Audio amplifier using NAND gates?

Discussion in 'General Electronics Chat' started by electronice123, Oct 23, 2008.

  1. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
    302
    0
    I have dual frequency generators built from 4046 VCO's. The outputs of each go to a dual input NAND gate with a 10V supply voltage, this signal then goes to another dual input NAND gate (signal splits and goes to both inputs of the NAND gate) that also has a 10V supply voltage.

    I want to use the output from the NAND gate to power the base of a BJT, with a pot and resistors to control the base voltage.

    Will the NAND gates act as amplifiers in this circuit?

    What kind of transistor do I need? I want something that can carry at least 3 amps in the audio frequencies.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Gates are not amplifiers, they output either high or low logic. What exactly you want to do?
     
  3. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
    302
    0
    I just need the signal from the gate to be amplified enough to drive a transistor and be able to control the transistors base voltage with a pot.

    I was told I can use a 150K pot with a 4.7K resistor on the ground of the pot, and a 4.7 ohm resistor before the transistor to control the base voltage.

    I just don't know what kind of Op-Amp or transistor I need.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    It depends on how much you want to amplify the signal and what output power you require. By amplify you mean that you want to amplify the voltage or the current or both of them?
    Also, what is the maximum frequency of your oscillator?
    Is it outputs a square or a sine wave?
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
  6. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
    302
    0
    The maxiumm frequency is a 15kHz square wave.

    The source voltage of the amplifier is going to be 10V, I just need to be able to adjust the base voltage of the bipolar junction transistor so i can control the current flowing through the collector-emitter.

    The transistor is going to drive a indcutor with very low resistance and inductance so I need to be able to regulate the current, I figured the best way is to control the base voltage.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Yes, the most stable circuit to do that is the emitter follower configuration. What is the maximum current through the inductor?
     
  8. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
    302
    0
    The inductor is very small, actutally it's just 4 turns of 26 AWG wire wrapped between the spaces of a 3 PI inductor so as to make a small transformer.

    I think 1-3 amps at most, maybe not that mcuh, that is why I need a way to control the transistor current, either through the base voltage applied, or maybe I could use a resistance inline with the inductor.
     
    Last edited: Oct 23, 2008
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A single transistor current source is not practical for your application. A much better and still simple circuit is this one:

    http://www.ecircuitcenter.com/Circuits/curr_src1/curr_src1.htm

    Replace RL with your inductor and use a 3.5 ohms resistor for Rsense. This will give you a maximum current of about 2.5Amps, depending on the inductors resistance and the saturation voltage of the transistor. Rsense should be about 30W.
     
  10. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
    302
    0
    Awesome!

    Thanks so much for the help. I appreciate it!
     
Loading...