Why is my Opamp buffer not driving low impedance?

Discussion in 'General Electronics Chat' started by gauthamtechie, Jun 5, 2013.

  1. gauthamtechie

    Thread Starter New Member

    Mar 6, 2011
    Hi, I tried simulating a high pass filter with a load impedance(A resistor). With a High output impedance, the voltage output of my RC high pass filter doesn't change with the addition of load and with a low load impedance, it changes -that is understandable.

    So I went for an Opamp buffer. Still when I try to simulate it for a low impedance, the output voltage is clipped. Here is the image of my comparison:

    Why is this happening? How can I create a buffer to drive such low impedances?
  2. Shagas

    Active Member

    May 13, 2013
    Well I didn't look at your schematic but maybe the op amp just can't supply so much current so it clips at the point where it reaches max .
    Happened to me a few times when I was trying to have an op amp drive a 0.25 watt speaker before realising that no matter how many buffers I drive the signal through , the end stage just doesn't supply enough current
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    Take a look at this:
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Notice you have a 150 ohm resistor on the output when you show the schematic that is clipping. Most op amps cannot handle resistor loads smaller than 600 ohms. Usually a few k ohms is preferred (see Shagas' comment in post #2). You can use an audio amp (like an LM 386n (less than $1 each) if it is a low fidelity project or an LM3886 for a higher fidelity project ($6 each) - each can drive as little as 8 ohms. Alternatively, you can build a transistor driver stage. See TubeGuy's suggestion on post #3 above.
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    The answer is in the datasheet, but it's hard to find.
    See the attachments.