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BPW34 & Rail to Rail OpAmp

Discussion in 'General Electronics Discussion' started by Ben Halicki, Sep 3, 2015.

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  1. Ben Halicki

    Ben Halicki

    10
    1
    Sep 3, 2015
    Hi Guys,

    I have limited electronics experience but looking to build a basic light sensor and looking for suggestions on what opamp to use.

    I am using a silicon photodiode BPW34, which produces around 200mV in low light. I need a rail to rail opamp that operates from a 5V supply. I want to be able to adjust the gain so at similar light levels I read 5V on the opamp output (when the photodiode is producing 200mV). I want a linear output based on input voltage (not a comparitor).

    Hoping someone can suggest a suitable part that is easily obtainable (preferably at somewhere like Jaycar).

    Thanks in advance,

    Ben.
     
  2. Old Steve

    Old Steve

    734
    169
    Jul 23, 2015
    Ben, did you find one yet? Offhand, I can't point you directly to one that'll fit the bill and is also available from Jaycar or Altronics, but if you check out RS Components AU, you can select supply type, (single supply), and output type, (rail-to-rail), in the drop-down boxes on the left of the page. :cool:
    N.B. Assuming you're after through-hole, also selecting PDIP in the drop-down boxes will narrow the search results considerably. I get 59 results with those filters.
    Here:-
    http://au.rs-online.com/web/c/semiconductors/amplifiers-comparators/operational-amplifiers/

    RS have free (and very fast, I might add) delivery for all online orders these days, so delivery won't cost an arm and a leg. Personally, I try to be a bit decent about that, and order as much stuff as possible in each order. Your chance to stock up. :D
     
    Last edited: Sep 3, 2015
  3. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Check Microchip. They have a good selection of rail-to-rail opamps that operate at 5V.

    Bob
     
  4. Ben Halicki

    Ben Halicki

    10
    1
    Sep 3, 2015
    Thanks very much Steve and Bob, that has helped me a lot. Appreciate the feedback.

    Kind regards,

    Ben.
     
  5. paofanello

    paofanello

    3
    0
    Jul 16, 2015
    [​IMG]
    Look at something like this to amplify the signal of the photodiode!
    Amplify directly its voltage is not advised.
     
  6. Ben Halicki

    Ben Halicki

    10
    1
    Sep 3, 2015
    Hi Paofanello, thanks for the tips. I have found some circuits as you describe, would you mind explaining why it's not a good idea to amplify the voltage directly (as the circuit above shows)? I should have added that I want to run the op-amp from a single supply.. i'm not sure how to do this yet, but should probably read a bit more on how op-amps work I guess.

    Steve thanks again for the tips on RS... I wasn't aware they were offering free freight, could be a double edged sword, all too easy to stock up now :)
     
  7. paofanello

    paofanello

    3
    0
    Jul 16, 2015
    Ok... first of all: I'm italian and i'm sorry if my english is not perfect (or orrible :))
    The issue is this: photodiodes "turn" the light that they recivied in CURRENT, the voltage is only a consequence, so if you want a linear response between light and the signal you have to amplify the current of the photodiode.
    I don't understand: you think that the this circuit amplify the voltage?
    [​IMG]

    This circuit above is called a transimpedance amplifier: it turns a current signal in a voltage signal, and the resistor set the gain, if you choose the right resistor you can obtain the effect you want.
     
  8. paofanello

    paofanello

    3
    0
    Jul 16, 2015
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