I am giving myself a headache with this one..

I need to power an array of 9

They are rated at 700ma, 3.2v

With an array of 9..thats just over 20w...


There are plenty of constant current 230vAC modules that can handle these LEDs... but for £60 thats a bit steep for a prototype....

How can I power the LEDs? Its just a simple lab type test for the time being, so I dont want to spend lots until I am satisfied that the LEDs will do the job required of them...

I dont have a suitable DC transfomer... so assume that the supply is 230vAC


Can anyone help?

[Edited on 12/2/10 by tegwin]

How are they wired? Series or parallel?

You can always just use a 6v lead acid battery with a voltage regulator

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5339319

or:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5456391

Not A voltage Reg on diodes

You need a current reg as Tegwin says.

Don't go letting the smoke out

[Edited on 12/2/10 by Doofus]

Hmm...

That might work as a constant voltage for testing...

But ideally I need constant current at 700ma


I have not wired up the LEDs, so could be either series or parallel...


This is a very basic constant current reg... but I dont think it would work for 6000ma..

http://www.discovercircuits.com/PDF-FILES/CONSTANTCURRETLED1.pdf

[Edited on 12/2/10 by tegwin]

Mobile phone battery 3,7 volts 1000mah same thing as a single cell lipo battery

its current opperated, not voltage, going to need something like a resistor in series there chap.

or just leave it how it is and have very bright LED's, for a short period of time.


[Edited on 12/2/10 by graememk]

4 Ohm resistor on a 6v bat (or regulated supply/transformer) would do.
2w though

[Edited on 12/2/10 by Doofus]

Hmmm...

If I use a 12V battery....

Connect the LEDs in three parallel rows of 3 series LEDs... Then each series row would need a 2.2ohm 1W resistor

not an ideal solution... But would be the cheapest way for testing perhaps..

Solution 0: 3 x 3 array uses 9 LEDs exactly
+----|>|----|>|----|>|---///----+ R = 2.2 ohms
+----|>|----|>|----|>|---///----+ R = 2.2 ohms
+----|>|----|>|----|>|---///----+ R = 2.2 ohms

The wizard says: In solution 0:
each 2.2 ohm resistor dissipates 1078 mW
!! the wizard thinks the power dissipated in your resistors is a concern
together, all resistors dissipate 3234 mW
together, the diodes dissipate 22050 mW
total power dissipated by the array is 25284 mW
the array draws current of 2100 mA from the source.

If you're going to be messing around prototyping stuff just get yourself a bench power supply with current limiting.

Not that cheap but its useful for a load of stuff.

I'm sure there are some second hand units on eBay etc?

you saying you want the leds powered off the mains?

or the mains is there to provide a power, whcih may need some additional conditioning?

and do you want to power one or how many at the same time?

there are a number of ways to do this.

you can use a drop resistor with the mains - I did this with a teeny 5 mm LED but resistor can get hot.


these 700 mA led sound like LED emitters.

the most efficient way to drive these is by using a constant current driver - read my atcile on DIY LED lamps.

look on ebay for teap0t42 items,

see


these take a input voltage 7-24 V; so if you have an RC toy, use the battery from that or use car battery.

else get a mains power supply for that voltage range.

BTW I have some less 3 W (that one is 5 W) drivers that I don't need - make me an offer .....

quote:

---

Originally posted by tegwin
Hmmm...

If I use a 12V battery....

Connect the LEDs in three parallel rows of 3 series LEDs... Then each series row would need a 2.2ohm 1W resistor

blah blah ...

---

quote:

---

Originally posted by tegwin
Hmmm...

If I use a 12V battery....

Connect the LEDs in three parallel rows of 3 series LEDs... Then each series row would need a 2.2ohm 1W resistor

---

Sounds simular to the led drives I made for a brother.

LED Bike lamps using a 3 amp drive IC controlled but a PIC microcontroller.

Will drive any constant current upto 3Amps.

this type of PCB should be able to drive 3 in series (11v approx) and 3 set of these in parallel (2100ma) (9 in total).



input 7-24V.



LEDLAMP1


used for this type of lamp


Lamps


For simple tests a power resistor to set the current.

Martin