Fet Drive Circuit With Pic Micro

[ClydeCrashKop]

Can’t you just use a logic level FET like IRL520N or IRL3103 on the low side and treat it like a gate?

 

[cadstarsucks]

Can’t you just use a logic level FET like IRL520N or IRL3103 on the low side and treat it like a gate?

You can but trying to PWM a FET with only 20mA of gate drive would burn it up.

D.

 

[dknguyen]

Current is also needed in order to charge up the gate-source capacitance in a FET in addition to the gate voltage. So although you can switch the IR520N on with a logic level, you cannot switch it very fast since it's GS capacitance is too high for the current that can be sourced by a PIC. It needs to be a small, logic level FET with low gate capacitance.

 

[cadstarsucks]

Current is also needed in order to charge up the gate-source capacitance in a FET in addition to the gate voltage. So although you can switch the IR520N on with a logic level, you cannot switch it very fast since it's GS capacitance is too high for the current that can be sourced by a PIC. It needs to be a small, logic level FET with low gate capacitance.

I'm not sure who you are responding to here. I have been saying that...Mind you, there are no FETs such as what you describe that will switch the currents that the ones that were listed earlier can.

D.

 

[gramo]

Thanks for all your help with this, just one more thing to query before I implement it,

Are 2N3904 and 2N3905 transistors suffice for the switching currents involved?


Both can handle 200mA, thats 100mA more than the BC550 and BC558 in the diagram I supplied on my original post

 

[cadstarsucks]

Thanks for all your help with this, just one more thing to query before I implement it,

Are 2N3904 and 2N3905 transistors suffice for the switching currents involved?


Both can handle 200mA, thats 100mA more than the BC550 and BC558 in the diagram I supplied on my original post

It is very much a case of the more the merrier, however for what you are doing they will probably be fine.

Dan