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Current Amplification

Discussion in 'General Electronics Discussion' started by Marco203, Aug 2, 2016.

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  1. Marco203

    Marco203

    3
    0
    Aug 2, 2016
    Hello,
    I have a function generator to generate a sinusoidal voltage waveform (+5-5 V) and a coil. I have to design a circuit that allows to change AMPLITUDE and FREQUENCY of the current flowing in the coil. To amplify current I have a transistor (MJE) (both pnp and npn). How should I design the circuit?
    I'm using LTspice as simulator.

    Thank you

    Marc
     
  2. Alec_t

    Alec_t

    2,985
    811
    Jul 7, 2015
    Welcome to EP!
    As this is a Homework question, show us your best efforts so far at a design, then we can give guidance.
     
  3. Marco203

    Marco203

    3
    0
    Aug 2, 2016
    upload_2016-8-2_17-52-18.png
    this is what I have so far. I don't know how to have an alternating current in the coil where I can change its frequency and amplitude
     
  4. AnalogKid

    AnalogKid

    2,526
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    Jun 10, 2015
    I think you should check with the instructor about the requirement to change the frequency. That is very difficult. For example, if you have a 1.0 kHz input frequency and you want to change it to 1.2 kHz, you can heterodyne it with a 200 Hz signal in an analog multiplier. This sounds like it is way beyond the level of the course.

    ak
     
  5. Marco203

    Marco203

    3
    0
    Aug 2, 2016
    well, so just focusing on the transistor, how can I know how to have a precise alternating current (like +1/-1 Amperes) flowing into the coil, given the sinusoidal voltage in input? the coil is represented in spice with a resistance and an inductance in series.
    thanks
     
  6. AnalogKid

    AnalogKid

    2,526
    718
    Jun 10, 2015
    For precision you must have a feedback circuit that compares the current into the coil against a reference value. The forward gain of a single transistor varies significantly with temperature and with collector current. I don't think you can get "precise" current regulation out of any variation of the circuit in post #3.

    What part of Italy?

    ak
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    652
    May 8, 2012
    My guess is that your instructor requires that the circuit be capable of functioning over an audio frequency spectrum that can be changed via the signal generator. It's either that or your instructor is also expecting you to build a variable frequency signal source but I doubt it.

    I would also suggest that you Google "Push-Pull Amplifier Circuit" and "Complimentary Symmetry Amplifier Circuit".

    Chris
     
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