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Topic: High power leds and led strips (Read 5413 times) previous topic - next topic

outro

#15
Feb 20, 2017, 07:47 pm Last Edit: Feb 20, 2017, 08:47 pm by AWOL
So, the mosfet heats up because of the higher voltage supply, and not the PWM.
And because with the "linear" PWM the current goes quickly up and down, this creates the heat
Thanks so much for clearing this up! I think I finally got it!

I mix and match. Sometimes a article is cheaper or available in more versions from one of the two. Just look at both although I must say, past year I ordered more from AliExpress then eBay.
Thanks for the tip. Decided to order from alibaba 10pcs-10W-LED-Driver-for-3x3W-9-12V-900mA-High-Power-10w-led-chip-transformer-for

Do you think there is something else I should know or some other resources I should take a look at?

I think you have it.
When switched on or off little heat is generated.

When operated between 0 and 100% it is operating in the linear region where significant heat is generated.
During switching it is operating in the linear region and generating heat,, but because the switching time is so fast it is not in the linear region for long.

An oscilloscope is not essential but if you want to build a circuit using discretes it is a very useful tool to see what is going on.

Most of us had to wait a long time when we started out to get one.
I built my own (from a kit.)
Thanks for your post
About the oscilloscope, I am VERY impatient when it comes to things. This ones an analog 30Mhz (quite old) oscilloscope so I have to upgrade (when I know I really need one, better).
It was either this, or one "nano"/portable/diy. I decided to go with the analog because I think I'll learn more this way!

Moderator edit: tags corrected

septillion

AliExpress ;) AliBaba is the greater wholesale brother of AliExpress.

Only one problem, you ordered 900mA (or 1000mA depending on which part of the description you believe) drivers but the leds you showed had a max rating of 700mA...
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

outro

AliExpress ;) AliBaba is the greater wholesale brother of AliExpress.

Only one problem, you ordered 900mA (or 1000mA depending on which part of the description you believe) drivers but the leds you showed had a max rating of 700mA...
Oh dayum! I thought the leds pull what they need?
Is there something I can do to fix this?

septillion

No, that's the whole point with leds, you have to drive them with a current hence the current source ;) That was the whole idea of the driver.

There are two things you can do.

1) Replace the resistor on the board that set's the current. It's a very low value resistor. On this board you're kind of lucky. To get to close to the desired value they used two resistors in parallel. A R330 or 0,33Ohm and a R200 or 0,20Ohm. The formula for the current is 0,1 / R = I. So 0,1 / (R330//R200) = 803mA. So the claimed 900mA is a bit high. But 800mA is still to much. You can replace the resistors to get to 600mA (to stay save) but then you'll need 0,17Ohm resistor in SMD. Or, you can just remove the R330. This leaves only the R200 which gives you a save 0,1 / R200 = 500mA.

2) Buy a new set and put these in your stock :D
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

outro

#19
Mar 14, 2017, 12:34 pm Last Edit: Mar 14, 2017, 12:40 pm by outro
...You could also make a linear current source with transistors which is a lot better then a resistor (who wants a 7W resistor) but that transistor will still produce A LOT of heat.
Whaaaa, now I see my quote again I see a terrible typo! Edited the post and here it's correct again:It's a little module. Some links:
PT4115 900mA
PT4115, probably 600mA, not 100% sure, listing is a bit weird
Probably PT4115, 300mA
...
I have now received the 900mA version of this, and was thinking, is it possible, some easy way, to limit the current other than changing the resistor? I do have a lot of different resistors, both 1/4W and 1/2W

Also, I am not quite sure how to use this? It has only GND + Vcc? Should I stick it in between of a circuit? How can I control it with an Arduino?

septillion

is it possible, some easy way, to limit the current other than changing the resistor?
Simple answer, no.

But you could go for the "remove R330" option to make it a 500mA module.

Also, I am not quite sure how to use this? It has only GND + Vcc?
It certainly has not! It has two wires labeled "Led out" which go to the led. And at the other end it has two pad's for the supply voltage. It has a bridge rectifier on it so polarity doesn't matter.

