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Replacing Neon Lamp with LED

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paul_g_787:
I have a device here that I wish to replace the failed Neon power indicator.

It has no low voltage DC as it is a mains appliance, so it needs to run from the mains voltage.

I have done a lot of research and learned about capacitive drop supplies.  I have dismantled and reverse engineered a few LED light bulbs and learned the equations for capacitive reactance.

I have finally settled on this design which supplies the LED with 2V 10mA from the 240V AC Mains.
It works brilliantly and the LED should last a long time on 10mA.

Is there any improvement that can be made to this design?

My main concern about putting a fuse on it, as it is directly across the mains. Could I perhaps move R2 to the other side of C1 and change it to a fusible resistor? How would I calculate which fusible resistor?

mikeselectricstuff:
The 100uf cap is overkill.
Do you need as much as 10mA?
For a power indicator, a low-current LED and series resistor  for 1-2mA could be fine. Use a fusible reistor for R2. Fusible resistors don't have a current rating, they are just specced to not catch fire if they pop.

paul_g_787:

--- Quote from: mikeselectricstuff on October 18, 2021, 05:17:18 pm ---The 100uf cap is overkill.
Do you need as much as 10mA?
For a power indicator, a low-current LED and series resistor  for 1-2mA could be fine. Use a fusible reistor for R2. Fusible resistors don't have a current rating, they are just specced to not catch fire if they pop.

--- End quote ---

100µF is just one I had lying around. I also have 10µF would that suffice for C2?

The LED is a standard 20mA 2V LED. Running it at 20mA was a bit too bright but I found at 10mA it looks about right in a dark room.

If I replaced R2 for a fusible resistor would it be better to put it before C1?
And how would I spec the correct wattage of fusible resistor?

I notice in the regular LED light bulbs they just use 0.25W fusible metal film resistors, but they are before the dropper capacitor.

tunk:
You could also take a look at this: https://youtu.be/Q23uh7AjjXw

paul_g_787:

--- Quote from: tunk on October 18, 2021, 05:36:30 pm ---You could also take a look at this: https://youtu.be/Q23uh7AjjXw

--- End quote ---

Yes I did see Big Clive's video already :) That is where I got some of my information from.

I decided to add the smoothing capacitor as the flickering (although minor) was annoying and noticeable in the dark.
And I came across the idea for the Zener Diode just to help protect the circuit from High Voltage spikes on the mains.

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