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Topic: led advice (Read 1 time) previous topic - next topic

IGraham

Hi
a few simple questions - if you know the answers simple

I've got three 3v 3w led's do i wire them in series or parallel - think its series but not certain

Led driver, is there something special about the powering device being a dedicated 'Led driver' or will any powering device do, such as this   240v to 9v .Or is this one  a better option

Or could someone suggest a more suitable powering device
 

Paul__B

I've got three 3v 3w led's do i wire them in series or parallel - think its series but not certain
Always series.

Led driver, is there something special about the powering device being a dedicated 'Led driver'.
Yes, you need one for driving LEDs.  Search for a 10W LED driver.   Look for a 10 W driver supplying 750 mA as specified on the web-page you cite.

or will any powering device do, such as this   240v to 9v .Or is this one  a better option
No, they are not LED drivers.

IGraham

Thanks for the reply
the info is appreciated

Paul__B

So, a LED driver is always a constant-current supply, so you put all your LEDs in series so that all carry the same current.  It must be capable of supplying somewhat more than the nominal voltage of the series string, but it must limit the current to that specified.

The datasheet you indicated, for white or ultraviolet LEDs (which are the same technology) shows a requirement for 750 mA, at which current three in series will drop approximately 12V (4 V each, plus or minus 0.5 V) or up to perhaps 14 V.  That is then, the specification you require for your constant-current LED driver/ power converter.  You coudl never know what the correct voltage was due to variation in LED characteristics, including temperature.

If you then want to add chains in parallel, you must provide a separate current controller for each.


Chagrin

http://www.ebay.co.uk/itm/DC-800ma-Constant-Current-LED-Drive-Driver-Power-Supply-12V-Car-battery-10W-C50-/221771855009?pt=LH_DefaultDomain_3&var=&hash=item33a2a1f4a1

This is based on the PT4115 chip for which you can easily find the datasheet. If you can manage to lift pin #8 on the chip and solder a wire to it you can use that pin for PWM dimming. The current of the module is set by R1 and R2; they are in parallel so that's (.2 x .3) / (.2 + .3) = .12, and then per the PT4115 datasheet the current is .1 / R, or .1 / .12 = .833A (.833ma)

Be aware that the above module and many others like it employ a bridge rectifier, the four diodes labelled "SS14", to make them safe for both AC and DC current (less than 30V). In a battery powered environment that rectifier will waste a little power and you might want to remove it to prevent that.


IGraham

for some reason didn't get notifications for the last two replys

thanks for the extra info, brain cells are protecting slightly but i shall digest

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