On Sun, Oct 18, 2009 at 8:27 AM, Kevin wrote: > What's the difference between Vgs and Vgs(th) I thought the > Vgs(th) was the voltage to turn it on fully ? > Vgs(th) is the voltage where a pre-defined level of current can flow. To turn it on fully you need a higher voltage. Check the Ids vs. Vgs graphs in the datasheet. You want the voltage to be well above whatever your maximum current will be. Most of the time this ends up being 12v or sometimes 15v (for normal MOSFETs) Logic-level MOSFETs have a lower Vth so you can get by with a lower gate voltage, but the Rd-s resistance is higher. -- Martin K. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist