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Re: Photodiode installed polarity?

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  • Dave
    They are desingned to be used in reverse bias. Sounds like that that one is wired correctly, but unless you take a meter and read a positive voltage to the
    Message 1 of 7 , Jan 29, 2013
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      They are desingned to be used in reverse bias. Sounds like that that one is wired correctly, but unless you take a meter and read a positive voltage to the same "ground", you cannot know by looking. That voltage is what gets affected by seeing the light emitter or not, so with a voltmeter, it is easy to see if it is working. Just put the meter across the diode and allow or block the light, and watch for the change. Some digital meters are excruciatingly slow, so give it a couple seconds.

      -fab

      --- In Electronics_101@yahoogroups.com, Dave C wrote:
      >
      > A photodiode in a large commercial paper shredder detects IR emitted from an IR LED and signals the cutters to start when IR is interrupted by a document inserted.
      >
      > I'm looking over the circuit and the photodiode is wired with the anode to ground.
      >
      > I have no wiring diagram.
      >
      > Should A or K be negative?
      >
      > Thanks,
      > Dave
      >
    • Stefan Trethan
      Photodiodes can be used both ways, reverse biased or as a solar cell. Dave, you still working on that same shredder? ST
      Message 2 of 7 , Jan 29, 2013
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        Photodiodes can be used both ways, reverse biased or as a solar cell.

        Dave, you still working on that same shredder?

        ST



        On Tue, Jan 29, 2013 at 1:09 PM, Dave <dkosewick@...> wrote:
        > They are desingned to be used in reverse bias. Sounds like that that one is wired correctly, but unless you take a meter and read a positive voltage to the same "ground", you cannot know by looking. That voltage is what gets affected by seeing the light emitter or not, so with a voltmeter, it is easy to see if it is working. Just put the meter across the diode and allow or block the light, and watch for the change. Some digital meters are excruciatingly slow, so give it a couple seconds.
        >
        > -fab
        >
        > --- In Electronics_101@yahoogroups.com, Dave C wrote:
        >>
        >> A photodiode in a large commercial paper shredder detects IR emitted from an IR LED and signals the cutters to start when IR is interrupted by a document inserted.
        >>
        >> I'm looking over the circuit and the photodiode is wired with the anode to ground.
        >>
        >> I have no wiring diagram.
        >>
        >> Should A or K be negative?
        >>
        >> Thanks,
        >> Dave
        >>
        >
        >
        >
        >
        > ------------------------------------
        >
        > Please trim excess when replyingYahoo! Groups Links
        >
        >
        >
      • Larry Beaty
        The photo diode should be reversed biased. Larry From: Electronics_101@yahoogroups.com [mailto:Electronics_101@yahoogroups.com] On Behalf Of Dave C Sent:
        Message 3 of 7 , Jan 29, 2013
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          The photo diode should be reversed biased.



          Larry



          From: Electronics_101@yahoogroups.com
          [mailto:Electronics_101@yahoogroups.com] On Behalf Of Dave C
          Sent: Tuesday, January 29, 2013 12:39 AM
          To: Electronics101
          Subject: [Electronics_101] Photodiode installed polarity?





          A photodiode in a large commercial paper shredder detects IR emitted from an
          IR LED and signals the cutters to start when IR is interrupted by a document
          inserted.

          I'm looking over the circuit and the photodiode is wired with the anode to
          ground.

          I have no wiring diagram.

          Should A or K be negative?

          Thanks,
          Dave





          [Non-text portions of this message have been removed]
        • Dave C
          Photodiodes can be used both ways, reverse biased or as a solar cell. Thanks. Dave, you still working on that same shredder? ST Yes Stefan, getting back to it.
          Message 4 of 7 , Jan 29, 2013
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            Photodiodes can be used both ways, reverse biased or as a solar cell.

            Thanks.

            Dave, you still working on that same shredder?

            ST

            Yes Stefan, getting back to it. It's my new year resolution...

            Dave

            [Non-text portions of this message have been removed]
          • Kerim F
            Well... a photodiode could be biased with 0V (actually very close to zero) when used in an opamp inverting amplifier.
            Message 5 of 7 , Jan 29, 2013
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              Well... a photodiode could be biased with 0V (actually very close to zero) when used in an opamp inverting amplifier.

              --- In Electronics_101@yahoogroups.com, "Larry Beaty" wrote:
              >
              > The photo diode should be reversed biased.
              >
              >
              >
              > Larry
              >
              >
              >
              > From: Electronics_101@yahoogroups.com
              > [mailto:Electronics_101@yahoogroups.com] On Behalf Of Dave C
              > Sent: Tuesday, January 29, 2013 12:39 AM
              > To: Electronics101
              > Subject: [Electronics_101] Photodiode installed polarity?
              >
              >
              >
              >
              >
              > A photodiode in a large commercial paper shredder detects IR emitted from an
              > IR LED and signals the cutters to start when IR is interrupted by a document
              > inserted.
              >
              > I'm looking over the circuit and the photodiode is wired with the anode to
              > ground.
              >
              > I have no wiring diagram.
              >
              > Should A or K be negative?
              >
              > Thanks,
              > Dave
              >
              >
              >
              >
              >
              > [Non-text portions of this message have been removed]
              >
            • smilingcat90254
              Well lets get few things straightened out here. You can run the photodiode in one of two modes. As a solar cell, aka photovoltaic mode. No bias voltage is
              Message 6 of 7 , Jan 30, 2013
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                Well lets get few things straightened out here.

                You can run the photodiode in one of two modes. As a solar cell, aka photovoltaic mode. No bias voltage is applied and the diode generates its own open circuit voltage. This mode has its application.

                Second mode of operation is called photoconductive mode. The diode is reverse biased. This mode is used for fiber optic communication where hi-speed response is very important.

                There are other reasons for choosing one mode or the other, but both modes of operation have their advantages and disadvantages.

                Photoconductive mode is bit harder to understand; but, it is used widely. You can find reference design in Burr-Brown, Analog Devices and Linear Tech.
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