Breaktru Forum
eCigarette Forum => Modding => Topic started by: carlsoti on December 20, 2014, 08:52:34 AM
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I've spent WAY too many hours staring at spec sheets, not fully understanding how all the different parameters affect each other. My mind is squishy from all the graphs.
Can someone be a real champ and point me towards something in the vein of "The be-all, end-all" of SMT Mosfets for for a dual parallel 18650 mod box?
Thanks.
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Well there's no MOSFET that's going to the be the best period. You have to consider voltages since that's going to effect other aspects of the transistor. There's also whether you want or need to switch the high side or low side. That determines the required channel polarity.
There's a ton of specs in the data sheets for MOSFETs, but they are used for other things besides user power switches and that's where all those specs become important. For the application here there's only two specs you need to be concerned with, the on-state resistance and gate-source threshold voltage. Often there's a chart in the data sheet that shows on-state resistance versus gate-source voltage. That chart is the only thing you need to look at. Not all MOSFET data-sheets have that chart, but all the later model parts do and the newer parts are the best ones.
Otherwise without looking at that graph, on-state resistances are typically listed at the top of the data sheet for various gate-source voltages. If the only ones listed are at 4.5V and 10V, gate-source threshold voltage may be too high for use with a single cell or parallel cells. The graph tells you one way or the other for sure.
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I have been looking at surface mount n-channel mosfets recently myself. Here are a few I had bookmarked:
• http://www.mouser.com/ProductDetail/International-Rectifier/IRLS3034TRLPBF/?qs=sGAEpiMZZMshyDBzk1%2fWi5%252bqVgN3%252bWS8ugGwhNF3grg%3d
• http://www.mouser.com/ProductDetail/NXP-Semiconductors/PSMN1R1-25YLC115/?qs=sGAEpiMZZMshyDBzk1%2fWi%252bFHavO7hMd5ZCHgcLfhazw%3d
• http://www.mouser.com/ProductDetail/NXP-Semiconductors/PSMN1R0-30YLC115/?qs=sGAEpiMZZMshyDBzk1%2fWi%252bvkfjHXHLK4iGM2XeQ0%2fEE%3d
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Thanks guys. My brain is a bit more recharged at this point. I guess the frustrating part is that not all the specs published are the same amongst different manufacturers.
CraigHB, you posted the the link to a Vishay part# SiR404DP in another thread. This one actually has the RDS(on)-VGS graph. In comparison to the specs for the IRLB3813PBF I have, as pointed out by, David4500, it appears to be light-years better for my application.