# Help picking a specific MOSFET

Hello.

I am currently working on a project that involves a MOSFET, and my teacher has sent me these specs that the MOSFET should have, but I am not sure which specific MOSFET gives these specs.

I will appreciate all the help I can get.

Thank you.

Here's OP's pic.

(OP, for future reference, read this.)

go to one of the parts houses' (Jameco, NTE, Newark, ONsemi,TI,,,) web sites and select MOSFETs. they usually have a search engine where you put in the specs you require

ProjectBegins: I am currently working on a project that involves a MOSFET, and my teacher has sent me these specs that the MOSFET should have, but I am not sure which specific MOSFET gives these specs.

Wouldn't it be easier just to ask your teacher?

Steve

slipstick: Wouldn't it be easier just to ask your teacher?

That was my thought too, then it struck me that perhaps the purpose of the exercise is actually to search for a mosfet part number, given the characteristics.

Some information to be aware of: https://youtu.be/GrvvkYTW_0k

Given the info you supplied, you’re looking for:

• an N-channel MOSFET (Vgs is positive)
• a Vds >= 60V
• a logic level gate (Vgsth ~1.5V)
• pulsed current >=40A
• Rdson <=20mOhm @ 5V and Id=36A

It’s probably overkill but a Texas Instruments CSD18533KCS should work for DC switch type operation.

If you want to to PWM a FET like this you’re going to have to provide more details.

Blackfin:

• a logic level gate (Vgsth ~1.5V)

My understanding, which may very well be wrong, is that a mosfet being logic level isn’t defined by a low Vgsth. That’s the voltage at which it’s guaranteed to turn off, not on.

It’s logic level-edness is defined by it having a suitable resistance at a logic level voltage on the gate:

Rdson <=20mOhm @ 5V

Correct me if I’m wrong, but that’s my take on it.

neiklot:
My understanding, which may very well be wrong, is that a mosfet being logic level isn’t defined by a low Vgsth. That’s the voltage at which it’s guaranteed to turn off, not on.

It’s logic level-edness is defined by it having a suitable resistance at a logic level voltage on the gate:

Correct me if I’m wrong, but that’s my take on it.

I believe (or always have, anyway) it’s the threshold at which a decent conductive channel forms. ON Semi says “This is the minimum gate bias that enables the formation of the channel between the source and the drain.” in their AN-9010.

I’ve generally used the rules of thumb (by correlation) that logic-level gates (a) usually have much lower threshold voltages and (b) lower Vgs(max) ratings due to thinner insulation layers that allow the weaker field from the lower gate voltage to produce a meaningful channel. Neither is an absolute of course, just an general observation.

RDSon resistance and the Vgs voltage for this resistance tells the story.

A low RDSon, <0.050Ωs, when Vgs is ~2 to 4.5V at a good high drain current will tell if the transistor can be an effective logic level MOSFET switch.

You will want to stay away from operating at the knee in the RDSon vs Vgs graphs.