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IR diode looks photovoltaic outdoor

Discussion in 'Electronic Design' started by blisca, Feb 15, 2007.

  1. blisca

    blisca Guest

    hi,
    i'm doing a little experience with infrared emission,reception modulation
    etc

    eventough my system(very primitive) works fine indoor it is not the same
    outdoor,it looks that the sfh250 Ir receiving diode when exposed to the weak
    winter sun of northern Italy is able to generate about
    -400 mV on a 1MOhm load

    What is it due to? and how can i avoid it if possible?Shielding?Red glass
    filtering or what ??Thank you

    Diego
    Italy
     
  2. Paul Mathews

    Paul Mathews Guest

    Photodiodes produce current. Resistors create voltage drop
    proportional to current. The usual remedies:

    1) reduce load resistance, which also reduces sensitivity, of course
    2) apply reverse bias voltage, which may require capacitive coupling
    if the amplifier circuit is sensitive to DC level
    3) use a transconductance amplifier, which can be configured to keep
    voltage across the photodiode near zero volts

    Paul Mathews
     
  3. blisca

    blisca Guest



    thank you,very much,at first

    in the past days i used a TSOP1736,integrating filters ,demodulation and so
    on

    his feature should be high immunity to environmental light,but while exposed
    to the sun passing fast the hand and shadowing it quickly seems enough to
    turn it's output active

    strange,not?
     
  4. Paul Mathews

    Paul Mathews Guest

    Integrated IR photodetectors such as TSOP1736 usually include an
    optical filter that reduces effects of ambient light. However, they
    are not really designed to operate in daylight, since most people
    don't watch TV in daylight. Typically, their field of view is reduced
    by some type of aperture or tube placed in front of the photodetector.
    IR remote controls emit intense beams, and the 'commands' are
    repeated, with the user re-aiming the remote, until the desired
    results are achieved. You can use and aperture, tube, or lens to
    narrow the field of view.
    Paul Mathews
     
  5. Al

    Al Guest

    Use two photodiodes. Aim one at your source, the other someplace else
    neutral. Use a differential input and subtract one from the other.

    Al
     
  6. redbelly

    redbelly Guest

    What will also work, and be simpler, is to wire the two photodiodes
    together, in parallel but with opposite polarity. (cathode of one to
    the anode of the other, and vice versa).

    That way, the two should act as a single differential current source,
    requiring just a single amplifier or current-to-voltage converter.

    My coworkers and I used such a configuration years ago for a laser
    spectroscopy measurement.

    Mark
     
  7. blisca

    blisca Guest

    the fact is that the receiving circuit is mounted on a vehicle in a race
    track
    so i think that is difficult to separate useful signals from the "light
    floor"
    i'm not shure it will work in my case but it looks interesting
    Every time lot of things hint and ideas from the NG,thank you sincerely
     
  8. redbelly

    redbelly Guest

    Can you use a smaller load resistor? To avoid saturating the
    photodiode, the voltage should not be higher than about 250 mV or so.

    Mark
     
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