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Using an LED with 220V AC

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haxan

New Member
Hi, can anyone suggest a simple circuit which lights up an LED with 220V AC. I am trying to make something without the use of transformers.

Maybe a bridge rectifier and a resistance connected with LED.
What should be the resistance value (is 1M enough) ?
 
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SYE

Member
Most LED's don't like being reversed biased by more than a few volts so you will need to add some diodes to protect your LED.
 

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cobra1

New Member
ok lets see

220 v AC rectified will give you about 300v DC

since you didnt put the specs of your led lets assume your led is red..2.4v @ 20ma

this works out that you need a resistor rated at 15k ohm @ 6watts

Thats a big resistor, it will just gets hot and use far more power than the led uses.
Simply put its impractical.

What do you intend using this for as there is more than likely a better way to do this
 

haxan

New Member
I want to attach an LED in a switch board which should glow when electricity is coming in that board and should not glow when not.

I actually made a circuit earlier for a Fan dimmer which had 220V AC come in, connected to a bridge and went directly into NPN-Optocoupler for Zero crossing detection. which gave pulses to microcontroller when ever a zero - crossing went by. For this reason i thought that it would be easy to do this.

Also a few years ago i saw a small night light made from one LED (green) which plugged directly into 220V Mains. It didnt have any transformer.
 

Kryten

New Member
You culd also put diodes in oposites directions without rectifiing ( you know they will turn off and on @ 50Hz) ;)
 

yash gupta

New Member
I found a similar thread http://www.electro-tech-online.com/threads/convert-220-ac-to-3-6-vdc-for-lighting-led.36652/ however they are using Capacitors as well which will make circuit bulkier.

Will this circuit work too ?
It is the only solution that i know. you will have to use a circuit as shown by the above post.
The impendence of the cap is used here instead of a resistor to limit the current.
The benefit is that a cap doesn't heat up, as the current ans voltage are 90deg out of phase.
You can use a simple formula for the impendence of a cap.
Z=1/(2*pi*50*C)
Generally, as it is shown, 180-220 nF is fine for a 5mm red led.
And dont forget to use a diode to prevent high reverse voltages.
A 1n4007 in opposite dir in parallel to the LED will do.
Make sure that the voltage rating of the cap is 400V or so.

But, this type of supply is not recommended if you plan to use it for serious circuits.
Use a limiting cap,a fuse,a full wave bridge rectifier, a zener and a filter electrolytic cap to create a useful power supply without transformer.
Limiting caps with values ranging upto 2.2uf 400v are small enough to be used as a cheaper and smaller alternative to transformers.

But, don't think of using transformerless supply for expensive circuits. They can blow anytime.
 

yash gupta

New Member
Sorry for late reply.
That 1k is not really required.
Use 4007 instead of 4148 and 380nf or near about.
 

colin55

Well-Known Member
Use 4007 instead of 4148 and 380nf or near about
The circuit is halfwave and you will get 25Hz flicker, which is noticeable. 100n caps will only deliver 10mA in full wave or 5mA in your situation, so a few 100n in parallel is required. They need to X2 caps or at least 400v.
You really need a full wave rectifier at the front end for better results.
 
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