connecting LEDs to the driver

[aliyesami]

is there an ariticle detailing this ?
I was planning to do the following please correct me if iam wrong :

If I have a led driver say 24V @ 4Am max , I can connect 4 sets of parallel LEDs and and in each set about 8 leds considering the forward voltage drop is around 3V and max current rating for leds is 1 Amp.

since the driver is 4amp I will get 1amp max per branch .
am I thinking correctly ?

 

[alexan_e]

led driver say 24V @ 4Am max

What kind of supply is that?

Constant voltage, constant current ?

 

[aliyesami]

I think it said 'constant current' . but can you explain to me both the types? for what I mentioned which one would be applicable?

thanks

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this is the led driver that I want to use , please take a look, it gives ranges of current and voltage and its not saying if its constant current or constant voltage so how can I use it in my design ?

**broken link removed**

 

[alexan_e]

In a constant current supply the psu tried to maintain the total current to the specified rating as long as it can achieve it with a voltage up to the rated one.

If you connect multiple sets of leds in parallel you have no control of how the current will be shared in each brunch, some leds will have smalled forward voltage drop , some will heat more and this will effect the current

 

[aliyesami]

so if I want to have parallel sets of leds which setup is better constant voltage ?
can you please take a look at this driver and tell me if its constant current or voltage ?

**broken link removed**

thanks

 

[alexan_e]

Seems to be a constant current device

Constant current is better at driving leds, to equalize the currents you can use resistors

 

[Tunelabguy]

is there an ariticle detailing this ?
I was planning to do the following please correct me if iam wrong :

If I have a led driver say 24V @ 4Am max , I can connect 4 sets of parallel LEDs and and in each set about 8 leds considering the forward voltage drop is around 3V and max current rating for leds is 1 Amp.

since the driver is 4amp I will get 1amp max per branch .
am I thinking correctly ?

LEDs want a certain current to perform well. Too much current and they can be damaged. Too little current and they don't put out much light. The problem is that the amount of current is not determined very well by the amount of voltage. Both conditions of too much current or too little current can occur with a single fixed voltage across the LED. To counter this problem, LEDs are driven with either a constant current driver or through a dropping resistor, which also tends to regulate the current. Imposing a fixed voltage on an LED without either active current regulation, or passive current regulation through a dropping resistor is risky business.

When LEDs are in series, they obviously are all carrying the same current. So there is no problem with LEDs in series (except that the necessary voltage gets higher and higher the more LEDs you add in series.). But when LEDs are in parallel, there is no guarantee that they will share the current equally. That is 4 amps going to 4 strings in parallel will not necessarily result in each string taking 1 amp. It might be that one string takes all 4 amps and the other strings take none. That would be the case if the voltage characteristics of the LEDs were not well matched.

As a matter of practice, we do often see LEDs in parallel. They do share current fairly equally, provided the LEDs are themselves very well matched. They certainly should be from the same manufacturer, and ideally even in the same lot. That way you can count on the voltage characteristics to match so well that the parallel LEDs or strings of LEDs do share the current equally.

As to your specific question, are you sure that the strings of LEDs you have are just LEDs? Is it possible they have some built-in current-limiting resistor, or maybe even a current-regulating element? If they are only LEDs, then the above discussion applies. You should use a constant current supply, and hope the 4 strings are well matched to each other so that they share the current equally. If not, you will have to do something special to connect them all up.