Boost photodiode output voltage with transformer?

Discussion in 'The Projects Forum' started by icypenguenz, Mar 1, 2011.

  1. icypenguenz

    Thread Starter New Member

    Mar 1, 2011
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    For the design of a no-power light detector, I need to boost the output of a small photodiode array (produces 20mV @ 1uA) to 1.5V. Since a short voltage spike would be sufficient and the light source will be oscillating, shouldn't a transformer be able to do the job? I tried this with a 1:50 turn ratio transformer but didn't observe any additional output at the secondary.
    Any help would be greatly appriciated, thanks!
     
  2. K7GUH

    Member

    Jan 28, 2011
    191
    23
    Seems like an amplifier circuit would be more appropriate. The photo diode is direct current, is it not? Feeding d.c. into a transformer will get you a spike, but it will be of short duration and not carry much power. The amplifier doesn't have to be very powerful, but the 1.5 volt output has to have sufficient current to operate whatever is hooked to it.
     
  3. icypenguenz

    Thread Starter New Member

    Mar 1, 2011
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    I am trying to avoid an amp at all cost, but will use it if neccessary. I am using the 1.5V signal to wake up up a microcontroller that is in stand by. The transition from low to high is what the uC is looking for, so short duration shouldnt be a problem.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Why not use a small photocell, say one harvested from a cheap landscape light? It'd give a ton more juice than a photodiode.
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    One can obtain some very low consumption op-amps these days. Their bandwidth is rather limited, but perhaps that would not matter for this.

    http://cds.linear.com/docs/Datasheet/600345fc.pdf

    Having said that, I agree with the last poster's remark that the photo-diode output seems small. Are you trying to detect a very low light level?
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    That sounds pennywise and poundfoolish. Whatever the size of the transformer, it HAS to weigh more and consume more board space than an operational amplifier. Have you measured one lately? They're too small for me to see anymore.
     
  7. icypenguenz

    Thread Starter New Member

    Mar 1, 2011
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    Yes, I know that op-amps are quite good these days. I have one that consumes only 700nA from TI. I am trying to avoid using one since this is a "no-power" application.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    So far, it's only "no-power" because you say so. You didn't explain why you don't just use a small solar cell. Maybe charge a cap and "ping" a voltage spike if you really need that.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    What will you do if the choice is between alternatives that don't solve the problem and one that solves the problem but does not meet your requirements. Not all problems have solutions that meet our requirements. What ever convinced you there was a solution that did?
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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    I'm confused by the "no power" application. What micro-controller are you using that is a "no power" device?
     
  11. icypenguenz

    Thread Starter New Member

    Mar 1, 2011
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    You haven't heard about the new line of microcontrollers that break the laws of thermodynamics? The sensor itself needs to be "no-power". This is for a school project and there are several design constraints set by my professor. One is that there can be no external power source and another is that it must be a particular photodiode.

    Charging and discharging a cap seems like a good idea. Thank you, I will try that.
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    To quote Miracle Max: "Have fun storming the castle boys!"
     
  13. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If it were me, I'd tell the instructor I'd be happy with an 'F' for the assignment if he'd let me examine and see, in operation, the one he built


    ;)
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
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    This sounds pretty absurd. Are you able to give part numbers or references?
     
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