Help Using WS2811 to drive 12v RGB LED strip

Hi all!

Ok after some experimenting I tried using the logic level N-Channel MOSFETs I have (which are IRL540). I will try to post a schematic. From the outputs of the WS2811 I connected each to the Gate of the MOSFET. I connected the Source of each MOSFET to GND. Then as a simple test I connected the cathode of a LED to the Drain of the MOSFET and the anode to +5v. A couple of times the LED barely glowed and then nothing. I reconnected the LED back to the output of the WS2811 and the LED worked fine.

I could use some help. I did take a look at the guide on Adafruit's site and used the basic info there to apply the same circuit design to the WS2811 instead of the Arduino. I am not certain that the PWM mode of the WS2811 is working the same as the Arduino. Although it seems that it is in theory.

Thanks again in advance for any help!

With ws2811's, primary power is provided externally.  All you need from the control is clock, data and a comon ground. I control 30 with an Arduino Uno R3.

The Arduino only sends control and a clock information. It does not have to drive the LEDs. That done with a 2amp 5VDC power supply, which also powers the Arduino.

You are on the right track with the modfets, you will need three per Ws2811. The ws2811 has three outputs to drive all three LED colors.  This way you can effectively increase the current carrying capabilities of the  WS2811s and a common supply can be used.

Make sure limiting resisters are used.  Chech to see if the ws2811 is not satisfying the mosfet. You may need an isolation stage between the two.

Have you tried to trigger the mosfets without the ws2811 connected.  Also, since the color intensity is controlled by PWM, is it possible mosfet can't keep up and the result is a dim LED?

-Steve

With ws2811's, primary power is provided externally.  All you need from the control is clock, data and a comon ground. I control 30 with an Arduino Uno R3.

The Arduino only sends control and a clock information. It does not have to drive the LEDs. That done with a 2amp 5VDC power supply, which also powers the Arduino.

You are on the right track with the modfets, you will need three per Ws2811. The ws2811 has three outputs to drive all three LED colors.  This way you can effectively increase the current carrying capabilities of the  WS2811s and a common supply can be used.

Make sure limiting resisters are used.  Chech to see if the ws2811 is not satisfying the mosfet. You may need an isolation stage between the two.

Have you tried to trigger the mosfets without the ws2811 connected.  Also, since the color intensity is controlled by PWM, is it possible mosfet can't keep up and the result is a dim LED?

-Steve

Yup, there pretty straight forward to control, look at my profile picture, that’s a string of WS2812B’s controlled from an UNO and a batter for when I go to hacker nest events and the like.

I will open up the circuit and code and share soon if you like

Peter

You do have a cool hat band. The code I used originally appeared at adafruit. I'll dig some pics as well.

-Steve

Thanks Steve. I have not tried to trigger the MOSFETs yet, but that was my next plan. I should be able to do that by applying +5v to the Gate and connecting the Source to GND. I should see voltage flow between the Drain and the Source using a resistor or LED as a load. The data sheet indicated that the switching speed should allow me to use this for PWM.

I am looking for just a WS2811 so I can post what I have.

Thanks in advance,

Don

Make sure you connect a ~1K – 10K resistor between the gate and the device driving it, MOSFET gates have a relatively high capacitance and you can get a lot of ringing without the resistor. I found this out through experimentation for my power supply (Yes I ignored all the literature and ended back there anyway ) you will also generate less interference this way too ans the edges are shortened

Peter

You can't put much resistance in the gate circuit if you want the MOSFET to switch fast - which you will if you need a high efficiency switching circuit. Lots of MOSFET drivers offer currents in the 1-5 A range and you couldn't do this though a 1k resistor.

I

Here's a little demo. It's a nice crude boost switcher. Try varying R2 up to 1k and watch the current in L1. (simulate with LTspice).

The operating frequency is only 100kHz but it is a nice low on resistance (so high gate capacity) MOSFET.

MK

I completely agree if I were making a buck / boost regulator or a high frequency amplifier but in this example were at best providing PWM at a few hundred hertz to a string of LEDs, or even simpler, just using a MOSFET to switch them on or off. If it was to be switched at hundreds of KHz or Mhz then I would be reducing the resistor or having a very very hot MOSFET as it would be forever in its linear region

In this case you do want a slightly slower switch on time as this will prevent EMF, ringing and other transients on the wire and will be less stressful to the circuit overall and of course a uController can not provide the current to a MOSFET gate at the rates of hundreds of milliamp or more.

In this case it is more for slew rate control than fast switching times and a value of about 10K works great, I even tested this on the bench in the past and is what I am using on my bench power supply for driving the P or N channel MOSFETS

What are the MOSFETs doing in your PSU - I'd assumed they were switching but from your comments probably not. Have you posted a circuit somewhere.?

MK

There will be soon posted to the Power Supply project on E14 and on YouTube

I'm not building a buck / boost converter but  a modular linear bench power supply, the MOSFETS have way more power handling ability that the BJTs and almost the same drive circuits in most cases