12V RGBW Controller

Hi everyone,

Second post on the same subject, I'm not sure what happened to my first one. I

'm building a generic RGBW dimmer for automotive use, 12V max 6A, and was wondering if I might be able to get everyones opinion. I've been doing some reading on the web and I think that I've chosen the right components but would love to get some other eyes that are more informed to take a look.

IRF540 to power the LEDs
7812 to maintain 12V to the LEDS
7805 to power an Arduino Micro Board

I've didn't put in any resistors and it seems that I'm getting conflicting information when using the IRF540 on if I need them at all.

Would there be a better choice for components. Thank you in advance for any feedback.

IRF540 is not logic level MOSFET . You need either additional transistor to control IRF540 or use a logic level MOSFET like IRL540

Look at the RDSOn

IRF540N

LOGIC LEVEL MOSFET N-channel 60V 30A

You did not provide any link for the leds nor any schematic so I can't comment on your approach
other than to ask why you are specifying a 5V regulator when the Micro is powered from USB.

It concerns me that you have specified 6A led load and LM7812 (a 1A regulator) to power them.
This is a red flag . The first red flag was the IRF540 which is old technology. There are so many mosfets
with much lower RDSOn. The one I linked isn't anywhere near the best but it is overkill for your application. The fact that you have not posted a schematic or even the simplest drawing leads me to wonder if you are not possibly getting in over your head before learning the basics. I haven't seen anything in your post about PWM so I have no idea what you had planned. Since we are throwing it all out there I might as well ask you if you are even aware that you can get 64000 colors by combining RGB colors.

RGB COLOR CODES CHART

My next question is have you even tested a SINGLE RGB LED from your arduino using three PWM pins
and the codes from the above table ?
So for orange the table shows :
RED: 255
GREEN: 128
BLUE: 0

ARDUINO RGB LED TUTORIAL

I don't think you're there yet. You could use a little practice .

raschemmel:
Look at the RDSOn

IRF540N

LOGIC LEVEL MOSFET N-channel 60V 30A

You did not provide any link for the leds nor any schematic so I can't comment on your approach
other than to ask why you are specifying a 5V regulator when the Micro is powered from USB.

It concerns me that you have specified 6A led load and LM7812 (a 1A regulator) to power them.
This is a red flag . The first red flag was the IRF540 which is old technology. There are so many mosfets
with much lower RDSOn. The one I linked isn't anywhere near the best but it is overkill for your application. The fact that you have not posted a schematic or even the simplest drawing leads me to wonder if you are not possibly getting in over your head before learning the basics. I haven't seen anything in your post about PWM so I have no idea what you had planned. Since we are throwing it all out there I might as well ask you if you are even aware that you can get 64000 colors by combining RGB colors.

RGB COLOR CODES CHART

My next question is have you even tested a SINGLE RGB LED from your arduino using three PWM pins
and the codes from the above table ?
So for orange the table shows :
RED: 255
GREEN: 128
BLUE: 0

ARDUINO RGB LED TUTORIAL

I don't think you're there yet. You could use a little practice .

This is very helpful. Thank you. I know what the blocks should do but the actual circuity components within the blocks is where I fail. Always been more of a programer. So easy questions first.

  1. I do have a Arduino on a breadboard powering a single LED. The LED changes to the colors I want, when I want it too.
  2. The LED's dim while maintaining the desired color. Using a Potentiometer to choose the set the brightness
  3. Power Vcc will be from an automotive 12V battery (why I'm not using the micro USB port)
  4. I don't know the exact LEDs as they are already placed in the instruments, however they are powered with a generic controller
    like this: https://www.amazon.com/Eastchina-Strips-Controller-Designed-Flexible/dp/B00LXPCPTU
    Component List

12V 5A power supply (Supplies 12 V to LED strip lighting)
LM317
0.1uF Cap
1uF Cap
560 Resistor
4.7K Resistor

5V 1A power supply (For Arduino Micro)
7805

MOSFETs to control LED
FQP30N06L

Connector P5, P6, and P7 go to the OEM rheostat which is converted to a Potentiometer

Schematic attached below

"Close , but no cigar...."

LM317

You need to do your "due diligence".

The datasheet clearly states the operating current for the LM317 is 1.5A.

You need THIS

DC-DC converter ,input DC 8-40V ,output stable DC 12V ,Max.6A 72W

The Amazon page shows the controller listed at 3A, (double the rating of the LM317).

The schematic (aside from the LM317 part of course), still has issues..

You have the LM7805 OUTPUT connected to the Micro 9V INPUT (NO GOOD. If the 5V pin on the Micro is
the 5V OUT, and the 9V pin is the unregulated IN, then the 7805 is the WRONG part.
You should be using the LM7809, NOT the 7805.

FYI, to post a photo, upload the file, SAVE the post , then RIGHT-CLICK the attachment and select
"COPY LINK LOCATION",
then click the IMAGE toolbutton (looks like a picture) and paste the LINK LOCATION into the bar
and click save.

Use the LINK (chain link symbol) toolbutton to post links.

Sorry. I updated the post. The diagram for the Arduino Micro in EasyEDA does not show a Vin, where as the pin out does show it. I think that will fix the schematic except for the input power. Do you have anything that would make for a smaller package aside from the link to the item on Amazon. If I limited the output power to no more than 5A would that make it easier?

I'm guess an LM388 would work just fine instead of the LM317

Respectfully

What is it about 1.5A AUDIO POWER AMPLIFIER
https://www.google.com/search?q=lm388&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

that you don't understand ?

How does a 1.5A AUDIO amlifier solve your ned for a 6A 12V dc REGULATOR ?
What am I missing ?
Are we on the same page ?

