Author Topic: Idea needed: Led indicator for wide voltage ranges.  (Read 1006 times)

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Offline Khakimov

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Idea needed: Led indicator for wide voltage ranges.
« on: March 11, 2019, 09:55:13 pm »
Given: A lot of fuses that protects some power electronics (transformers, incandescent lamps, relays). Sometimes a fuse blows and it needs to be spotted and replaced. But it is very hard to carefully look through a lots of fuses and inspect each thin melting wire. So I need some indication device of a blown fuse that connects to fuse itself.

This indication device needs to be:
1. Simple
2. Small
3. Working on AC/DC 12..220V ranges.

My first thought was "Hey, let's just choose a proper resistor!":

But in order to LED be nearly visible on 12V in case of 220V resistor will dissipate a lot of heat, so it needs to be huge.

Well... let's add power-limiting capacitor!:

But in this case indicator looses an ability to work on DC voltages.

Now I am thinking of using resistor + blinking leds with ICs inside them to reduce current consumption and thus a power dissipation on resistor. Most of blinking leds have a 50% duty cycle and there is not much of power saving. I am trying to find SMD blinking led with duty cycle of about 10% (100 msec on, 1 sec off) but still no success with that.

1. Any advices of how to find leds with small duty cycle will be appreciated (maybe they are not existing at all?).
2. Perhaps I am missing another ways to make simple blown-fuse indication...

Thanks =)
« Last Edit: March 11, 2019, 10:08:49 pm by Khakimov »

Online Benta

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Re: Idea needed: Led indicator for wide voltage ranges.
« Reply #1 on: March 11, 2019, 10:00:30 pm »
For 100...230 VAC, the simplest is a neon lamp + resistor. Small, simple, inexpensive.

Offline Zero999

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Re: Idea needed: Led indicator for wide voltage ranges.
« Reply #2 on: March 12, 2019, 09:59:12 am »
I think he wants something which will work over a wide voltage range.

A flashing LED won't work at such a high voltage because when it goes off, it will be exposed to the full voltage. It's theoretically possible to design a transistor constant current source which will draw say 1mA, over a very wide voltage range, but it's not compact.

The attached circuit has a negative temperature coefficient. The series pairs of D2 & D3 and D4 & D5 can each be replaced with a 6.2V zener diode and R1 and R2 increased to 10k, for better temperature stability, but the minimum operating voltage will increase to over 12V.

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