Would really appreciate some help guys!

[tony100]

Hi All
I need a circuit diagram for a 10x10 hi brite red led array, where the forward voltage is 2.1v and 20ma current draw. Can this be operated from a 12v or maybe a 24v source? I also need a circuit for same array config blue leds, 3.6v and 30ma. Since this will be operated from a power supply, current drain is not important (not batteries) Should I incorporate any type of cooling? (fan).

Thanx a mill

tony100

 

[MikeMl]

24V is better. Is 2.1V the max forward drop, or the average forward drop?

If the forward drop is 2.1V per LED, and the supply is 24V, you would like to have several LEDs in series, sharing one current limiting resistor.
If you have 10 LEDs in series, that would 21V across the LEDs, leaving 3V across the resistor. Since you want 20mA, the resistor is E/I = 3/0.02 = 150Ω

The power rating of the resistor is E^2/R = 3*3/150 = 0.06W, so a 1/4W resistor would work fine...

Repeat 10 times...

 

[Diver300]

For the blue LEDs, I suggest 5 in series, with a 200 Ω, 0.5 W resistor in series. 20 repeats.

You could go to 6 in series, and an 80 Ω resistor. However the current would vary more if the forward voltage isn't exactly 3.6 V. You would need 15 strings like that, and two strings with 5 LEDs.

You can always increase the resistor value to a more easily obtainable value. With 220 Ω for the 5 LEDs or 82 Ω (or even 100 Ω) for the 6 LEDs, you won't notice the difference in brightness.

 

[HarveyH42]

Here's a link to a very good array calculator, should be just what you need.

**broken link removed**

Red + Blue = police lights? Next question, flash pattern circuit?

 

[tony100]

tony100

Thanks to HarveyH42, Diver300, MikeMl,

Problem solved, thanks Mike for the little lesson (Ohms law) your suggestion for strings of
10 is perfect, and i will use that.
The led wizard seems to work well, and has suggested strings of 5 blue leds with a 220Ω
resistor in series which i will use.

Once again thank you all.

Incidentally the cops only use blue in this neck of the woods Harvey! (Cape Town ZA)

 

[HarveyH42]

Thanks to HarveyH42, Diver300, MikeMl,

Problem solved, thanks Mike for the little lesson (Ohms law) your suggestion for strings of
10 is perfect, and i will use that.
The led wizard seems to work well, and has suggested strings of 5 blue leds with a 220Ω
resistor in series which i will use.

Once again thank you all.

Incidentally the cops only use blue in this neck of the woods Harvey! (Cape Town ZA)

Was just a guess. We see a lot of requests for police light type projects. Didn't see a locations...