MOSFET datasheet question

D Faust

Where on a data sheet can I find the fully on voltage of a MOSFET?(or what is it labeled as?)· It isn't V(GS) is it? Thanks.

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D Faust

Phil Pilgrim (PhiPi)

Many datasheets list values of R_DS(on) for various values of V_GS. This will give you an idea of what constitutes "fully on" for your application. In some cases you may have to look at a graph of R_DS(on) versus V_GS to come to a conclusion.

In either case, you then have to make sure that your anticipated I_DS² R_DS(on) doesn't exceed the power dissipation limits of the device, along with any heatsinking you may have added.

-Phil

D Faust

Thank you, I understand what you are saying, but I have yet to find such a table or graph.·· I am looking at this datasheet: (http://www.ortodoxism.ro/datasheets/fairchild/IRF510.pdf)

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D Faust

stamptrol

D Faust,

On the first page under "Features", Rds(on) is shown as 0.54 ohms.

Then refer to Figure 5 and 6, which shows the performance at various gate-to-source voltages.

This is a good general purpose FET because it operates at low gate voltages.

Cheers,

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Tom Sisk

http://www.siskconsult.com
·

D Faust

O.K., I am not so sure about this, so it would be greatly appreciated if someone could correct me. If V(GS) is 5V and V(DS) is 6V, then the transistor allows one amp through.(based on figure 6) Also if V(GS) is 4V then there is no amperage at the drain.

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D Faust

Phil Pilgrim (PhiPi)

Yes and no. You need to consider the test conditions given in these figures, namely that they're for a pulse duration of 80uS at a duty cycle of 0.5% or less. With this transistor, the continuous drain current should probably be limited to much less than 1 amp at V_GS = 5V. This is not a "logic" MOSFET, and the R_DS(on) of 0.54 ohms is spec'd at V_GS = 10V. It will likely be much higher than than at V_GS = 5V. A much better choice for driving from a micro would be the IRLZ34N.

You probably got one of the IRF510s at Radio Shack ... right? It's too bad they even offer it instead of a logic MOSFET. I'm sure there are many people who expect these things to sink a lot of current with a logic-level drive and end up being disappointed.

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 7/10/2007 9:14:38 PM GMT

D Faust

Actually Phil, I was looking on Radioshack's website to see what MOSFETs I could get from them.· I heard that other people hand problems with non-logic-level MOSFETs so I wanted to·check the datasheet.· It seems that most logic level MOSFETs have an "L" somewhere·in their part number· Thanks for pointing out·the pulse·comment.· I saw it, but wasn't sure if it meant anything.· Thank you both,·I think·I got it now.

EDIT
[noparse][[/noparse]P.S. Thank you for the link, where is a good place to buy components such as·MOSFETs anyway]

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D Faust

Post Edited (D Faust) : 7/11/2007 1:11:16 AM GMT

Phil Pilgrim (PhiPi)

DigiKey and Mouser both have ample selections of MOSFETs. If your order total is under $25, Mouser is the better source, since they don't charge a $5 service fee for small orders. [Edit: Digikey no longer charges a service fee for small orders.]

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 7/11/2007 1:40:20 AM GMT

D Faust

I had heard of Mouser, but not Digikey. I'll have to check them both before I order. Thanks for the info!

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D Faust

Whit

Phil Pilgrim (PhiPi) said...
DigiKey and Mouser both have ample selections of MOSFETs. If your order total is under $25, Mouser is the better source, since they don't charge a $5 service fee for small orders.

-Phil

Thanks for the small order info Phil!

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Whit+


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