How to power LEDs

I have been trying to power about 20 LED's but I have not had any success so far.

When ever I connect the LED's there would be a really large drop in brightness and sometimes when I connect them in parallel, some come on and others stay OFF, and some blow up. I would like to have an idea on how to power the LEDs.

Thanks!

I suggest you connect 4 rows of 5 LEDs in series with one resistor in series with each row (and all rows in parallel). Or, to compensate the differences between the LEDs I-V characteristics you could use a constant current source to drive them

And you should tell us the applied input voltage. Make sure it's sufficient enough for the voltage of the series diode-coloumns.

Maybe this helps:
http://www.hebeiltd.com.cn/img/one_res_many_leds_series.gif

my Input voltage is a converted 12V AC-DC supply..... @Calinoaia, I tried out your suggestion it gave the same result as complained earlier....@ Collin Mitchel, I printed out and read the whole of that article on talkingelectronics.com before coming here, what i am made to understand is that different colours mean different voltage drop hence the need to compensate for the drops of each LED with a resistor on a lower drop line.... But the thing is that, since we are placing these LED's in parallel it means we are placing them in a current divider circuit hence the more the amount of LED in parallel the lesser the current (resistor being constant), right?.....so should I just place enough LED in parallel just enough to make them have max brightness and then place another parallel in series with the first or what? cos I think I tried that before and turned out the same....

@collin, sorry for not understanding properly, But the truth is that I have seen projects with over 4000 LEDs..... would they test each LED for their characteristic voltage in forward bias or is there some other way

yep I got it, used same colour LEDs in parallel, means equal voltage drop, hence could power over 20 LED

In case anyone hits on this discussion from a search (or something) I offer the following: Because this question "How to power an LED" comes up so often I decided to do a blog on the subject. Here's the URL:

* www.sinistercircuits.com/Blog/LEDs_LightemWithoutSmokinem