WS2811B And MOSFETs

[Setrik_aZ]

Hi,
Recently I found this seven segment design by Electronoobs on YouTube which is a big seven segment. I used his schematics to make my own big seven segment and for testing the circuit, I made a PCB with 3 LED per segment and a dot point. here's my PCB:

The way it works, is using 3 WS2811 ICs which two of them control segments A ,B ,C ,D ,E ,F , and the other one controls the segment G and the dot point. obviously, the IC itself cannot deliver enough current to turn on the LEDs, so it uses 7 P-Channel Mosfets to drive the LEDs. and the dot point is connected directly to the IC.
Here you can see the original schematics:

And mine:

There's four differences between mine and the original, one is the number of LEDs per segment and one is that I connected the input VCC of the dot point to the VCC of the D segment. and I also used 100 Ohm resistors instead of 10 Ohm because my segments contain less LEDs, the other thing is the Mosfets, in the original design the Mosfets are SI2301, and in mine they're AO3401 which is the closest I could find to buy.

The code I'm using is the example code from Electronoobs himself, I put it in the attachments because its long and my topic will exceed 9000 characters limit.

So now lets get to my problem. When I connect the VCC and the GND to the input jack, ALL the LEDs turn on instead of the dot point, then when I connect the DATA pin, the ICs starts to sending output and their RGB pins turn HIGH and LOW and so the Gate of the Mosfets ( measured the voltage with a multimeter). But on the Mosfets Drain pin, nothing happens. its just changes from 0.6V to 0.5V which leads to increase and decrease the brightness of LEDs very very very slightly. The dot point on the other hand, which is connected to the IC directly, works fine and turns ON and OFF without problem.
So clearly there's something wrong with my Mosfets, but I have no idea what is going on and btw this is my first time using Mosfets.

Test Code WS2811 7seg.ino (10.4 KB)

[PaulRB]

You are switching the LEDs on the low/ground side. You should be using n-channel MOSFETs, I think, not p-channel, which is for switching on the high side. I don't know why the "Electronoobs" design uses p-channel, or why there are pull-downs instead of pull-ups on the MOSFET gates in that design. I'm not sure how that could work.

Personally I would have used tpic6b595 chips for a design like this, one chip per digit.

[Setrik_aZ]

PaulRB:
You are switching the LEDs on the low/ground side. You should be using n-channel MOSFETs, I think, not p-channel, which is for switching on the high side. I don't know why the "Electronoobs" design uses p-channel, or why there are pull-downs instead of pull-ups on the MOSFET gates in that design. I'm not sure how that could work.

Personally I would have used tpic6b595 chips for a design like this, one chip per digit.

I found the problem and fixed it.
The problem wasn't the p-channel or N-channel Mosfets, it was the connection, science it was my first time using Mosfets, I didn't know how to use them properly, and so instead of connecting the LED cathode to the source, I connected them to the drain, all I had to do was to switch the Drain and Source pin.
The reason why it uses P-Channel is that the WS2811 IC output is actually a LOW signal, which means that you have to connect the LED cathode to it not Anode.
But I really don't know what Electronoobs should do such a mistake! I'll surely contact him and tell him the problem in a few days and tell him to fix the schematics so other people won't get in trouble like me.