2 LED in a series circuit troubleshooting

[nintendude49]

On a project of mine, I'd like to have 2 LEDs in a series as opposed to parallel because it uses considerables less wattage ....
But the source voltage is 3.0, and the forward volt on the LEDs is 1.7, and it seems when in a series, the forward voltages add up together, so i need an at least 3.4 volt source...

any ideas....?

Thanks,
-T

 

[rjvh]

you're right

what is the aplication??

Robert-Jan

 

[RODALCO]

Perhaps build a 3 volts joule thief.

 

[davidbball13]

joule theif is amazing it connected a 9 volt batter to it and the led still it and the read out on my Meters was 10 volts. and with out the joule theif the LED blew out. amazing. and you can run them off the really small watch batterys

 

[Hero999]

Look at the schematic, it's not surprising it blew the LED. If you connect a supply voltage higher than the LED's forward voltage, then you're effectively connecting the LED across the battery with no series resistor!
**broken link removed**

Building a 3V Joule Thief to power two 1.7V LEDs shouldn't be a problem as 3V<3.4, just check that the forward current doesn't exceed the maximum rating.

 

[nintendude49]

thanks for the replies,

right now im workin on modding my wii remote. like for this one, i'm adding LEDs above two hole spots in the back:
**broken link removed**
such that the holes light up when the controller rumbles.

a joule thief? I've never heard of em. But would I retain the effientcy using a joule thief/ 2 LEDs in series as opposed to just 2 LEDs in parallel.

thats my only concern, because, at least according to my calculations, a series circuit would use 1/4 the wattage the parallel circuit would.

thanks,
-T
**broken link removed** **broken link removed**

 

[shaneshane1]

thats my only concern, because, at least according to my calculations, a series circuit would use 1/4 the wattage the parallel circuit would.

They will use the same amount of Watts!

the parallel circuit will waist most of its power at the resistor and maybe around Eg:40mW at the LED if you use 1 resistor per LED then you will waist twice as much power!, you could use 1 resistor with 2 LED's in parallel but there is no way of knowing how long it will last.

and the series circuit will spread it out over the LED's
Eg:40mW at each LED

So if you measure the watts from series and parallel they will add to be the same, its just that with the series circuit you get to light another LED for free

 

[Hero999]

Connect the LEDs in series.

For a start paralleling LEDs without separate series resistors is a bad idea as they're likely to have slightly different forward voltages and one will hardly light and the other will blow up.

Secondly, even if you could parallel the LEDs, doing so would resuld in a forawd voltage of 1.7V which is too low for a Joule Thief running from 3V. Remember the input voltage must always be lower than the output voltage, as I explained in my previous post.