ESP8266 LED Driver H801 aliexpress LED driver board.

[jeffeb3]

This thing has the drivers to move a lot of current at Vcc. There are some really detailed pictures on aliexpress. It says up to 96W/channel:
http://www.aliexpress.com/item/rgbww-strip-WiFi-controller-1-port-control-200-lights-communicate-with-Android-phone-via-WLAN-to/32301423622.html

The cool thing is that it has an ESP8266 inside, which can easily be programmed by soldering on some headers. I did it on the second try (after I switch rx, tx, d'oh).

This guy made the software even easier. That's the code I have on it right now. I have to just add the two white channels:
https://eryk.io/2015/10/esp8266-based-wifi-rgb-controller-h801/

So, I'm planning on just attaching an RGB strip that I have to the RGB side, but I also have some super bright white LEDs, that I'd like to use for this. I bought them without really thinking about how to drive them. I thought I could just use a resistor, but I'm finding that's not ideal because the LEDs don't really operate the way the smaller ones I have do. The ones I bought are here:
http://www.aliexpress.com/item/10pcs-3W-High-Power-LED-light-bead-emitter-white-Colors-led/1858307605.html

I found some solutions are to create a constant current power supply, which use an NFET for the big power, and an NPN for current limiting. This is where I first saw it:
http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/?ALLSTEPS.

My idea, which I'm hoping to get confirmation here, is to use the existing NFET (20N06l) and add the transistor and two resistors. I'm pretty confident I can do the soldering, but my knowledge of transistors and mosfets is generally "I can follow directions". Will this circuit work with the FETs that are on the board?

To be clear, I want to desolder the gate pin on the existing nfet, install a 1kish resistor in series, then just add the R3 and NPN transistor as shown in the instructable here:
http://www.instructables.com/file/FHYYUTRRCQEWP86JFY/

Another question, how much current would you drive through these cheapo LEDs? I was thinking 0.5A, because it's going to keep R3 near 1/4 watt. I have some 1ohm resistors that look big, but are of unknown origin (They came in a pack from my college electronics class).

Some more info: I've got a 6A 12V power supply, and I have 10 LEDs. I'm guessing I'll only be able to power 4 of them on each output, but that's probably OK. I have a 15V 2A supply, but I also need to power the RGB strip, and it's spec'ed at 12V. I'm planning on using this as a light for my fish tank. I'm hoping to start with just having a reliable timer on the lights, and then add stuff like changing the tint of the color when I get an email, or something. Just stuff that will drive my wife nuts, make my son go "woo" and make my friends laugh. The usual.

[jeffeb3]

After looking at this closer, I might be in over my head. I could definitely use some help.

- I looked at these NFETs when they are "on" and the gate pin has about 1.6V on it. I think that's why there is the level converter on the PCB, to make the 3.3V go to 1.6V.

- My "12V" power supply is actually producing 16V.

- I hooked up a 10 Ohm resistor, with 4 LEDs. Driving them with the NFET. So no soldering yet, just connecting the output. The voltage across the resistor was 0.34V, which indicates 34mA. The voltage across the NFET from D->S was 3.3V. Huh?

So it seems like the NFET isn't completely on, probably because of the 1.6V at the gate. That should be 5V, right? If I keep the 1.6V, then I don't think my NPN will work. I don't have 5V, but I have Vcc (16V). I guess that means I should use this circuit instead:
http://www.instructables.com/file/FV02PEYJ4VEWIFNTO8/

Maybe the 1.6V thing is to ensure the output is 12V? The voltage from VCC to the R pin (which is what I'm using to drive the LEDs) is 12.5V...

There seem to be many pieces to this puzzle I don't understand. Maybe this belongs in the beginner section .

[h3po]

According to the datasheet, that mosfet isn't going to do much at 1.6V gate to source. You're probably seeing the average of a PWM.
Arrange your white LEDs so that you end up with strings close to 12V and use conventional current limiting resistors. That is the easiest and cheapest solution if you still want to dim with the mosfet. Your power supply voltage will probably drop down close to 12V under load, don't worry too much about it.

[jeffeb3]

Thanks for the reply.

You were right. The PWM arduino code takes 0-1023, and the value used was a byte. As soon as you mentioned that, a lot of these symptoms made more sense.

The problem I think I have with a current limiting resistor is that if I have the LEDs strung up to around 12V, and the power supply is using 16V when there is no load, but down to who knows what with some load, how would I know what size resistor to use to limit the current to an acceptable range? If the voltage drop across the resistor is 3V, then I would want a 6 Ohm resistor. If it's 0.5V, then I'd want a 1Ohm resistor. The power disipated by the 1 Ohm is about 1/4W, which are the resistors I have, but if it's a 6Ohm, 3V, then I would need a 1.5W resistor, at least.

I did end up wiring it with the NPN controlling the NFET, and I ended up getting it to work, with 200mA measured for either 3 or 2 LEDs, which is good. But when I connected the 4th, the voltage wasn't enough, and it went down to about 20mA. That should have been higher, and I did tests with an open collector input to the circuit, and I was geting closer to 500mA, which is because of the PWM being set to 255, I'm sure.

I've also destroyed one of the NFETs, when I bent the pin trying to disconnect it from the PCB. But I think the original idea would have worked. The next thing I was going to try was to bypass the HC245 so I could control the pin as an open drain/open collector, but I bet you're right, I bet it's just not completely opening up the PWM.

Right now, I'm going to also test out driving it with an LM317, which I also happen to have one of. I'm hoping I can light at least 4 with one output. 5 would be better. Thanks for the tip.