Will this led light circuit work?

[ben7]

I am wondering if this led light circuit will work. It would run off of 120volts AC and it has 20 white leds. Since this would work off of the line voltage I want to see if anybody else thinks it is incorrect or dangerous.

 

[HarveyH42]

I have a problem with Word documents, they want me to buy... Without even looking, yeah, it's probably dangerous if you have to ask...

 

[ben7]

The leds are fed through a rectifier in series with a .68uF capacitor connected to 120 volts. I found the same circuit on the internet except it runs off of 230 volts, www.circuitstoday.com/wp-content/uploads/2009/03/mains-operated-led-lamp.jpg

 

[Diver300]

The circuit should work. You should really have a resistor of 100 ohms or so in series with the 0.68 uF capacitor, to reduce the inrush surge as you turn on.

Transformerless circuits like that can be dangerous to fault find.

I can't really see why you don't have a smaller C1 and put all the LEDs in series. You then don't need R2 or R3. C1, combined with the mains frequency and voltage are what control the current. R2 and R3 are only needed to distribute that current evenly in the two strings of LEDs. You've got lots of voltage so 20 LEDs in series is still far less than the supply, so there is no reason not to do that.

Edit:- R2/R3 will keep the current more constant. However, with C2 there, the current won't drop to zero for a long time so the LEDs won't appear to flash.

 

[Diver300]

The leds are fed through a rectifier in series with a .68uF capacitor connected to 120 volts. I found the same circuit on the internet except it runs off of 230 volts, www.circuitstoday.com/wp-content/uploads/2009/03/mains-operated-led-lamp.jpg

That circuit is not good. Not only the lack of series resistance, but there is nothing to keep the current the same in each of the 6 strings of LEDs.

 

[ben7]

I tested the circuit, only running a few leds, I hate that 60hz flicker from the leds from half of the ac waveform, even those compact florescent lightbulbs-the twisty ones-make me get headaches...The other problem is if you try to make a direct incandescent replacement, you would have limited space, so you would have a limited amount of leds.

 

[ben7]

I think I will get away with a .22uf capacitor. It seems like it will work. I currently have it isolated using two transformers back to back. The two transformers put out isolated 120volts AC, the circuit still does it's job well, putting out about 60volts DC! When I drew 40mA from it, the voltage barely dropped with a .22uF capacitor. I need to buy the parts and wait a week for them to arrive. I will try to find the time to put up pictures too!

 

[ben7]

That circuit is not good. Not only the lack of series resistance, but there is nothing to keep the current the same in each of the 6 strings of LEDs.

I agree too! just shows never to trust stuff you find on the internet!

 

[Diver300]

the circuit still does it's job well, putting out about 60volts DC! When I drew 40mA from it, the voltage barely dropped

There's something wrong there. The supply is 120V AC, so the peak voltage is about 170 V. Most of the voltage should be dropped across C1, so the current should be fairly constant. That means that the voltage should change a lot if you change the current drawn.

However, LEDs have a fairly constant voltage drop, so putting more strings of LEDs in parallel won't change the voltage or current much, it will just distribute the current that is controlled by C1 to more strings of LEDs.