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Led circuit

davlin

Hi sorry this is probably really basic stuff for you guys I have 3d printed a design and want to light it with some 3mm leds I have seen with a forward voltage of 3.3v , forward current 30MA , reverse voltage 5v, would like to use 24 of these but do not know how to carry this out power source , resistors needed , series or parrellel wiring ect ect

Please could someone help.

Regards David

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  • David,

     

    There's lots of ways to drive the LEDs and it depends on what type of supply voltage you have available. It also depends on the LED specs. The specs you gave look like perhaps Absolute Maximum Ratings and not the specs we need for design. In particular, the forward voltage and current seem a bit high perhaps, but it all depends on the type of LED you've picked and I didn't see a part number nor a manufacturer.

     

    Let's assume you're using 24 VDC for power. Make sure to get the polarity right or you could damage some or all of your LEDs. My cals are based on the specs you provided since I have nothing else to go by.

    --You can use 3 parallel strings of 8 series LEDs with no series resistor, or:

    --You can use 4 parallel strings of 6 series LEDs with a 140 ohm, 1/4W series resistor in each string, or,

    --You can use 6 parallel strings of 4 series LEDs with a 360 ohm, 1/2W series resistor in each string.

Reply

  • David,

     

    There's lots of ways to drive the LEDs and it depends on what type of supply voltage you have available. It also depends on the LED specs. The specs you gave look like perhaps Absolute Maximum Ratings and not the specs we need for design. In particular, the forward voltage and current seem a bit high perhaps, but it all depends on the type of LED you've picked and I didn't see a part number nor a manufacturer.

     

    Let's assume you're using 24 VDC for power. Make sure to get the polarity right or you could damage some or all of your LEDs. My cals are based on the specs you provided since I have nothing else to go by.

    --You can use 3 parallel strings of 8 series LEDs with no series resistor, or:

    --You can use 4 parallel strings of 6 series LEDs with a 140 ohm, 1/4W series resistor in each string, or,

    --You can use 6 parallel strings of 4 series LEDs with a 360 ohm, 1/2W series resistor in each string.

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  • in reply to kkazem

    Lets not forget the most efficient way to drive LED;s, constant current

     

    typical LEDs (Per LED) will require about 20mA.

     

    Bigger powered LED COBs etc are arrays of LEDs and the overall current will depend on their configuration and typically the LEDs inside the unit are very closely matched. There still constant current devices for best performance.