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How does a voltage divider circuit to run an LED?

Posted: Mon Jun 07, 2021 2:34 am
by Markkim
Hi, all
Recently, I have a system running at 62V max, 54V nominal based on voltage divider formula (formula source https://www.apogeeweb.net/electron/what ... -rule.html). I wanted to have a little alert LED, so I was thinking about using 10, 1kohm resistors, and adding the LED bewteen the 9th and 10th (or 1st and 2nd, if it matters), to get at most 6V and just a few mA.

Is a better/easier way? Is this a really crappy way? Or is this a perfectly fine way?

Re: How does a voltage divider circuit to run an LED?

Posted: Mon Jun 07, 2021 3:19 am
by dyarker
A "regular" indicator LED is commonly 20mA maximum. Design for about 17mA.
The forward drop of an LED depends on color. 1.8V for red, to 3.8V blue, other colors in between.

Suggest you calculate 62V for 19mA through LED. That leaves a margin for a little over 62V, and 54V long term safe. If that it too bright, lower current is okay. (below 5mA LED may not light)

Cheers,

Re: How does a voltage divider circuit to run an LED?

Posted: Mon Jun 07, 2021 2:10 pm
by dacflyer
Perhaps this might help you ???
http://ledcalc.com/

Re: How does a voltage divider circuit to run an LED?

Posted: Wed Jun 16, 2021 6:36 pm
by haklesup
its a perfectly reasonable way but does not provide as much safety factor as it would if you put a regulator in between. For example if the LED fails and goes open circuit, the full voltage will be across its terminals. 62VDC is safe but 62VAC might give a little zap

if it were under 40V I would suggest one of the many off the shelf DC-DC buck boost regulator modules in CC mode but for your range and a simple application, the divider should work

Re: How does a voltage divider circuit to run an LED?

Posted: Thu Jun 17, 2021 12:23 am
by dyarker
If he was using 62VAC, the LED would be destroyed immediately unless also including a standard rectifier diode in series.

Re: How does a voltage divider circuit to run an LED?

Posted: Fri Jun 18, 2021 12:05 am
by Markkim
Thank you for sharing ideas..
I have a bunch of 1k, 1/4W resistors, so 10 of those will work fine. I guess that 6mA at 60V is only 360mW, which might be a bit high. I could always use a lot more resistors and experiment by reducing it until I get to a suitable brightness.

Re: How does a voltage divider circuit to run an LED?

Posted: Fri Jun 18, 2021 1:14 am
by dyarker
Five 1K resistors in series with the LED should work.
The wattage will be divided across the 1/4W resistors, so will be less than 1/4W on each.
If not bright enough, go to four resistors.
Will need color of LED for closer calculations.

Cheers,

(late add - be careful of polarity of LED. If you put it backwards it will be destroyed. PIV is typically 5V, your supply is 10+ times that!)