What is the difference between irLED and photodiode?

Discussion in 'General Electronics Chat' started by PowerLogic, Jan 20, 2015.

  1. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    Sir,

    What is the difference between infrared LED to a photodiode?
    a photodiode can be replace with infrared led and the same with infrared led to a photodiode?

    hoping your best response
    thanks a lot!
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,757
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    And what does this have to do with resistors getting too hot?

    Please don't hijack someone else's thread; start your own.

    I'll report your post to the mods so that they can split it off into its own thread. They'll probably take care of very shortly and then we can answer your question there.
     
  3. PowerLogic

    Thread Starter New Member

    Jan 7, 2015
    8
    2
    i,m sorry
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Not a problem -- live and learn.
     
  5. WBahn

    Moderator

    Mar 31, 2012
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    An infrared LED is a light EMITTING diode.

    A photodiode is a device that conducts reverse electrical current in response to light being ASBORBED by it.

    Two very different devices and, no, you can't replace one with the other.
     
  6. harry85

    New Member

    Jan 21, 2015
    5
    1
    LED is stand for light EMITTING diode and it is type of diode.
     
  7. Reloadron

    Active Member

    Jan 15, 2015
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    Yes, both the photodiode and light emitting diode are semiconductor devices.

    Taken from the Wiki:
    "A photodiode is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode. A small amount of current is also produced when no light is present. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas".

    "A light-emitting diode (LED) is a two-lead semiconductor light source. It is a pn-junction diode, which emits light when activated".

    Note that if I use my DMM and place the leads across a LED and shine a light source on the LED I will measure a small voltage.

    Ron
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The technical author Forrest Mims III likes to point out that LEDs make light detectors if you shine light on them. Preferrably of the same or slighly shorter wavelength than they emit. They make fair sensors and actually have pretty fast response times - essentially acting as a photodiode.

    However, that is more of a novelty of LEDs (including IR LEDs) than a designed function. A photo-diode that is desgined as a light detector is much more sensitive and faster response time than a simple LED. There are detials of LED design that make them more than just a PN junction - quantum wells, doping transitions, doping concentrations, and specific chemistry (gallium, phosphorius, aluminum, nitrogen, ...).

    A simple LED sensor can be made by connecting a 100k resistor to the anode of an LED. Connect other end of resistor to ground. Connect Cathode to ground. Measure voltage at the resistor-LED node.

    Cheers.
     
    cmartinez and Reloadron like this.
  9. Reloadron

    Active Member

    Jan 15, 2015
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    Maybe I should have been more in detail as to that. If you want light select a component that emits light and if you want to detect light use a component designed to detect light.

    Ron
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    Pretty much all PN junctions (I think it's actually 'all', but am leaving some wiggle room there) are photosensitive and will behave as photodiodes. If you decap an old memory chip you can actually use it as an imager (newer ones have too many metal layers over the silicon to do this well). Most diodes are encapsulated such that light cannot get to the junction. This is pretty much impossible with an LED since you need light to be able to get OUT of the junction.
     
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