Difference between Drivers and PSUs??

[Steviecuk]

Whatbos the difference between an LED 'driver' and a 'PSU'? I have been steered towards some divers to power some 3w 3v 900mA Cree LEDs (link below) but they still require the equivalent power input from a PSU. So what does the driver actually do?

http://pages.ebay.com/link/?nav=item.view&alt=web&id=171621025965

 

[tazz]

A psu supplies power at a constant voltage with a varied current as required.
A driver supplies a constant current over a select voltage range.

LED`s require a driver to operate correctly.

 

[Steviecuk]

A psu supplies power at a constant voltage with a varied current as required.
A driver supplies a constant current over a select voltage range.

LED`s require a driver to operate correctly.

Thanks Tazz.

I have an old PSU from a PC which I would like to use if possible. Now I know they have multiple 12v outputs, and the consumption needed will be somewhere in the region of 36v (12x 3v LED), is there any way of wiring this PSU to the constant current driver to deliver the 36v?? Ie connect 3 sets of 12v outputs from the PSU to the driver?

Cheers mate.

 

[baldsparkies]

This video may be useful

https://www.youtube.com/watch?v=ApQt1rz8urU

Don't forget you need to connect the green and black wires together as shown to get the PSU to work.

 

[Steviecuk]

This video may be useful

https://www.youtube.com/watch?v=ApQt1rz8urU

Don't forget you need to connect the green and black wires together as shown to get the PSU to work.

Thats brill, thanks. Will three yellow 12v from the PSU wires connected together and soldered to the inputs on the driver provide it with 36v or will it just go bang?

 

[baldsparkies]

Thats brill, thanks. Will three yellow 12v from the PSU wires connected together and soldered to the inputs on the driver provide it with 36v or will it just go bang?

The PSU will probably see the separate output connections as a short.
As a suggestion it may be possible to connect diodes across the outputs to solve the problem, but wait to see what others have to say, or put the question to a good PC repair centre, they should know.

 

[tazz]

Do not connect the yellows together.
As from Baldsparks video link, wire 3 x leds in series, with limit resistor(value dependent on fw current of led) and wire 4 of these in parallel with the yellow & black psu cables.

 

[baldsparkies]

One other thought, it may be worth using a volt meter across two of the 12v outputs and see if you actually get an increase in voltage, ie 24v.
I have a funny feeling that although you may have separate output taps, they are supplied from a common source at the transformer.

Sorry Tazz,
I was typing whilst you posted, question is answered.

 

[tazz]

No transformer, its switch mode. Each output is also current limited

 

[Steviecuk]

Thanks guys. Do you mean like this?

[url=http://postimage.org/][/URL]

Would this need the 'driver' then?
This would be ok running from one single 12v supply I presume? And if one of the LEDs burned out, the resister would protect the others on the circuit from overloading correct??

 

[tazz]

Spot on.....last thing we need to know is led spec...3v but need forward current is it 30mA....we can then tell you resistor required

 

[Steviecuk]

They are quite high powered LEDs by cree.

http://www.ledgroupbuy.com/cree-xm-l-white/

wattage:
2.1w (700mA), 3.1w (1,000mA), 5w (1,500mA)

max drive current:
1500mA

forward voltage:
3.0v (700mA), 3.15v (1,000mA), 3.3v (1,500mA)

luminous flux (cool white):


244lm (700mA), 327lm (1,000mA), 424lm (1,500mA)












There will be various colours but I'm guessing I can do the same thing with other 12v yellow wires from the PSU and just have several loops?

 

[Steviecuk]

One other thing though, I will need to have some sort of dimmer on them. I have seen these which I am hoping will work and can be but straight after the PSU.

DC 12V 8A Adjustable Dimmer Switch Control PWM Controller Single Color LED Strip | eBay

 

[tazz]

Yes any pwm will work fine

 

[Steviecuk]

So would this plan work with the LEDs that I linked to? Any without needing a driver?

 

[tazz]

Yes should be fine, computer psu (12v) pwm to control brightness,

 

[Steviecuk]

Brilliant thanks Tazz.

 

[Steviecuk]

What resister rating would you recommend using on the above spec?

 

[tazz]

As previous, what is the led specifications...?

 

[telectrix]

if 1 LED went open circuit, the other 2 in series with it would go off.