Can I use this MOSFET in my project?

Greetings all, I had a little PCB made which just did some PWM via a 10k Pot. I picked somethign easy because I just wanted to familizarize myself with using the arduino and then using the arduino as a programmer as I had programmed an ATTINY85 do do the PWM.

Afte rhaving the board made and sent to me it works! I'm totally into this! But the MOSFET (220 package) is pretty "tall" on the PCB and intereferes a little with turning the pot knob. So I went looking around and found this MOSFET that is in a DIP4 package ( http://www.digikey.com/product-detail/en/IRLD024PBF/IRLD024PBF-ND/812492 ).

So it SEEMS like it should work fine for my purposes: logic level gate, can handle 2.5 amps (I am using a regulated 5v supply in and my LEDs draw .8amps when turned "on" all the way). But I'm concerned about the fact that the MOSFET's data sheet says it can only handle "1.3Watts" as its "Max power dissapation." The other MOSFET says it can dissapate 75W! The "RDS" (which I thought was what you used as the "resistance" in any calculation on a MOSFET) is listed as 0.1 Ohm at 5v.

I tried to read some posts about how to calculate if this MOSFET can handle it and I came up with 0.1Watts which doesn't seem right and then a guy at work said he thought I needed 5Watts dissipation.

So I'm coming here to see if someone can tell me exactly what I need to find on a data sheet so I don't melt anything :slight_smile:

Again, my project has 5v regulated coming in, passing through the MOSFET (which is being triggered on the gate by the ATTINY85), and then out to the LEDs which draw about 0.8amps when fully on. These LEDs are in a piece of furniture so it's possible that they would be on full power "all the time" for days on end.

Thanks in advance if anyone can help me understand this because I'm really enjoying this and feel like I'm come so far and then BAM, brick walled because I don't understand this little piece.

ironspider:
So it SEEMS like it should work fine for my purposes: logic level gate, can handle 2.5 amps (I am using a regulated 5v supply in and my LEDs draw .8amps when turned "on" all the way). But I'm concerned about the fact that the MOSFET's data sheet says it can only handle "1.3Watts" as its "Max power dissapation." The other MOSFET says it can dissapate 75W! The "RDS" (which I thought was what you used as the "resistance" in any calculation on a MOSFET) is listed as 0.1 Ohm at 5v.

0.8 amps squared * 0.1 ohms = 0.064 watts dissipated as heat, unless I'm missing something. Of course I'm still on my first coffee of the morning so it's entirely possible.

The power dissipated in a mosfet used as a switch is the static power dissipation plus the dynamic power dissipation.

The static dissipation is I^2 * Rds(on) which in your case is 0.8 * 0.8 * 0.1 = 0.064W.

The dynamic power dissipation depends on how often you turn it on and off, how much current is available to drive the gate, and the total gate charge of the mosfet, and other things. The good news it that if you are switching at low frequencies such as the default PWM frequency of the Arduino or lower, the dynamic power dissipation is very low and you can ignore it.

So that mosfet is suitable for your application. Alternatively, look for a mosfet in an IPAK package such as the IRLU8726PBF. That will fit your existing circuit boards if you bend the leads out slightly, but it is shorter than a TO220 package.

Thanks!

For thae MOSFET referenced, it says

The dual drain servers as a
thermal link to the mounting surface for power dissipation
levels up to 1 W.

They obviously mean "serves".

@OP, FYI, many small parts qualify the power dissipation rating by indicating you need to
lay out a certain sized pcb copper area under the part, but this one appears to indicate the
mounting pads will suffice. You should be fine as far as heating goes.

Also, on the TO-220 packages that say "75W", this is only the case if you use truly massive
heatsinks. An un-heatsinked TO-220 package will start getting pretty warm with only 5W
or so dissipation.

Actually from my. Experience 1w is probably the safe limit without a heatsink, muc more than that and it will fry itself and burn your fingers

winner10920:
Actually from my. Experience 1w is probably the safe limit without a heatsink, muc more than that and it will fry itself and burn your fingers

You're probably a lot closer to the correct value, as the typical datasheet says
Junction-to-ambient = 62 degC/W