Sorry I meant 338.

This one: http://www.ti.com/lit/ds/symlink/lm338.pdf

If you don't use a decent heatsink it will just burn up. You obviously don't realize how much 60W is.
Take an old fashion 60W incandecent light bulb and wrap it up with aluminum foil will a meat thermometer sticking inside and see how hot that gets. 60 W is STILL 60W and that's how much heat that LM338 will need to dissipate. Withou a good heatsink you have a recipe for disaster.
(ie your car catching fire and burning up ...)

I don't think you grasp the physics invoved.
The size of heat sink you need for 60W is ,
obviously 5/6 th the size of the 72W
DC to DC converter I linked, (83.3% of the size of the 6A regulator you said was too big).
As someone who does not grasp that you looked at the illustration of the LM338 and thought
"that's smaller, just what I want", but failed to factor in the size of the 60W HEATSINK you will need to mount it to,which if you don't will result in in the LM338 overheating and what happens
then depends on what you mounted it to.

There are a lot of things that I don't grasp (lol). I do appreciate your feedback though.

I knew I would need a heatsink, I just didn't think that I would need one that big.

I know on the controller that came with the lights it's connecting directly to the car battery and it's only 4.5cm x 3cm x 2cm. It's only rated at 12V and 3A (36 W) which still seems like quite a bit of heat to dissipate in such a small space but it never gets warm. I thought that I could eliminate any heat with heatsink that wasn't as large as the one you linked too.

I think I could eliminate the 12V Linear Power and just connect it straight to the battery (maybe that is what's going on inside the magic box as it originally came with a power brick), but I know that the power from an alternator can vary quite a bit up to 13.8V normally and I have seen it as 16V where the regulator failed.

I just want to make sure that that nothing goes pop, smokes, or worse.

The strip controller is probably a switchmode
supply. The LM338 doesn't say anything aboutswitchmode so it's probably linear, and
not as efficient.

I'm thinking of using the 12V rail on a computer power supply and regulating it down to 6V and split that into 3x LM338, each receiving 2 A.

Would it be tough to dissipate 12W? Right now I have these heatsinks, not sure how big i'll need them. My local store has some a bit bigger heatsinks.
TO220 Heatsink Vertical Mount with Pin - dipmicro electronics

can pretty much guarantee you that those are too small.
How to Size Heat Sinks for Semiconductors is a nice tutorial. Reputable mfrs have thermal resistance specs on all their heat sinks. Unfortunately, those are often not passed on to the consumer when they are sold by hobbyist parts vendors.

AAVID 5298 HEATSINK

Based on similar sinks I have used, I would guess ballpark of about 10C/W for those. Add the 4C/W for attaching a TO-220 to a heatsink, and your 12W will get your junction temp up to about 170C rise above ambient and they will cook (or go into thermal shutdown). You need a heatsink with a theta of less than or equal to about 5C/W to dissipate 12W in TO-220.

The AAVID 5297 in the attached reference in the post above mine MIGHT work but the 5298 would be better. Adding airflow would also be better.

bountyhunter said: ↑
Based on similar sinks I have used, I would guess ballpark of about 10C/W for those. Add the 4C/W for attaching a TO-220 to a heatsink, and your 12W will get your junction temp up to about 170C rise above ambient and they will cook (or go into thermal shutdown). You need a heatsink with a theta of less than or equal to about 5C/W to dissipate 12W in TO-220.

The AAVID 5297 in the attached reference in the post above mine would be about right. Adding airflow would also be better.
I think the number is closer to 2.5C/W, especially if you don't want to run the junction at 125C. It also depends on what your max ambient temp is.

Discussion about LM338 Heatsinks

x1222 said: ↑
I'm thinking of using the 12V rail on a computer power supply and regulating it down to 6V and split that into 3x LM338, each receiving 2 A.
...
Unless I misunderstood you, that is 6v*2A *3 which is 36 watts total.

That is more than just a heatsink issue, you now have a total device /enclosure etc needing to dissipate 36W!

To me, 36W continuous is a LARGE heatsink AND a fan, and an enclosure that is correctly ventilated for air flow AND located somewhere where it can source cool air and pump out all that nasty hot air.

Maybe if you say what you needed 6v and 6A output for, and what type of 12v 6A supply you have, we can suggest better options. :slight_smile:

Did you open up the box and see what is in the controller that came with the lights?

Yes I did. It appears to be just 3 MOSFETs and a controller.

IMG_3346.jpg

IMG_3346.jpg

The controller is the load (just a microcontroller and mosfets (probably low RDSON)

Each controller is rated for 3A@12V=36W *2=72W

You would need 1 LM338/PER CONTROLLER , (each a separate circuit because 2*3A = 6 and 6>5A(LM338 RATING), each TO-3 CASE, each on a heatsink

Maybe I’m looking at this wrong. Since this is in an automotive application where the battery normally doesn’t dip below 12V and shouldn’t get above 14V when changing maybe a buck converter would work better and just accept that when the battery drops below 12V the interior and instrument lights just turn off.

Also going back to the original boxes 3A max should make heat dissipation easier.

Hi All,
Am I missing something? We are running this off a 12 volt car battery, right?
Why do we need a 12 volt regulator for the LEDs? They do not need regulated
voltage. And besides, there is not enough headroom for a 12 volt regulator.
Run the LEDs directly from the battery!
Herb

I agree. I think you are more likely to have issues from the regulators than you are from running the strips right from the battery. The leds on the strip probably aren’t being ran at their maximum current rating anyway, and if you mount them to an aluminum bar or something similar that will help with the heat dissipation. If you don’t need them to be super bright you could also use a 24v strip...

Can't hurt to try.