Darlington Pair using BC 547

Discussion in 'General Electronics Chat' started by pal114525, Jul 4, 2015.

  1. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Would you be kind to tell me if I can use two BC547 transistor to design a darlington pair amplifier?

    Thanks & Regards.
     
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Yes is the short answer
     
  3. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,
    Thanks for your valuable feedback.
    Would you be kind to tell me the following point?

    I need 500mA current to pass through a rectangular coil to create an EM field.
    My input is 3V sinusoidal wave with frequency 16KHz and the current is very low ( Generated from a Hartley oscillator). I want to amplify this current to ~500mA.
    Shall I use a darlington pair amplifier or shall I use a push-pull amplifier along with a preamplifier? Which one would be the best suitable for this?

    Thanks & Regards.
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Please post more information, as in, inductance of the coil, voltages, a block diagram that shows signals, amplitudes and signal flow. Your description is vague, please clarify.
     
  5. absf

    Senior Member

    Dec 29, 2010
    1,492
    372
    From the datasheet of BC547, the maximum Ic=100mA and Icm=200mA. So even you connect them in Darlington pair, the output can never exceed its max current though the combined gain is very high. Take a look at the BC547 pdf attached.
     
    cmartinez likes this.
  6. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Please see the attachment.
    My input to the amplifier is 3V sinusoidal wave with frequency 16KHz and the current is very low ( Generated from a Hartley oscillator). I want to amplify this current to ~500mA.
    Shall I use a darlington pair amplifier or shall I use a push-pull amplifier along with a preamplifier? Which one would be the best suitable for this?

    Thanks & Regards.
     
    • TX1.png
      TX1.png
      File size:
      19.8 KB
      Views:
      20
  7. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    To drive that amount of current into a coil at 16kHz will likely require a push-pull amplifier.
    What is the coil resistance and inductance? Without that info we can't help any further.
     
    pal114525 likes this.
  8. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Thanks for your valuable feedback.
    The inductance of the coil is 458 uH.

    With Regards.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    That answers half my question. :rolleyes:
    What's the coil resistance?
     
    pal114525 likes this.
  10. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Thanks for your valuable feedback.
    Coil resistance is 10 ohm.

    With Regards.
     
  11. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    That would be about 2.5 Watts. (500 mA X 500 mA X 10 Ohms)
    There are a lot of audio amplifier circuits that will do that for you.

    Bertus
     
    pal114525 likes this.
  12. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Thanks for your valuable feedback.
    Would you be kind to explain me the following point?
    1. How to determine the value of resistors for a typical Class B push -pull amplifier?

    Thanks & Regards.
     
  13. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    You could have a look at a power-opamp like the LM675.

    Bertus
     
    pal114525 likes this.
  14. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Thanks for your valuable feedback.
    LM675 uses supply voltage range from 16V to 60V. In my design, the supply voltage is 12V.
    Would you be kind to tell me if there is any other way of current amplification of the order ~500mA?

    Thanks & Regards.
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,538
    1,251
    At 16 kHz the coil inductive reactance is j46 ohms. The complex impedance vector is 47 ohms.

    ak
     
    cmartinez likes this.
  16. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    To get 0.5A peak current at 16kHz through a 458uH coil you need roughly 24V peak wave. I you would have to quadruple your 12v supply voltage to get that 48Vpp required.
     
  18. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,
    Thanks for your valuable feedback.
    With regards.
     
  19. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    If you add a 220nF in series with the coil it will be resonant at near 16kHz.
    Driving that with a 0-12V, 16kHz square-wave showed a peak inductor current of about 350mA in simulation.
    To get more current you could drive the resonant circuit with a push-pull audio bridge circuit such as the TDA2005, which would near double the supply voltage across the load (about 20Vpp with a 12V supply).
    That should give a maximum peak current in the resonant circuit (220nF in series with the coil) of over 600mA.

    Edit: If you can tolerate some frequency deviation then you could add a series capacitor to form a resonant circuit at about 16kHz and use feedback to form a high current resonant oscillator at this resonant frequency. You can do that with a fairly simple bridge driver circuit, such as below:
    The LTspice simulation shows a peak inductor current of a little over 700mA.
    Note: R4 needs to be rated for at least 2W.

    Resonant Driver.gif
     
    Last edited: Jul 6, 2015
  20. pal114525

    Thread Starter Member

    Jul 3, 2015
    46
    0
    Hi,

    Thanks for your valuable feedback.
    Would you be kind to explain me the following point?

    1. If the inductor value (inductance) is changed from 458uH to some other (say 1.1 mH) value, then what are the components would require a change? What are the equations involved in that?

    Thanks & Regards.
     
Loading...