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Amplifier circuit help

Discussion in 'Robotics & Mechatronics' started by rakibulraju, Sep 12, 2013.

  1. rakibulraju

    rakibulraju Member

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    I have a problem with my amplifier circuit.when I measure voltage at the terminal of the dc blockin capacitor as i have given in the following picture it shows low close to zero and the frequency about 300 khz.what is the problem ?please help me someone.
     

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  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    What are you measuring with?.

    It's a really crappy 'circuit' though, and likely to generate loads of interference.
     
  3. rakibulraju

    rakibulraju Member

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    with oscilloscope which gives good measure.what should be the reason to change the frequency from 2 MHZ? please suggest me a solution
     
  4. dave

    Dave New Member

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  5. nomibucha100

    nomibucha100 New Member

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    this is very nice but good for you thanks
     
  6. tomizett

    tomizett Active Member

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    I'm not sure that the IRF510 will switch at 2MHz. If it will though, you'll need a higher current gate drive circuit - the gate capacatance of a large MOSFET causes it to sink significant current at such high frequencies, and a standard TTL output isn't up to it. You'll probaly find you need a higher voltage too - 10v is more typical.
    What's the purpose of this circuit?
     
  7. rakibulraju

    rakibulraju Member

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    'The purpose is to transfer power wirelessly.The out put of this circuit will be given to a LC circuit which will also resonate at 2Mhz.As you were saying can I give a signal from a signal generator which can give voltage 10v or above? Though according to the principle it should give the same 2 MHZ frequency at the output why it is not giving output at that frequency?I am getting about 300khz?please suggest a solution?
     
  8. BeerBelly

    BeerBelly Member

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    Make sure you drive the MOSFET hard enough. I don't have experience with the IRF510 but the IRF520 should work well at that frequency. Also try placing a 27 ohm resistor parallel with the inductor to reduce the chance of a 300khz tuned circuit at the output.
     
  9. rakibulraju

    rakibulraju Member

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    what will happen if i place a 27 ohm resistor parallel with inductor?i need 2 mhz at the output?and the theory also says that the output frequency should be 2mhz.
     
  10. tomizett

    tomizett Active Member

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    You're right that there should be no 300kHz there - the only thing I can think of is that there is a parasitic oscillation there somewhere. As BeerBelly suggests, there could be an unexpected tuned circuit disturbing the operation. Alternatively, maybe the voltage regulator is oscillating or the crystal module is being upset be such a high load?
     
  11. BeerBelly

    BeerBelly Member

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    The suggested resistor would be to lower the Q of the inductor. This would cause it to behave more like a choke and less like a tuned circuit.
     

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