Printer power supply for 20W SMD LED chip?

Thread Starter


Joined Jul 10, 2016
I got this printer power supply with 2 out puts, 32v @750mA and 16v @200mA. Can I use it to power a 20w smd led rated 30-32V @560-600mA and a 100 ohm 1/4w resistor on the 16v for cooling fan 12v @150mA or if i need a head sink and a cooling fan for the led?


Joined Apr 4, 2016
The LED will need to be current controlled. The LED voltage is only approximate. Normally this is done with a special switch-mode controller that regulates the current.

The current could be controlled with a series resistor but to get accurate control the power supply voltage needs to be 10-20% higher than the expected LED voltage and there will be quite a lot of power lost in the resistor.

So I don't think your power supply is any good for this.


Joined Jun 22, 2012
Don't see why not, you need a constant current source for the led,like a lm338 or your using a series resistor.
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Joined Sep 17, 2013
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Joined Jul 11, 2016
16v @200mA , 100 ohm 1/4w resistor , fan 12v @150mA
the fan at startup can draw some 3 times the nominal power - which may develope the supply fault over a longer period of time ? half a year or more - which also may not dev. that fault if the supply design is such - the momentary 70% overload falls into standard 2x nominal short circuit curent range - the bad thing here is when switched power supply starts and also the fan starts - so if your fan starts normally - no problem - if if not - time the fan start by some 3 to 10 seconds - if it still gets slow into speed - it's no good

((( despite the fan starting normally the near spec continuous or longer duration loading may heat up the supply itself - the hotter the semiconductor the shorter it's aging . . . )))