[SOLVED] Differences between logic mosfets and regular mosfets. Help.

[sotron]

Hi.
After searching a lot in the net, maybe not so well. I wanted to control a motor or heavy load directly from a pic microcontroller. People suggested a logic level mosfet which can be driven right out of the micro this is ok, others told me to look for Vgs Gate- source Voltage, but a lot of them are ± 16v or ± 20v and cannot show me which is logic and which is regular. Other say we have to look, for the VGS(th) Gate Threshold Voltage, but this is same in logic and regular mosfets, so no luck here also. A lot of confusing out there, for not experienced mosfet users. So is there some expert in mosfet design and make these figures clear, also if he can tell us what to look in a mosfet for controlling it directly from a microcontroller.

Thanks.
Sotiris

 

[btbass]

Re: Differences between logic mosfets and regular mosfets. H

Logic level mosfets are designed to be driven from Cmos logic drivers, which dont have much power output or voltage swing, so the gate insulation thickness of the mosfet is reduced, which results in a lower gate threshold voltage required, typically ~2 Volts.
If you are using something like a Pic micro, the outputs can source or sink ~20mA and swing to rail. If you have a 5 volt supply, you will be able to drive the average mosfet which typically has a threshold voltage of 2 - 4 volts.

I think the +/-16 volts and +/- 20 volts you are talking about are the breakdown voltages of the gate junction and not the threshold voltages.