5x5 3W LED RGB matrix

Question

Hi, I'm new here

I'm planning to make the matrix using 15 N-channel logic level MOSFETs (three MOSFETs for each color in each LED), and 5 P-channel MOSFETs. The problems is, I can't seem to find a P-channel MOSFET (logic level) for a reasonable price.

It seems that the P-channel MOSFETs are a lot more expencive than the N-channel ones, what is the reason for this?

Does anyone know where I can find cheap P-channel logic level MOSFETs? Preferable a TO-220 packedge, I'm soldering them on a protoboard.

regards, Bjarne

Robert Peter Oakes · Accepted Answer

From what I can see on my cell it looks good

Test on a small scale first to confirm correct switching performance etc, then go from there

Good luck and let us see the results

Regards

Peter Oakes

Www.thebreadboard.ca

Sent from my iPhone

Robert Peter Oakes · Answer

I just did some digging and it seems the P channel ones are less available, not to sure of the reason but typically high side control is harder than low side to do as your typically switching voltages way in excess of the logic supply and this is typically gnd referenced based

you can use a reg P channel fet and augment it with an N channel driver or a simple NPN transistor to make life easier

refer to my blog about driving fets here: for some alternative driving tips http://www.element14.com/community/groups/internet-of-things/blog/2014/08/05/drive-big-things-with-added-safety-opto-isolators

if you don't need the isolation then you can substitute the opto darlington with a simple 2n2222 or similar

shabaz · Answer

Hi! For a given current rating, the P-ch uses up more silicon space than N-ch, i.e. they are physically larger, so less per wafer I guess! I'm no expert here on the manufacturing economics of them, but from old VLSI courses from memory, that's the reason why P-ch were more expensive traditionally. But to the point of your question, if you only need a few for a 1-off project, the cost is probably negligible compared to the rest of your project since they are less than $1 each. You would need to create your own driver using cheaper devices, as Peter mentions.