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Driver for High Powered 3W, 5W LEDs Answered

Hey folks,

I am new to this LED thing.

I've bought around 90 high powered 3W and 5W LEDs with different forward voltages, and I am going to power them using some LED drivers that I bought with them. After searching for a while about how the nature of LEDs are, I am not sure about how should I connect these drivers to the LEDs because the drivers are constant current type of 1500mA, and the required amperage of LEDs are 700mA. I am thinking of adding one resistor to reduce 1500ma to 700ma just after + output in the series of LEDs line, but then because the drivers are a constant current one I think the resistor might just not work as the driver may try to push the current to reach to 1500mA so then it may ruin the resistor and LEDs afterward. Well, this is my guess and I am not so sure about that, so I need help with this one.

Here I bought 5pcs of the 50W type:


Above link is the drivers that I mistakenly bought from ebay (I could buy the 700mA drivers and make my life easy, but there is no high wattage (above 100W) with low amperage (700mA) LED driver in the market for a reasonable price for an unknown reason to me, could anyone answer this too?)

Also my another question is about the nature of LED drivers: Let's say there is a LED driver with a constact current of 700mA and output voltage of 30-45V and some LEDs with forward voltage of 3.7V and 700mA required current, what happens if I connect 4 LEDs to this driver? Does it ruin the LEDs for getting more voltage than required? Or it's gonna be fine because the current is constantly 700mA? I am so confused right now! Please help!

I also bought some temperature switches so I could add it to my circuit so I save my LEDs in case they got so hot! Yet I am not sure where to add them! If anyone could advise me on this I really appreciate it!



3 months ago

You need the 700 ma driver so you can put a number of LEDs in series which do change a little in forward voltage as the heat up and constant current is absolutely necessary so long as the total LEDs in series is less then the peak output voltage of the driver (could not read the driver spec)..

this driver has 1500mA, I already have it in hand and am looking for a way to reduce it's amperage to 700mA

Thanks for restating what I already knew by reading !

But I now understand how "locked-in" you are to using the 1.5A driver without the knowledge to do it !

This is about CURRENT SHARING and CURRENT SHUNTING application..

Simply shunt away 0.8 Amps to another load (see circuit image), in your case two constant current regulators feeding 400ma to three series LEDs each.. Now 1500 - 800 = 700ma..

There you are 700ma just for you :-))


Yes you put this in parallel with your LED string !

Thank you for that! I am just so noob and I don't really know what that LM317 is? could u explain more of that?

So this makes 6 LEDs run for 400ma, and the rest of the LEDs 700ma?

The LM317 is a fast hardy 1 amp regulator that can act as a constant voltage or current.

In addition this unit can only be damaged by a voltage in excess of 35v. If the unit gets too hot it shuts down until cool then restarts..

What else ?

Start 1500 ma less 400 ma = 1100 ma available

Now 1100 ma less 400 ma = 700 ma available..

Understand, that if you must use that 1500 ma constant current.

What is left if somehow you have a load that needs 800 ma ???

1500 - 800 = 700 ma that you said you wanted !

I can not be more clear for you.

1500 ma less the 700 ma you want.. Leaves 800 ma that must be wasted or thrown away..

must create a way to use up two low cost paths of 400 ma each totaling
800 ma leaving the available current which is 700 ma that you want to
power your load..

Did you also get heat sinks?

Not yet, I am thinking of the cheapest possible.

EE's don't like to hear this, and unlike what many think, I've been able to slightly undervolt LED's without limiting the current, while keeping them cool with a big heat sink and a fan. See what I did to SpectrumLED here: https://www.instructables.com/id/SpectrumLED-V20-t...

But you have so many LED's I would actually do it the "proper" way.