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What driver/ power supply do I need to wire up two 12v led MR16 bulbs? Answered

I am designing and making a lamp for a technology project at school and after doing lots of comparisons found these bulbs which seem to have a good spec.

Mr16 LED DC 12v 3.8w 270lm White

I wish to have two of these bulbs wired up with separate switches so that I can control them independently, how do I wire these up? Do I need a special lighting/LED driver or will a standard AC-DC 12v transformer (wall wart) suffice?

If so can anyone recommend any that will do the job and post a link. I would also like to go for the most affordable option.

On the bulb webpage this 20W Variable microdriver LED driver is recommended for someone wiring up 5 bulbs. is this overkill for what I want?

I am ordering the bulbs from rapid online so if they sell something suitable please link me to that.

Thanks to anyone who can help me.


I think these lamps come with a constant current driver of some kind already built in to them.

In the data sheet I found here:
there is a somewhat cryptic blurb which reads:

"With  rated  voltage  &  constant  current  drive  IC,  offer  constant  brightness  against unstable environments."

The way I interpret this blurb is that it is saying the lamp comes with a constant current driver.  Moreover this driver IC singlemindedly works to keep the current to its LEDs constant, in the face of a supply voltage which may be changing somewhat. 

Another way to interpret that blurb is that it says: You must use this lamp with a constant current drive IC.    But I don't think that's what it says.

I think this thing is intended as a drop-in-replacement  for a halogen lamp that is the same shape (i.e. MR16), and that suggests you just hook it up to a 12 VDC, or 12VAC, supply, without a driver.

Also in the comments on that page you linked to,
someone asked if it was dimmable, and the answer was no, and that answer would be consistent with LED lamp with a truly constant current driver.  I.e. the regulator tries to keep the LEDs supplied with constant current, even in the face of fluctuating supply voltage.  So trying to dim it, i.e by reducing the input voltage,  would just be fighting against the regulator.

BTW, to add to the confusion,  constant current drivers that are dimmable exist too, but they do this "adjusting" their constant current output, which means maybe it's not strictly "constant", or only constant in a more narrowly defined sense.

Final note:  I think when Steve answered this question previously, he was incorrectly assuming this lamp does not come with its own regulator.  Hence he is recommending you build a constant current regulator, and that's what the circuit with the LM317 is. 

I think all you need to power those lamps is a 12 DVC, or12V AC, source capable of supplying the required power, which works out to about 300 mA, per lamp, in terms of current.  So if your wall-wart, or transformer, is  rated at around 1 ampere (1000 mA) or more, that should be sufficient to power two lamps.

If I'm right, these lamps will be somewhat hard to break electrically.  The on-board regulator will go a long way towards protecting the LEDs, and probably the only way to break the thing would be with excessive voltage, like accidentally plugging them into the 110, or 220VAC, or whatever the mains voltage is where you live.  

I contacted the tech support at rapid and they said that they would say that the bulbs will run at their optimum brightness if used with a rated voltage & constant current drive, but they would obviously still work if it was fluctuating slightly, just not to their potential.

So a 12vDC psu will work fine, one that supplies 1A will power two, and although i'm guessing that it won't give constant current, going on th fact that i'm only drawing 600mA total out of 1000mA available it would have to fluctuate a lot for the bulbs to operate at anything but near optimum.

Your thoughts?

Well i can't do that yet because i don't have them, but i'll get this order in then when i receive them i'll put my multimeter on the psu to see what the current output is like. Thanks for your help.

I just got a reply from rapid I said "I wish to wire up two of these for a lamp. Do I need a driver or will a standard 12V Ac-Dc transformer suffice?"

and they replied saying "Thanks for your enquiry Matthew. A standard DC transformer will be enough to run these."

Guess that means I just need a transformer that is rated
input:230VAC 50Hz
output:12VDV 300mA or higher

also if i could find a laptop supply that was say 19VDC could that be used to create a 12V power supply somehow?

Just try to find a 12V DC power supply capable of supplying 1 A.  I am guessing that you will be able to such an artifact in a place that sells used junk.  In my country, the former United States, such places are called "thrift stores", where the word "thrift" implies that the things they're selling are priced low because it's just somebody's old junk that was given as a gift to the store. 

When new,  I have seen brick shaped 12V DC supplies powering things like portable hard drives.  Sometimes LCD monitors run from a 12VDC supply.   The portable-hard-drive example came to mind, because I've got a few of those.

Actually, looking at that catalog (RapidOnline) you linked to earlier, here is an example of the thing I am describing:
at a price of £8.97.

Just guessing that you could find a better deal for such a thing locally, or already existing in your junk box.

Yeah, funny you should mention thrift shops, cause when i have thought about it before i don't think there is an equivalent in the UK, the nearest thing would be charity shops that sell donated items but i know most do not accept electrical goods so lots of the things you see instructablers saying you can pick up at thrift stores you couldn't get for a charity shop. There are song hand shops but they are usually dealers buying and selling things so they wouldn't be as cheap as a thrift shop an often these shops solely sell vintage and antique 'second hand' items.

I imagine this would do the same job too at a slightly cheaper price:

I was hoping i might be able to find some old laptop supplies but these are usually 18-19V aren't they?

 I didn't see that one. That little 12V wall-wart looks like it would work too.

You know the electrical outlets in your country are strange looking.  Well... maybe the outlets in everyone's country are strange looking.

Regarding laptop chargers: Yes.  Most of the ones I have seen are 18 or 19 volts.  I might have seen a 16 V one once.  But, yeah, I think most of them are around 18 or 19V.

Cool, I'll just buy one of them. Not too expensive and it will save me time, i really need to get cracking with this.

Ok thanks, i may try contacting rapid again when i order as that datasheet is confusing.

Btw how did Yup and stave work out that the two bulbs will draw 300mA?

300 mA is approximately the number you get if you divide 3.8 watts by 12 volts. This is from the equation for power, P=I*V. Current is I = P/V.

should really have done that, being as i know all those equations from a-level physics :P that was gonna be my next step ;)

Hmm. I read the data sheet and made the opposite conclusion.



You can make something work with your own supply, and hopefully more credit from your DT teacher, if you use a couple of circuits like the one I've attached, total cost, less than quid a channel.

Set the resistor so that the current is 300mA.


LED driver.JPG

would I supply the input voltage from a standard AC/DC transformer then?

Use an old laptop supply, or buy a wall-wart from Rapid like this one:

Good point, I think I'll be able to acquire an old laptop supply easily enough.

which part number is it I want from these : http://www.rapidonline.com/Electronic-Components/LM317-Series-adjustable-voltage-regulators-29678/?sid=2b2a3088-02c7-4748-922e-12b125b95272

One of these per LED


looking at the datasheets- they say/ show in circuit diagrams 2 external resistors and some show protection diodes and some capacitors.

What will be necessary to achieve 12Voutput


I showed you the circuit you need. One resistor is all it needs.

Ok, take your word for it. Don't understand why the datasheet states two is necessary though,

Because you aren't making a VOLTAGE regulator, you're making a CURRENT regulator.