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Power indicator LED for 50v+ supply

Discussion in 'LEDs and Optoelectronics' started by CommanderLake, Aug 12, 2019.

  1. CommanderLake

    CommanderLake

    178
    5
    Oct 2, 2012
    I would like to have an indicator LED for the output of a boost converter but a simple resistor>LED would consume about 500mW and require a relatively large 1W resistor and I really don't want to use so much power just to see that the output is live.
    So Is there a solution that would use less power without taking much more board space?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,137
    1,846
    Nov 17, 2011
    Quite a few, I say.

    1. Use the low input voltage of the converter to drive the LED. Sense the output voltage using a comparator and turn on the LED if the output voltage is o.k. (example).
    2. Use a 555 timer chip to pulse the LED if the output voltage is o.k. Pulsing will reduce the average current.
    3. Use a 555 timer as above (#2) but use an output inductor in series with the LED to create a kind of primitive step-down converter.
    4. ...
     
  3. CommanderLake

    CommanderLake

    178
    5
    Oct 2, 2012
    I already considered a BJT and suitable resistors but board space... its only an indicator LED, I dont want a relatively large 555 circuit.

    Keeping in mind I have to be able to solder the components with a standard soldering iron.
     
  4. Bluejets

    Bluejets

    3,444
    698
    Oct 5, 2014
    Run the LED at 5mA with a 10k resistor ....in most cases it would be sufficient brightness for an indicator.
     
  5. Alec_t

    Alec_t

    2,630
    693
    Jul 7, 2015
    You might even get away with 47k and 1mA if the LED is a modern high efficiency type.
     
  6. CommanderLake

    CommanderLake

    178
    5
    Oct 2, 2012
    I've selected this LED but its the brightness for a given current I'm not sure about, I think I will go with 10k on the output as Bluejets suggested and 2.2k on the input, I just need the output LED as a warning that its armed and dangerous.
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    9,137
    1,846
    Nov 17, 2011
    Acc. to the datasheet the LED will light up with as little as 1 mA. Simply test whether the intensity is good enough for you.
    upload_2019-8-13_18-54-45.png
     
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