# Need Help

Discussion in 'General Electronics Discussion' started by Soundzman, Mar 27, 2013.

1. ### Soundzman

11
0
Feb 21, 2013
I am designing a small led panel .

I used the led calculator to design the circuit for me .

r = 1 ohm

But the led's burns out in few seconds .

I'm using normal led's and 12v( 3 amps ) as source .

Last edited: Mar 27, 2013
2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
Beware calculated values with very small resistances like this.

Repeat the process, except this time specify only 2 LEDs in each string.

3. ### Soundzman

11
0
Feb 21, 2013
Can you explain as in what i can do to make it work .

Thanks a lot Steve

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
What colour LEDs are these (I presume they're white) and what current do you want to run them at? (I assume 20mA)

You have 4 strings of 3 LEDs. What you need is 6 strings of 2 LEDs.

The resistor for each string of LEDs is about (12 - 2*3.5)/0.02 = 5/0.02 = 250 ohms. Use a 270 ohm resistor.

5. ### Soundzman

11
0
Feb 21, 2013
I 'm sorry , i new to all these things .

I'm using Red Led for testing ( The board has all three colours connected as a different arrays ) .

The storekeeper where i got the LEd from said , its 3 volts and 200 mA each.

So ill try , 2 led and 270 ohm in series and 6 strings .

Thanks steve . i'll try and get back to you .

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
You'll need to show us a picture.

Different colours have different forward voltages and will require different resistors.

If they are really 200mA, then these are high power LEDs and are best used with a current source (now it's getting complicated)

For more information go to the tutorials section (on the bar at the top ^^^) and look for the one that answers LED questions.

7. ### Soundzman

11
0
Feb 21, 2013
Thanks a lot Steve . I'll sure check out and make it work....

8. ### gorgon

603
24
Jun 6, 2011
If the LEDs are 3V you may use 3 in series as in your drawing, but you need at least 15 ohms in series for the 200mA limit. Personally I would start with 150 ohm and look how bright they are with 20mA. You should be aware that red LEDs only drop around 1.7V, and this explains the burnout.

9. ### Soundzman

11
0
Feb 21, 2013
Thank you so much for the reply .

Will this work for RED . Will i get maximum brightness with the following

R = 10 ohm

What about green ? what is the voltage drop ?

10. ### gorgon

603
24
Jun 6, 2011
All depends on the LEDs you use. You need to look into the data
sheet for the different parameters.
Absolute max pulsed current is not the same as nominal continuous current, so the datasheet is the answer.

This just an estimate:
If you use normal small red LEDs with this circuit, you'll burn them out. Use R=100 ohm, this should give you a safe current at 12V.

11. ### Raven Luni

798
10
Oct 15, 2011
Your calculator is crap. No other way to say it.

12. ### gorgon

603
24
Jun 6, 2011
I think mine is working ok?

Last edited: Apr 6, 2013