# AC 230V LED driver design help



## pavithra_uk (Nov 7, 2011)

I need to drive 1~3 LEDs around 500 ~ 700 mA current from AC 230V line.

I know there are many controller ics available. but I need driver to design without any IC.

anyone know a circuit that use FET or other transisters only ??

there is a method that use capacitor current limit. but for 500mA it require big cap and then its not a practical.


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## jason 77 (Nov 7, 2011)

Simplest way would be to use a wall wart, or something along the lines of a Meanwell power supply that supplies the proper current and voltage.


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## xul (Nov 7, 2011)

Proved surprisingly difficult, needed a spreadsheet and cut-and-try 'cause I'm too lazy to do the higher math necessary.

Using 3.5 v for an LED voltage

31 >enter V
40 >enter series R
0.6875 1 LED current
0.5125 3 LED current

31 vdc in series with a 40 ohm resistor meets your specs.

A few 230vac, 1Adc plug in wall transformers with their outputs in series plus a power resistor should do it.

In the US, 2 ea. of these from Hosfelt.com would work, both outputs and inputs in series.


*18 VDC @ 1 AMP*
*$​



4.95*​












56-891​












​




*Mfg. - BIO MEDICAL
Mfg.# - WD1H1000LCX
3-5/8" x 2-1/2" x 2-1/8"
Input: 120 VAC, 60 Hz, 20W
Output: 18 VDC @ 1 Amp
The enclosure and 6 ft cord are black.
Center is positive for polarity. Coaxial
Jack: OD - .215", ID .098"*​




The new resistor value would then be

36 >enter V
48 >enter series R
0.677083333 1 LED current
0.53125 3 LED current

or slightly higher.


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## pavithra_uk (Nov 7, 2011)

Thanks for replies.

using transformer, its too bulky. anyone know way to design step down converter ? (non isolated)


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## AnAppleSnail (Nov 7, 2011)

pavithra_uk said:


> I need to drive 1~3 LEDs around 500 ~ 700 mA current from AC 230V line.
> 
> I know there are many controller ics available. but I need driver to design without any IC.
> 
> ...



Sometimes people come here and ask how to do something and my first reaction is 'Why do you want to do that?' Sometimes the thing you're asking about is like this:

"Hey CarForums, I need to build a periscope for my car. No, really. I can't see around the hood to drive while it's open!"

In that case, the problem isn't seeing around the hood, or how to build a periscope. So I must ask:

Why can't you use any IC chips? Can you use diodes? Are you limited in parts you can buy? How good are you at soldering and electrical safety?

In theory you could make a rectifier bridge with 4 diodes, then use a resistor and have a low-power-factor light that flashes on/off at twice the Hz of the AC power. Is that good enough? Remember that 230V is the average, the maximum is higher. Then you can pick a resistor and check with a multimeter to adjust to the right current. Oh, don't DIY a rectifier bridge unless you know what you're doing. Playing with line voltage is bad juju.


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## pavithra_uk (Nov 8, 2011)

AnAppleSnail said:


> Sometimes people come here and ask how to do something and my first reaction is 'Why do you want to do that?' Sometimes the thing you're asking about is like this:
> 
> "Hey CarForums, I need to build a periscope for my car. No, really. I can't see around the hood to drive while it's open!"
> 
> ...



Why I asked such question : Limited parts. Its very dificult to buy these ics from here Sri Lanka. So I have to use commonly available parts. unfortunately, available DC-DC converters doesn't meet High voltage requirements.


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## xul (Nov 8, 2011)

pavithra_uk said:


> Thanks for replies.
> 
> using transformer, its too bulky. anyone know way to design step down converter ? (non isolated)


Your problem may be overconstrained. Time to relax one or more design goals.


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## jtr1962 (Nov 8, 2011)

My suggestion is to use 20 mA surface mount LEDs instead of power LEDs. You'll get better light distribution, and it greatly simplifies your driving requirements. In this case you might use anywhere from 25 to 75 20 mA LEDs in series to obtain the same light as 1 to 3 power LEDs driven at 500 mA to 700 mA. Because the current requirement is less, you can use a smaller capacitor in a capacitor-fed full-wave bridge. The capacitor-fed FWB is about the simplest way to drive LEDs off AC.


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