MOSFET ?

[cheap&simple]

how do you size a resistor for the gate of a mosfet
examble 14N05L powered by a 5v. pic chip what size risistor is need
If I am correct the size of the resistor can change how much current the mosfet can carry. but with any gate voltage, mosfet & load how is this figured. just trying to learn
thanks

 

[Optikon]

how do you size a resistor for the gate of a mosfet
examble 14N05L powered by a 5v. pic chip what size risistor is need
If I am correct the size of the resistor can change how much current the mosfet can carry. but with any gate voltage, mosfet & load how is this figured. just trying to learn
thanks

Mosfet Gate currents are VERY small. The resistor in the gate is not used for current limiting in the DC sense. It will limit in the AC peak sense and also forms a low pass filter with the gate parasitic capacitance to effectively slow down the turn on (desirable sometimes)

You may be thinking of a Bipolar transistor. Here the resistor limits the current flowing into the base. Depending on the application, you will need to allow enough base current to support the collector load at minimum forward current gain. Is this the calculation you are after? If you provide an application circuit, it would be much easier to discuss how & why its value is chosen.

 

[Roff]

The gate resistor is also used to damp oscillations or ringing that might otherwise occur.

 

[i_build_stuff]

The gate resistor is sometimes used to slow the MOSFET down in hard-switching circuits (to limit the dV/dt at turn-off and sometimes reduce ringing).

Other than that, I can't see much reason to even have one.

 

[cheap&simple]

so in just general use as a switching device there is no need to add one
as in this app. (14N05L powered by a 5v. pic chip) out put pin to gate and let it go?

 

[Styx]

The gate resistor is also used to damp oscillations or ringing that might otherwise occur.

Ahh yes the dredded unintentional pierce oscillator

 

[Roff]

The gate resistor is also used to damp oscillations or ringing that might otherwise occur.

Ahh yes the dredded unintentional pierce oscillator

I believe a corollary to Murphy's law is "Amplifiers oscillate. Oscillators don't". :lol: