Help finding right MOSFET

I'm hoping someone on here might be able to help, I'm currently using this MOSFET

for PWM'ing 12V LEDs in a project.

I'm curious about stepping up to being able to use 24V LEDs as well as 12V and was hoping someone might have a part number on hand for a small MOSFET (ideally in a SOT23 casing) that can handle a max voltage above the 24V, and has suitable properties for running via PWM.

Thanks :slight_smile:

Looks like you’ll have to move to a bigger package. If you need more than one
be aware there are dual MOSFETs in SOIC8 package like: http://canada.newark.com/vishay-siliconix/si4910dy-t1-ge3/dual-n-channel-mosfet-40v-6a/dp/26R1895

I may have to abandon the notion for the short term, there is not a large amount of space currently on the board. If I find a suitable MOSFET I'll have to move some things around I think.

What I'm not fully understanding about n-channel MOSFETs is the effect of the On Resistance on performance. Currently PWM signal is coming from an ATMEGA328P at what I believe is 500Hz, and 8 bit, and a 5v control voltage. When I look for MOSFETs to handle 30v I seem to have a hard time finding ones with On Resistance in the same ballpark as the one I am currently using in my projects. Would someone be able to explain basically what my trade-offs are in regard to the On Resistance. My understanding was lower resistance less energy wasted when the MOSFET was conducting, but am I also trading switch speed at the same time?

Thanks for the help.

On power loss = I-squared-R, so lower R means lower dissipation. Double the current
and you ideally want 1/4 R.

Higher voltage FETs have more capacitance for a given Ron, or put another way
higher Ron for a given capacitance - this is really just the geometry of the channel
manifesting itself - higher voltage = longer channel = more resistance. You can
make the channel wider to reduce resistance, but that increases gate capacitance too.

(Its actually rather more complex, power MOSFETs have vertical current flow)

Is this in the right direction?

I dunno.

That looks like a good choice.
You're not actually running 30V thru it, yes? Some lesser amount, like 24 max?