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..
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
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.
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.
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..
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!.