Better P-Channel MOSFET?

I am recreating an old PCB that has long gone past its usable life. It has many MOSFETs on it. From over the years it looks like some of them have got hot enough to change the color of the PCB surrounding them. Years of use and Load, heat dissipation, thin PCB. Appear to all be factors.

I read somewhere, possibly the datasheet of the regulator used in the popular buck converters. The very popular 2596 (LM2596?), is able to regulate voltage with little to no heat dissipation.. I was wondering if anything similar has happened with MOSFETs?

This board uses a P Channel, "RKB" SOT223 package. I can't seem to find that particular marking but it appears to be a general purpose 3Amp MOSFET.

The fets drive 12v incandescent lamps, maybe up to 2. Just to get an idea of the load.
I do not know the wattage... guessing 3 watts? It is the type of bulb you would find in old school car turning signals.

Anyway, as I remake this, was just wondering if anyone knew of newer, better performing general purpose P channel FETs in a SOT223 package.

ALSO, will making the PCB thicker help with the heat?

What is the voltage applied to the MOSFET gates ?

Measure the amp draw of a bulb.

Draw and label the schematic circuit and show it to us.

Some examples of MOSFETs:

Sure, MOSFETs have improved in the past decade. But not that much... more likely the design was over optimistic.

Maybe an old analog regulator instead of nowadays switching power supplies?

hahaa A big ol' Torrid and a bridge rectifier. awesome.
I miss the days of lit buttons, idiot lights (not led driven), big toggle switches.

I think you're both right. This is a multi-purpose board. There are fets on here that are not used in its current configuration. Driven by a PIC. woo hooo. So it is about the year 2003. Y2K compliant. Geeze, remember that one?

Back into my DeLorean....

did you maybe mean, "toroid"?

Gate voltage is 5v.

The regulator to drive the logic can go up to 35v.
It was made for 12v but might as well make it 24v friendly.

Thanks for the PDF. You didn't make all those yellow highlights did you?

Some of these look amazing.

That said, the AO3401 might work, different package too The footprint of the PCB is important to maintain. Those just seem so small. The dissipation .. highest thing there is 70c , that's not bad, right? I've never paid attention until now.

AO3401 looks promising! Wow, cheap too!
Should I use these?

Well those have 12v gate, so no.

“ You didn't make all those yellow highlights did you?”


Those are important items for logic level applications.

Google original data sheets for more information.

Vds(max) will be the voltage you can switch.

Limit Vgs(max) with a zener or resistor divider.


Thank you!

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