I want to know for a constant led driver having voltage ranges of min-max, like 21-42VDC,150mA minimum and maximum how many LEDs can be connected in series.

Please help me regarding above matters.

  • 1
    \$\begingroup\$ That would depend on the LED operating voltage. Different color LEDs have different operating voltages. \$\endgroup\$
    – Justme
    Aug 13, 2020 at 6:48
  • \$\begingroup\$ How long is a piece of string? No LED data sheet means it's guesswork. \$\endgroup\$
    – Andy aka
    Aug 13, 2020 at 8:03

1 Answer 1


A single white LED tends to have a voltage drop of about 3 V. That means 'about' 7 to 14 single white LEDs. Without knowing how much tolerance your power supply has to load voltages slightly outside the stated limits, it would be safer to restrict that to 8 to 13 series single LEDs.

LEDs sometimes come packaged in multiple series units, so would have a much higher terminal voltage. Connect the LEDs you want to drive to the supply (making sure they are specified to handle the 150 mA) and measure the voltage.


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