Printer power supply for 20W SMD LED chip?

Discussion in 'Power Electronics' started by Davoinn, Aug 7, 2016.

  1. Davoinn

    Thread Starter New Member

    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?
  2. Marley


    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.
  3. Suman Kundu

    New Member

    Aug 7, 2016
    Please help me to find the portion whewhere I can write my problem
  4. Dodgydave

    Distinguished Member

    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.
    Last edited: Aug 8, 2016
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Click the 'Forums' tab near the top of the page,
    Click on the appropriate forum title,
    Click the 'Post new thread' button near the top right of the page.
  6. Davoinn

    Thread Starter New Member

    Jul 10, 2016
    thanks for the reply's
  7. ci139


    Jul 11, 2016
    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 . . . )))