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TER
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2020/05/15 05:16:17 (permalink)
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An output impedance of amplifier

I want to understand an output impedance of amplifier. I read many articles about it, but i didn't understand. Any help please!!!
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    JPortici
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    Re: An output impedance of amplifier 2020/05/15 07:36:41 (permalink)
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    how is this even REMOTELY related to programming specifications of 16bit microcontrollers?
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    LdB_ECM
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    Re: An output impedance of amplifier 2020/05/15 07:49:55 (permalink)
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    It's simply the highest voltage at the largest current the amplifier can drive without distorting the signal by a set amount usually measured as total harmonic distortion (THD).
     
    You should know the formula V= IR .... For AC signals Resistance R becomes Impedance Z and so
    V= IZ    or as we want Z    ... Z = V/I
     
    So the smallest impedance an amplifier can drive is the largest undistorted voltage (Vmax) divided by largest undistorted current (Imax).
     
    So Zmin = Vmax/Imax
     
    It is obvious on sound systems as the Impedance of the speaker is fixed the only way to make it louder is to increase the voltage output. At some point that will lead to the situation the amplifier output current reaches a point it starts to distort or the waveform reaches or the output voltage that exceeds the peak to peak rating. Whichever happens first creates the minimum impedance the amplifier can drive.
     
    Speakers are generally design around certain fixed impedance standards 8,16 etc. So generally the louder you want them the higher the output amplifier voltage has to go which is done by varying the gain somewhere along the amplifier stage. That should give you enough to understand.
     
    Works the same on Digital IO .. if an I/O pin can drive 10ma at 3.3V
    ZMin = 3.3V/0.01A = 330 Ohms.
    So that IO pin can't drive a load lower than 330 ohms.
    post edited by LdB_ECM - 2020/05/15 08:07:12
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    TER
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    Re: An output impedance of amplifier 2020/05/27 03:44:38 (permalink)
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    I want to thank You!
    so I have one question.
    I have Class A amplifier and Pic24 microcontroller , how matches their input and output impedance ? 
    #4
    ric
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    Re: An output impedance of amplifier 2020/05/27 03:51:08 (permalink)
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    termin
    I have Class A amplifier

    That's not nearly enough information.
    You'd need to supply a schematic and data for the output drivers etc.
     

    and Pic24 microcontroller ,

    what PIC24 microcontroller?
    Connected how?
    Why are you being so stingy with details?


     

    I also post at: PicForum
    Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
    NEW USERS: Posting images, links and code - workaround for restrictions.
    To get a useful answer, always state which PIC you are using!
    #5
    LdB_ECM
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    Re: An output impedance of amplifier 2020/05/27 05:51:23 (permalink)
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    Any amplifier kit will have a quoted input impedance or max voltage, the class doesn't matter.
    If they only quote the maximum voltage you can assume the input impedance is high (AKA greater than 10K) 
     
    Now all micro-controller DAC tend to work on the MCU supply voltages of 3.3V or 5V etc so their output voltage is high but there output impedance is also usually high. The DAC on the PIC24F range are typically around 3K.
    So you can safely drive any amp with higher than that input impedance. However usually the safe step to do is take the output into a good rail-to-rail op-amp setup as a unity follower the benefit is you can then get around using small signal amplifiers.
     
    This is an old microchip note for 8 bit DAC but it show you the unity follower buffer
    https://microchipdeveloper.com/8bit:dac
    The op-amp in this format has massive input impedance in the Mega-Ohm range so puts no load on the DAC output. On the other side you then have the low output impedance of the op-amp which will be quoted on the datasheet. That will generally be enough to drive headphones or take out to a power amp if you want more noise.
     
    #6
    crosland
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    Re: An output impedance of amplifier 2020/05/27 08:19:00 (permalink)
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    If the OP is concerned about the output impedance of the amplifier then I suspect he wants to connect it to a PIC input.
     
    That would sugest he's interested in the ADC, not the DAC.
    #7
    LdB_ECM
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    Re: An output impedance of amplifier 2020/05/27 10:08:30 (permalink)
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    I am dubious the input impedance of the PIC24F is 2.3K anything but the smallest of small signal amplifiers will exceed that. Actually having any amplifier on the input would be one up from what the hobbiest usually do :-)
    #8
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