All About Circuits Forum How many LEDs can be put together with 12v dc supply
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#1
01-17-2009, 09:15 PM
 reno12469 Junior Member Join Date: Jan 2009 Location: Im from the US. (GMT -6) Posts: 47
How many LEDs can be put together with 12v dc supply

How many LEDs can i put together with a 12v dc supply. The LEDs are 5MM ultra bright white. They operate on 3.0-3.5Vdc, 20mA. They have a 15-25 degree viewing angle. I also want to split the number of LEDs in half and have them flash back and forth without using PIC.
#2
01-17-2009, 10:07 PM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

You can put 3 leds in series with a limiting resistor. The total current through the leds and the resistor will be 20mA. You can use as many branches of 3 leds as the power supply can power. What is the maximum current the supply can give you?
#3
01-18-2009, 02:58 AM
 Bernard Senior Member Join Date: Aug 2008 Location: Tucson AZ USA Posts: 3,199
Flashing LED's

Use a 555 chip, circuits abound in AAC, source about 6 strings and sink another 6 strings[ of 3 ea. ]. 3X 3V ea.= 9V leaving 3V to drop 3/.o2=150Ω, .o6W
#4
01-18-2009, 05:07 AM
 reno12469 Junior Member Join Date: Jan 2009 Location: Im from the US. (GMT -6) Posts: 47

its a 12 v battery
#5
01-18-2009, 05:08 AM
 thedt Junior Member Join Date: Dec 2008 Posts: 15

like car battery or a lil baby battery?
#6
01-18-2009, 09:09 AM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,069 Blog Entries: 5

Quote:
 Originally Posted by Bernard Use a 555 chip, circuits abound in AAC, source about 6 strings and sink another 6 strings[ of 3 ea. ]. 3X 3V ea.= 9V leaving 3V to drop 3/.o2=150Ω, .o6W
A straight 555 will have some trouble doing this, with 12V its positive output is 10.6VDC, due to the Darlington transistor drivers. There is just not enough voltage left over, so you'd need to reduce the number of LEDs on that side to 2, though it would drive 3 LEDs to ground. There are ways around this, are you interested?

The OP will have to give us a flash rate for me to finish determining the values of the resistors and capacitors.
Attached Images
 555 LED flasher #3.GIF (2.5 KB, 121 views)
__________________
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"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#7
01-18-2009, 04:48 PM
 reno12469 Junior Member Join Date: Jan 2009 Location: Im from the US. (GMT -6) Posts: 47

Its a car battery and i would like each one to flash once in one second.

Last edited by reno12469; 01-18-2009 at 05:00 PM.
#8
01-18-2009, 04:55 PM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

Quote:
 Originally Posted by reno12469 its a car battery
You can wire up to 1000 LEDS or more as I told you on post #2 on a small car battery.
#9
01-18-2009, 06:57 PM
 reno12469 Junior Member Join Date: Jan 2009 Location: Im from the US. (GMT -6) Posts: 47

Quote:
 Originally Posted by mik3 You can wire up to 1000 LEDS or more as I told you on post #2 on a small car battery.
Ok. But i want something like this that they flash back and fourth in one sec and using as many of the 5MM LEDs as possible in each one hooked up to the 12 v battery.

LED Strobe.JPG
#10
01-18-2009, 07:54 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,069 Blog Entries: 5

You have to upload the picture somewhere to display it in a post. AAC has good picture forums, or you can do it locally on an attachment. My blog has several tricks and tips for this, this one is what you want.

Here is a schematic that will do what you want. If you choose to add more LEDs just parallel new chains with separate resistors.

You can increase efficiency a bit by making C1 1µF, R1 10KΩ, and R2 750KΩ. It will drop the current draw from 10ma to 1ma during the alternate cycle.
Attached Images
 555 LED flasher #4.GIF (2.9 KB, 168 views)
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.

 Tags 12v, leds, put, supply

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