LED Lamp

Discussion in 'The Projects Forum' started by TastyWheat, Apr 17, 2006.

  1. TastyWheat

    Thread Starter New Member

    Apr 17, 2006
    I'm a newbie when it comes to electronics so these may be very elementary circuit questions. Correct any statements I make if they are wrong please.

    I want to make a lamp using a series of LEDs (haven't decided how many yet) that plugs into a wall socket. First off, I know that AC power is periodic which LEDs don't appreciate. I also know that diodes make the current flow one way or another. Using diodes and resistors I can make the voltage fluctuate from zero to 2.0V (or some optimum voltage) in a given LED. Now the questions:

    1) Is the period from 2.0V to 0V to 2.0V short enough that a human can't detect the LED is going on and off?

    2) If #1 is yes, does this fluctuating voltage shorten the lifespan of an LED?

    3) If #1 is no, what's a simple way to give the LED (or series of LEDs) a constant voltage?

    Feel free to just ignore my questions and post any comments you have. I'm probably missing some key points anyway.
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    You'll never see the 30 Hz flicker. Take the number of leds times 2 volts, and subtract that from the line voltage (120). Divide that number by .1 to give you the value of the current limiting resistor that will have to go in the series string. Also, you will need a 1N4004 or equivalent rectifier diode in series with the leds to block the reverse voltage - leds are not good about that. All voltages are lethal, so be careful!
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    Use some capacitor in parallel with the diodes, best at some common point for all the diodes. I don´t know the number and type of the diodes, but something like 1000uF should work. The capacitor should be rated at higher voltage than can appear in the circuit, so for example 16v if there should occur something like 8V.

    It would be better if you could provide some drawing of your circuit.
  4. TastyWheat

    Thread Starter New Member

    Apr 17, 2006
    I'll probably come back to this later. I don't actually have the time to attempt this project yet. I was thinking about a circuit using a capacitor to create a constant positive flow for the LEDs. I'm inclined to work under beenthere's assumption though, that a voltage drop won't be noticable, so I'll just use diodes and resistors. I'm not an electrical engineer so forgive me if I'm taking the easy way out.
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    hi tasty,

    here's the kind of circuit you want :D :p