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Buying a dimmable power supply

Discussion in 'Power Electronics' started by firstoption, Jun 11, 2014.

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  1. firstoption

    firstoption

    9
    1
    Mar 8, 2014
    Good day to all,
    Please I Need your guide and support before buying this dimmable power supply:
    http://www.osram.com/osram_com/prod...ent-dimmable/optotronic-intelligent/index.jsp
    I have a PCB that has a cluster of 120 Leds on it with Series-Parallel connection.(A cluster is made of 5 Leds all connected in parallel).12 clusters(60 Leds)are then connected in series,this 12 cluster in series is now connected in parallel to another 12 clusters which is also in series.According to my calculation the PCB requires 200mA and 38.4V-43V( this is based on this series -parallel arrangement and the datasheet of the Led ):
    The Problem i am having is that the Dimmable Power Supply I finaly saw after so many search on the Internet has an Output Voltage range of 12V-54V and constant Output current of 250mA.
    My question is that,can i still use this power supply to power my PCB considering the fact that the power supply Output voltage range is up to 54V(more than the 43V that i need.)and at the same time it has a constant Output current of 250mA(although the absolute Maximum current Rating of the Led is 30mA according to the datasheet.-this will give me 300mA based on my Led Arrangement.)
    Your Support and guide will be highly appreciated in this Situation.
    Best regards.
    NOTE:I have only the Leds on the PCB,there are no other components.So the 43V and 200mA will be consumed only by the Leds.A copy of the Led datasheet is attached to this thread.
     

    Attached Files:

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Yes, I think it will be suitable, as long as the current isn't too high.

    The voltage you need (38.4~43V) is within the specification (25~54V). The output current is 25% higher than you want (250 mA vs. 200 mA) so you should check that LEDs can handle it.

    From your description of the it seems like the indivdiual LED current (assuming perfectly matched LEDs) is 1/10th of the applied current, i.e. 20 mA for the 200 mA total current you want. Running 250 mA will mean an average LED current of 25 mA. As long as the LEDs can handle this, you should be OK.

    LEDs are not normally connected in highly paralleled arrangements like this. LEDs in parallel do not current-share well; there is a natural tendency towards thermal runaway. This tendency may be increased at higher operating current.
     
  3. firstoption

    firstoption

    9
    1
    Mar 8, 2014
    Thank you Sir for taking the time to reply my question.i really appreciate your Kind gesture.With the explaination you gave above,it means i can power the PCB with the power supply.Actually the only fear i had before has to do with blowing up the PCB as a result of over voltage.Unfortunately the PCB was not made by me,it was made by somebody else.I was only asked to look for a constant current power supply that can be used to dim the Leds. I have equally informed the owner of the PCB,that the series-parallel Arrangement is not the best Option and that with time the Led may start developing faults.But it appears he cares less.So my only Task now is to get the Led working.Once again thank you for the Support.
    Best regards.
     
    KrisBlueNZ likes this.
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