How to amplify 5V to 15V using a Base Common Amplifier

Discussion in 'The Projects Forum' started by zarabotkalesna, Nov 22, 2015.

  1. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    Hi guys! I want to amplify 5V to 15V using a Base Common Amplifier (because it has a high voltage gain), but I'm not succeeding... Cah you please help me? Thanks in advance.
    2015-11-22 15.24.52.jpg
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Doesn't look like a Common Base configuration to me. am I missing something?
     
  3. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    I think it's it. Feel free to change anything and give me some suggestions! :)

    Please note that the input signal is DC (USB 5V source), not AC. :)
     
    Last edited: Nov 22, 2015
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The circuit is a common base circuit.
    The Base is AC grounded by the 1 uF capacitor.
    I assume the 5 Volts source on the right is the signal input.
    It will NOT amplify the DC voltage as shown.
    It also will never reach 15 Volts on the output as the powesupply shown on the lefty is only 5 Volts.

    Bertus
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    Ib1 = 1.36 mA - 1.34 mA = 0.02mA
    I_2.46K = 1.57 mA
    I_728Ω = 1.56 mA
    Ib2 = 0.01 mA
    So why the Ib1(0.02 mA) ≠ Ib2 (0.01 mA)?
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The cap on the emitter of the transistor will block your 5VDC 'input signal'.
    You can't get 15V out of that amplifier, since its supply voltage is only 5V.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    I guess that's because all the grounded base circuits I've worked with had the base connected to GND or Vcc. I thought that blocking the supply on the right didn't make much sense as well.
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  9. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    So, is there a way that I can use my USB port as an input (which is DC), and how much voltage should I apply as Vcc (on the left in my circuit)?
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What kind of signal do you expect from the USB to amplify?
    It will not be an AC signal, like audio.

    Bertus
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    In a word, no: unless you are prepared to build a switch-mode inverter?
     
  12. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    I want a DC signal in both input and output.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Then you would need a boost regulator as Alec_t also mentioned.
    Keep in mind that the power output will NEVER be more than the input power.
    There will ALWAYS be losses in such a circuit.

    Bertus
     
  14. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    And will I achieve the same goal if I use an Op-Amp instead of Common Base Amp?
     
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For what do you want to use the created 15 Volts?
    You can amplify 5 volts to 15 volts using an opamp, but you will need a powersupply to feed the opamp.

    Bertus
     
  16. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    I have a bunch of CPU fans and I want to play with them :D
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The power output of USB will be only 300 mA and 1 A when there is a request done.
    This will likely be not enough to power the fans.

    Bertus
     
  18. zarabotkalesna

    Thread Starter New Member

    Nov 22, 2015
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    I understand. Thank you all guys!!
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Yes - the decoupling capacitor on the bottom of the base bias divider.
     
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