Run a string of LEDs from the mains


Results 1 to 31 of 31

Threaded View

  1. #27
    Join Date
    Nov 2003
    Location
    Greece
    Posts
    4,170


    Did you find this post helpful? Yes | No

    Default

    Quote Originally Posted by The Master View Post
    How do i run the LEDs at 30mA instead of 50mA. Im lead to believe that if i use, for example, 5 LEDs on 12V instead of 4 then obviously the voltage drops but the current is supposed to drop too.
    1. How do you run at 50mA ? The same way at 30mA.

    2. What do you mean the voltage drops? Every LED needs a forward voltage of about 3.4 volts and the current should stay about 30mA. So if your source is 12 Volts then your resistor which should always considered there has to drop the rest of thevoltage that is 12-3.4=8.6 and its vaue would be 8.6/.03=286.6 ohms

    Now if you want in series more leds, thats OK. put up to 3, and 3 x 3.4 = 10.2 volts. The rest should be dropped on the resistor in series. You cannot omit the resistor and put another LED. Chances are that they will not light.

    Why? The answer is simple. Look at the characteristic curve of a diode (or LED, its the same). It conducts the forward voltage at a very specific point and increasing the voltage slightly, the current increases dramaticaly. I said that on my previous post but you did not give it attention.

    Look at the attached photo.

    Ioannis
    Attached Images Attached Images  
    Last edited by Ioannis; - 30th September 2009 at 19:26.

Similar Threads

  1. How about String Variables?
    By mytekcontrols in forum PBP Wish List
    Replies: 40
    Last Post: - 20th January 2015, 12:53
  2. Embedded Strings in your Code Space
    By mytekcontrols in forum mel PIC BASIC Pro
    Replies: 49
    Last Post: - 9th March 2008, 07:50
  3. Using LEDs as light sensors
    By skimask in forum Code Examples
    Replies: 3
    Last Post: - 30th December 2006, 22:19
  4. Visual Basic 6 & Access 2000
    By Demon in forum Off Topic
    Replies: 33
    Last Post: - 7th September 2006, 04:39
  5. controlling leds with the switches
    By ilteris in forum mel PIC BASIC Pro
    Replies: 2
    Last Post: - 12th October 2005, 21:02

Members who have read this thread : 0

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts