Power indicator LED for 50v+ supply

[CommanderLake]

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?

 

[Harald Kapp]

So Is there a solution that would use less power without taking much more board space?

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. ...

 

[CommanderLake]

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.

 

[Bluejets]

Run the LED at 5mA with a 10k resistor ....in most cases it would be sufficient brightness for an indicator.

 

[Alec_t]

You might even get away with 47k and 1mA if the LED is a modern high efficiency type.

 

[CommanderLake]

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.

 

[Harald Kapp]

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.