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230v AC powerd LED

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fever said:
hi all
i want to power a single bright LED(3v @20ma) using 230v mains.
i found below ckt for this purpose,
http://users.pandora.be/ranzigen/td_circuits/circuits/net_knipper_led/net_knipper_led.html

but iam unable to find the diac(BR100) used in this ckt.so is there any replacement for this BR100.
pls help me
thanks

Hello,
You don't need a DIAC.
Try to use only a 1N4007 Diode, the LED and a 11k 5 Watts or 12k 5 Watts resistor.

AC "live" - 1N4007 - 12k 3W Resistor - LED - Neutral (GND).
 
Ballast resistors and such are REALLY inefficient and make an awful lot of heat. 20mA LED makes 4.5W of heat in the resistor and @3v only gets 0.060W itself. I guess it's not too bad for 1 low power LED.

Best thing is a driver like the HV9910, which makes a current mode buck converter which is extremely efficient. Some other Supertex parts have power factor correction. Look up **broken link removed**
 
well iam looking for a ckt which is as simple as possible.
efficiency is not necessary,but heat generation could be a problem,where iam going to place it.
so insted of supertex chip(not available in my area,and even can't order online) is there any other ckts for this purpose...
 
ok.
its for glass based wall hanging,in which i want to fix a bright(not ultra bright) LED.the place is so small.so i can't use transformer..
any advice..
 
Why 220VAC?

In either way you need a cable to the LED, so the cable can't be a problem right. If you don't have space for electronics, just put the LED on the wall and put some (hughe) electronics elsewhere and bring the cable to the LED. That way no 220Vac, no heat around the LED only 20mA :)
 
mcs51mc said:
In either way you need a cable to the LED, so the cable can't be a problem right. If you don't have space for electronics, just put the LED on the wall and put some (hughe) electronics elsewhere and bring the cable to the LED. That way no 220Vac, no heat around the LED only 20mA :)

EXACTLY - once we know the specific reason, it soon becomes clear it's not a sensible solution to feed it from 220V. As mcs51mc says, feed low voltage to the LED, and have the mains transformer elsewhere - probably as a wallwart?.
 
You can use a capacitor instead of resistor to drop the voltage. There is no power dissipation there.

Below is a schemtic that illustrates it. I used two LED's to remove the DC in the capacitor. The 1K resistor is there to limit any surge current when you turn ON the switch. Most of the voltage drop will be in the capacitor.
 

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motion said:
I used two LED's to remove the DC in the capacitor.

Bear in mind, that if you are only using one LED, the other LED in the diagram will have to be replaced by a regular power diode (1N4004 or similar).
 
Or use a bridge rectifier and you either can halve the size of the capcitor or double the brightness of the LED.
 
thanks guys.
i'll try above schematic.but what shld be the rating(wattage) of 1K resistor? and cap is 225,400v.is it 225uf 400v?
please clarify
 
steev said:
thanks guys.
i'll try above schematic.but what shld be the rating(wattage) of 1K resistor? and cap is 225,400v.is it 225uf 400v?
please clarify

If you have to ask you SERIOUSLY! shouldn't be attempting to build it!. You are aware that this will make your entire circuit live to the mains?, including the LED itself!.

The circuit shows the capacitor as a 225uF electrolytic - which looks completely (and dangerously!) wrong - a 1/1000th of that, and non-electrolytic, would be more like it?. Not that I'm suggesting that would be the correct value!.

Seriously, use a wallwart, and feed low voltage to the LED, don't run it off live mains!.
 
I agree with Nigel Goodwin, nubes souldn't mess around with high-voltage high-current sources like the mains, buy a cheap and nasty DC adaptor and power you LED from that, note you'll also need a resistor or the correct value.
 
fever said:
ok.
its for glass based wall hanging,in which i want to fix a bright(not ultra bright) LED.the place is so small.so i can't use transformer..
any advice..

For the sake of your own safety and others , use a small battery please!
 
A 225uF capacitor will make a very loud BANG in that circuit.
No, the resistor would smoke badly just before the LED burned out.
 
motion said:
FYI, 225 is a 2.2uF capacitor. It has to a high voltage capacitor though.

I know how to read capacitors thank you, but you DON'T label it like that on a circuit diagram! - some small capacitors are marked using that method (but it would be unusual to find a 2.2uF so marked?). Your diagram clearly marked the capacitor as 225uF, and even showed it as an electrolytic! - if you're commonly labelling your diagrams like that you're going to cause massive confusion!.
 
I use a lot of LED indicators on 230 Volts AC.
If you use a high efficiency LED you only need to run it at 3 or 4 mA.

I usually use 2 * 33 or 39 k Ohms 1 Watt in series, a 1N4007 in series and LED ( any colour ) with a 1N914 or eq antiparrallel with LED.

{Phase} {39k Ohms} {1N4007} {LED and 1N914} {39 kOhms} { Neutral}

The power drawn is less than 1 Watt and the resistors hardly warm up.

Put enough sleeving around the mains wiring and it will work very reliable.
 
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