Urgent with photodiode.

Discussion in 'The Projects Forum' started by ShreyasPradhan, Aug 20, 2013.

  1. ShreyasPradhan

    Thread Starter New Member

    Aug 16, 2013
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    Hi. i am working with BPW21R photodiode. I am controlling the output using LED as an illuminating source and controlling it by pulse width modulation. I need to amplify the photodiode output current upto 1.5 amperes - 2 amperes. I have 2N3055 power transistors and have used them in darlington pair configuration. Still i am not getting sufficient current. I finally wish to use this current to drive a IR laser diode which requires 2V and 1.5 Ampere current. Please guide me on how should i amplify it.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    The 2N3055 is a pretty beefy transistor, it is just damn slow!

    A complete description of your project would help us help you. What are you trying to accomplish? A remote light show (relatively slow signals) or digital communications (relatively fast signals)?

    And welcome to the forums!
     
  3. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,127
    266
    I would switch to a N-ch power MOSFET.

    The FET will be so much easier to drive, more efficient, more compact.
     
  4. ShreyasPradhan

    Thread Starter New Member

    Aug 16, 2013
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    I wish to drive an IR laser diode and use it as a heating element. i am performing a reaction in which i need to produce 3 different temperatures for specific amount of time. I am planning to do this by controlling the laser output via a change in voltage. This change in voltage i am planning to achieve by incorporating the voltage changes in photodiode output. This photo diode output i have to amplify till 1-2 amperes and feed it in the laser diode. I am not able to get proper required amplification. Am i right in the approach; or is there a better way to control the laser output which you can suggest. Any help is much appreciated.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Wow, it must be something very small you are trying to heat!?

    So... the photo diode is the temperature feedback? am I right?

    If this is true, you must measure the temp between laser heating pulses to avoid unwanted feedback in the loop?
     
  6. ShreyasPradhan

    Thread Starter New Member

    Aug 16, 2013
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    Yes, its a very small surface i need to heat. The photodiode output is the input voltage for the laser. I need that to be amplified so that can be used to drive the laser diode.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    +1 There are many possible solutions but they're not worth talking about without knowing more details.

    My prediction is that your 2N3055 is not working for you because you are not supply enough current to its base. If you need the 2N3055 to pass 2A, for instance, you can estimate that you need 0.2A in its base.

    That's all I can guess without seeing a schematic.
     
  8. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    Is this, "urgent" enough to tell us how fast you need to change temperatures?
     
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