Quote Originally Posted by Ioannis View Post
Obviously I mistyped the part number. Yes it is a P channel.

From the datasheet the Vth seems to be 4Volts min. Have you tested yet this MosFet? ...
Nope. But I'm using a IRFZ44N n-channel to PWM the LED strip with has similar specs.


Quote Originally Posted by Ioannis View Post
...Please check with an Osciloscope that the MosFet is fully closed at PIC low state, so that there is no voltage drop on S-D pins....
Good idea. Choosing the proper resistors to drive the MOSFET is still a black art to me.


Quote Originally Posted by Ioannis View Post
...Was there a specific reason that you selected a P channel instead of a N channel control of the PWM signal? Usually the N channel have better characteristics in terms of Rds.

Ioannis
Because when I first started testing blue-on-white LCDs, I was PWMing both the Contrast (V0) and Backlight (LedA). I didn't even consider MOSFETs and went straight to transistors since we're not talking about a lot of current. Why I chose PNP transistors back then is a mystery; maybe I saw a schematic on google and copied that.

I've since switched to white-on-black LCDs, I don't need to have adjustable Contrast (V0). So controlling the Backlight with a PNP transistor is just "the old way of doing things". But since noise has become an issue, getting a P-channel MOSFET seemed like the logical way to replace the PNP.

But if I had thought about it for 2 seconds, I would have realized I have access to both the Anode and Cathode on the Backlight. Since I already have an IRFZ44N on the circuit, it would cost less at JLCPCB to use another IRFZ44N instead of a second type of component.

So that's the long-winded way of me saying that now I'm going to swap the 2N2907A PNP to a IRFZ44N n-channel.

Funny story, I finally realized the letter at the end of a MOSFET seems to indicate the channel. I don't know if it holds true for all, but it's working for the first two that I researched.