need diy led bulb curcuit please

[snake]

hi friends,i was planning to make some led bulbs for my home but i want to power them by 240vac.i want to connect the leds in parallel and to use either 3vdc of 12vdc but i think 12vdc is good.

i dont want to use any transformer for this application.does anyone have a bright idea of how can this be done.the circuit will be placed in the bulb housing itself.

thanks

[tanner0441]

Hi

I don't know if you are in the UK but I have some 240 V direct replacement for the 55W plug in spots, they were only about £2 or £3 each and they pull 3 W from the mains.  I have one over a stair well which is always dark and it is on 24Hrs.  

You can use capacitors as a way of reducing the mains to an alternative voltage, but I personally don't think it is worth the effort when off the shelf units are readily available.

You can also buy 12V replacement lamps.  Look on EBay I am sure you will find something.

Brian

[Opera House]

Old cell phone chargers are everywhere with quite efficient switchers in them capable of a half amp.  You can use caps in series, but most caps are junk with a lot of internal resistance. you should also use a resistor in series to protect the cap.  That limits just how much current you can get with a capacitor based system.  

[wooferhound]

I know you said that you don't want to use transformers, but that's how I do it . . .

http://www.fieldlines.com/story/2010/2/5/111750/6831

You might be able to experiment with this circuit and get it to put out 20ma to power your LEDs, but the light will flash at twice the line frequency . . .

http://www.fieldlines.com/images/scimages/231/pulsecrg.GIF

If you can get it down to some kind of DC voltage, you can calculate resister values using this page . . .

http://led.linear1.org/led.wiz

[snake]

hi,i am not in uk but i live in mauritius.but we use 240vac uk plugs here.has someone ever disassembled a 240vac led bulb.how is the circuit

[Bruce S]

Snake;

 To help you to understand and get further with this here's a good link to start reading up on.

http://www.fieldlines.com/story/2007/4/20/95351/1614

These are college level quality and will help you go from thought to implementation.

Cheers

Bruce S

[tanner0441]

Hi

I have never taken one to pieces but there are 20 LEDs on a disc about 1.5ins across and the whole lot is built into a direct replacement for the 55W halogen plug in spot light bulbs.

Brian

[Opera House]

One circuit I never see is boosting the supply voltage to the LED string in 12V applications.  A simple boost regulator circuit in constant current mode lets you put 5 or more LED in series with out wasting a lot of power in voltage drops and makes it easy to dim. When using 1W or 3W LED, being able to choose the exact number in a string is a big plus.