed to build an oscillator. This can happen if the circuit has large source inductance, e.g. on a breadboard. In this case a large gate resistor is helpful to stop oscillations.

 

[kappa_am]

the resistor is series between driver and MOSFET. The driver is implemented on PCB and wired to mosfet; the distance is about 20cm.