Help with current amplification

Discussion in 'The Projects Forum' started by ShreyasPradhan, Oct 28, 2013.

  1. ShreyasPradhan

    Thread Starter New Member

    Aug 16, 2013
    5
    0
    Hi,
    I am fairly new to electronics. I am working on a project relating to APD measurements. I have connected the APD in the reverse bias mode with 100V DC. I am getting a low current out of it; hence i wish to amplify the same. For the current amplification i am using 2222n transistors in darlington pair mode. But i am not getting any amplification. I have attached the schematic of the circuit. Please help me out with the connections. Are my connections right? I am not sure where to connect the two terminals of the input and from where to take the output. I have connected the 2nd terminal of the input to the emitter and am taking the output from the collector and the emitter. Please guide. Thanks in advance.
     
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Not sure what a APD is so I'll leave the input part.

    Current is measured Through something, Not Across.

    In your sketch, you have defined the Output across the circuit; you will get a constant 9 Volts reading.

    In principle, you can measure the current directly using a milliammeter in series with the power supply,]

    or else,

    put a resistor of, say 10 KΩ in series with the power supply and measure the voltage across the resistor.

    Ramesh
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    After some though I realize APD must refer to an Avalanche PhotoDiode, but it would be nice if you would spell it out in your post so we wouldn't have to do any mental gyrations to come up with that. :rolleyes:

    Your circuit won't work. As Ramussons noted you are simply measuring the supply voltage. You need a resistor in series with the collector to the power supply to provide voltage amplification of the transistor collector current. And eliminate the emitter resistor as it serves no purpose here.

    But a better way to amplify an APD signal is to use an op amp connected as a transimpedance amplifier.
     
  4. ShreyasPradhan

    Thread Starter New Member

    Aug 16, 2013
    5
    0
    I apologize for the inconvenience. Yes APD is avalanche photodiode; and i wish to amplify the output current. How should i go about it? Where should i connect the anode and the cathode. Will it be better to first amplify the current and then convert it to voltage through transimpedance amplifier?
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    A transimpedance amplifier is the best and most common way to amplify he current from an APD and convert it to a voltage. Here are some example circuits.
     
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