High Power LED Dimmer

[duda123]

Hello guys!
I'm trying to build an "Illuminator" for my video camera, since it's too expensive for me to buy, but I ran into some problems.
It will be made of 5 high-power leds and will have a dimmer and an on/off switch, but I couldn't find any high-power dimmer circuits on the internet. I'm a beginner in electronics. Can you help me, please?

This is the datasheet for the Leds i'll be using:
https://www.electro-tech-online.com/custompdfs/2012/07/LL-HP70MW6F.pdf

By the way, after this one I may build a 12-led one, and it would be great if you could help me with both projects!

Thanks very much for you support,
Eduardo

 

[ronv]

What voltage do you have for them?

Heatsink type?

 

[duda123]

As many 9v batteries as I need!
No heatsink yet!

 

[MrAl]

Hi,


Usually a PWM circuit is used to make dimming easier. It's not more efficient but it works good unless you can not stand any light fluctuation at all. A fast enough PWM frequency helps cure that too though.

If you use an actual buck circuit you get higher efficiency too which extends battery life for intermediate power levels.

 

[WTP Pepper]

I used 5 of these LEDs before on a project. A piece of trimmed copper clad board underneath sufficed as a heatsink with a touch of heatsink compound. They were individually driven by a ULN2803 driver. Each different colour was current limited with different resistor values as they has different forward voltage drops.
I drove the individual drives of the 2803 with a CPU using PWM to alter their brightness. The C8051F321 microprocessor can drive 5 independant PWM outputs under software control with no flicker.

As you are a beginner, try using an LM317K variable voltage regulator. Heatsink it as it will get hot. Google the LM317K part number, there are plenty of good examples out there.

 

[ronv]

9 volt batteries aren't the best for this because they have high internal resistance and low capacity. Give this a read. Basically with one battery per LED you might run for 1/2 hour.


https://www.powerstream.com/9V-Alkaline-tests.htm

 

[duda123]

Hm... I'll probably have some problems with overheating...
With if I use 36x 18.000MCD white leds (not high power leds)? Can you help me building a dimmer for it?

 

[ronv]

Sure. Let me see if I can find something.

 

[ronv]

How about something like this. $0.22 each at Mouser. How about a little battery holder for 4 AA batteries instead of the 9 volt one?

https://www.electro-tech-online.com/custompdfs/2012/07/C503B20WAN20876.pdf

 

[duda123]

Hm... I can use the battery holder!

But for the led, I'm gonna use this one, because I can't find here in Brazil the one you've shown me:
https://www.soldafria.com.br/led-5mm-transparente-acende-branco-18000-mcd-alto-brilho-p-2351.html
15.000 MCD to 18.000 MCD
Current: 20mA
Voltage: 3 a 3,2V

Is that ok?

 

[ronv]

PWM Dimmer

Sure that one will work.

Here is a schematic for a PWM dimmer. It needs a logic level FET because of the low voltage. I looked around at your site and didn't see one. If you can't find one we could use the TIP110 and a litttle heatsink.

 

[4pyros]

That my work, but just so you know most non branded LEDs will go dim vary fast.
The cheep ones can loose half its britness in a hour or so.

 

[duda123]

Hm... Is the logic level FET something like this?
**broken link removed**

4pyros, you mean they "life" will be reduced to an hour or so?

 

[duda123]

Ah! I've searched for that diode 1N914 on the website I sent you, but I couldn't find it! Can I replace it with this one (as they say on the website)?
**broken link removed**

And what does Rtot and Wiper stand for?

Thanks very much for your support!

 

[ronv]

Yes, that diode will be fine.
The Rtot and wiper represents a potentiometer like this one:
**broken link removed**
The center arrow is the center terminal on the part.

That site does not have any logic level FETs. There numbers would start with IRFL. They turn on at a lower voltage than the normal ones. Do you have another source for parts or should we change the design to fit a part on this site?

 

[duda123]

I've searched on another website from Brazil and they don't have FETs as well, so it would be nice if se could chance the design to fit parts from that website.
Thank you!!

 

[ronv]

Rev 1

We can change to a TIP120. I also slowed it down a bit because the transistor is not so fast and changed the base resistor and LED resistors to make up for the voltage drop.
Get just a small heatsink for the TIP120.

 

[duda123]

Thank you very much!

2 more questions:
1 - What does the "Rser" stands for?

You really helped me a lot! Thanks!
2 - How many Leds can I use without making changes to the circuit?

As soon as you answer me, I'll order the components

 

[duda123]

Ah! What's the voltage for C1-C4 and what kind of capacitor are they?
Thanks!!

 

[ronv]

Rser is just for the simulation it is the series resistance of the batteries.
C4 will be an electrolytic cap the others can be ceramic. Any voltage greater than 10 volts.