How can I control it with an Arduino?
Told you that already ;)
I think all these three are based on the PT4115 chip which is a very popular chip. Although most modules don't break the pin out (aka, don't add a solder pad) the chip does support dimming via PWM. Just solder a wire directly to the chip and it's a very easy driver.
It's pin 8 of the chip aka the one next to the word "OUT". You can connect this pin to an Arduino pin. And of course the led GND and the Arduino GND need to be connected.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Jiggy-Ninja

#21
Mar 15, 2017, 03:21 pm Last Edit: Mar 15, 2017, 03:23 pm by Jiggy-Ninja
I googled a more accurate picture:

And does the "crazy" heat come from the PWM?
The "crazy heat" comes from ignorant fools (like whoever made that schematic) persisting in using THE WRONG KIND OF MOSFET for their design. For an IRF540, the RDS(on) is only provided for 10V VGS, which gives you a hint of what kind of gate voltage this was designed for. They don't even provide graphs for gate voltages less than 4.5V.

A quick test in the datasheet is not the Gate Threshold Voltage (VGS), but the Static Drain-Source On-Resistance (RDS(on)) spec. You can get a rough idea of what kind of gate voltages a MOSFET was designed to be used for by what gate voltages this spec is provided for.

For example, even though the FQP30N06L (attached) does not state anywhere in the description that it is a logic level MOSFET, it provides an RDS(on) for both 10V and 5V. So this would be a suitable MOSFET to consider for a 5V system, but 3.3V would be pushing it.

On a more extreme end, the DMG6968 (attached) provides RDS(on) specs for 4.5V, 2.5V, and even 1.8V gate voltages. This would be an excellent FET to use for moderate currents in a low voltage system.
Hackaday: https://hackaday.io/MarkRD
Advanced C++ Techniques: https://forum.arduino.cc/index.php?topic=493075.0

outro

#22
Mar 15, 2017, 09:02 pm Last Edit: Mar 15, 2017, 09:46 pm by outro
@Jiggy-Ninja, thank you for your explanation, I didn't know about this DMG6968, have to take a better look at it !
@septillion
I think I will solve my problem(s) with buying the following item(s):
http://www.ebay.com/itm/272502198541?var=571562633572

http://www.ebay.com/itm/401089836411?var=670618877036

I wanted to consult from you though, what do you think? Do the prices seem high & should I just roll with the 500ma? I did a small test, 700ma vs 500ma , the change is not that big, or I don't notice it.

Attached pictures
(pic: 887 in 500ma)

Jiggy-Ninja

If you take a careful look at that driver board, you will see that it has a PWM input near VIN+. You don't need to switch power with a MOSFET.

Perception of brightness is highly nonlinear. Changes in intensity are much more noticeable when at brightness than high. It's the same as our perception of loudness.
Hackaday: https://hackaday.io/MarkRD
Advanced C++ Techniques: https://forum.arduino.cc/index.php?topic=493075.0

septillion

I would indeed say 12 pound is on the high side for 10.

And if you use a module with a PWM capable chip you don't need a external mosfet :)

And yeah, I would go for 500mA now. Like Jiggy-Ninja said, our eyes are not linear and even a LED is not linear all the way. So yeah, the gain isn't that big. And two extra pro's for the 500mA: your leds will life longer and will require significant less heatsink :)
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

outro

Thanks for the answers, decided to skip buying those (for now at least!)
My last dumb question is, after desoldering the resistor, do I have to connect the removed part?

septillion

What do you mean by "connect the removed part"? Do you mean, bridge the solder pads? Then NO, then you'll blow the led. Like I said, it has two parallel resistors, just remove the one and done!
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

outro

What do you mean by "connect the removed part"? Do you mean, bridge the solder pads? Then NO, then you'll blow the led. Like I said, it has two parallel resistors, just remove the one and done!
Exactly what I meant , thanks for correcting me !

If you take a careful look at that driver board, you will see that it has a PWM input near VIN+. You don't need to switch power with a MOSFET.

Perception of brightness is highly nonlinear. Changes in intensity are much more noticeable when at brightness than high. It's the same as our perception of loudness.
I started working on the board now, and I can't find the PWM input near VIN+ ?
Are you referring to my 900mA driver?

I think for the PWM I need to solder pin 8 of the IC near the outs?

septillion

I started working on the board now, and I can't find the PWM input near VIN+ ?
Are you referring to my 900mA driver?
He wasn't ;) The other module you showed had the pin broken out. The one you have don't.

I think for the PWM I need to solder pin 8 of the IC near the outs?
Exactly! See reply #20 ;)
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

outro

He wasn't ;) The other module you showed had the pin broken out. The one you have don't.
Exactly! See reply #20 ;)
Alright, I'm almost there!
This is very amazing.

I had some trouble getting the R300 off, (see images) but I managed.
I hope I didn't manage the board (quite a lot of heat...)

See pictures for reference :)

* I was able to get it off easily by adding a lot more solder and then using the 'solder sucker' to get it off

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