1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

LED light

  1. Sep 14, 2008 #1
    Can anyone explain to me why LED2 light only half time compared to LED1? If Us=2sinωt volts

    Attached Files:

  2. jcsd
  3. Sep 14, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Think about what the transistor does when Vs is "high".
  4. Sep 15, 2008 #3
    it doesn't help me a lot...
  5. Sep 15, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    That's okay, we'll review how the transistor functions in this circuit.

    The transistor has 3 nodes:
    The Base (left side of transistor)
    The Emitter (lower-right of transistor)
    The Collector (upper-right of transistor)

    In this circuit, the transistor acts like a simple switch. When the Base voltage is high, you can treat it as a short between the Emitter and Collector. Which LED or LED's have any appreciable current going through them, if you short the Emitter to the Collector?

    When the Base voltage is low or negative, you can treat the Emitter to Collector as an open circuit, with no appreciable current. If that's the case, which LED or LED's have an appreciable current going throw them?
  6. Sep 15, 2008 #5
    I understand it now. Thx for the help!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: LED light
  1. Led lighting (Replies: 9)

  2. LED lighting and RFI (Replies: 1)

  3. LED grow light (Replies: 47)