Photodiode current to voltage converter HELP

Discussion in 'The Projects Forum' started by dickcruz, Jan 7, 2007.

  1. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    I need a circuit breakdown on this circuit and if possible i'd like the equivalent
    stripboard schematics.
    Thanks
    URGENT
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Here is the Application Note available on National Semiconductor's website that describes the circuit you have posted.

    Figure 3 in this application note is basically the same circuit you are asking about.

    hgmjr
     
  3. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    Yeah, I am aware of that. I infact got the picture extracted out of there. I still need to know how the circuit works.
    I also want to know whether i can use a LM741 as an op amp in stead of the one shown ; and use a SLSD71N2 as the photdiode.

    I have also considered looking at the LED photometer by forrest M. but i've had moderate success in making the instrument vary output with light. How exactly does the LED act as a detctor? Any thing i should know?

    Thanks
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The photometer circuit is AC only. Look at how the components respond to the photodiode's change in conduction.

    741 op amps are pretty useless animals any more. Use an op amp with a much higher input resistance and lower leakage.
     
  5. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    Hi,
    So i can't use a stepdown trans. with a rectifier to get a 5vdc?
    What can i substitute for the op-amp??
    and
    Could someone please tell me how the circuit works?

    Thanks
     
  6. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    What exactly do you not understand about the circuit? National's application note covers the basics well enough.

    Looks to me that you can use this figure in pulsing type of applications obviously centered around 2.5V. It is also rather bulky if you are just going to use a voltage feedback amplifier.
    I understand why they have the transistor there to isolate the photodiode capactiance from the summing junction, but it seems extraneous.
    Use a blocking cap in series with the output and then rectify it.

    What are you planning to do with your rectified voltage?
     
  7. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    Ok that's what i needed i dint know what the transistor was doing there and it got me in a fix.
    I just plan to connect it to a volt meter to calculate the voltage.

    But im still not able to find a substitute for the op-amp it seems that the one in the schem. is deprecated.

    Ill need this to be able to complete the circuit.

    This is one of my first few circuits so it was hard to shift from theory to practical so would it be ok i uploaded a picture of the stripboard i soldered?

    Thanks Guys
     
  8. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    When soldered, is a photodiode electrostatically sensitive?
    Can i touch it?
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I don't understand. If this is just for a learning experience, why worry about deprication? (And why the urgency?)

    Anyway, you should be able to find a more modern voltage-feedback op amp at National's website. Try their parametric catalog: http://catalog.national.com/Cat/jsp/national.jsp
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    For that matter, an outfit called TAOS makes packaged light-to-voltage converters. They come in TO-92 packages for just about $1.25. Mouser carries them. Sensitivity goes from about 1050 nm to 240 nm. Hard to beat.
     
  11. dickcruz

    Thread Starter Member

    Jan 7, 2007
    20
    0
    What i meant to ask was : Sould it be treated as an ESSD device once its been soldered.
     
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