How to amplify ac square wave

Discussion in 'General Electronics Chat' started by mbird, Feb 2, 2009.

  1. mbird

    Thread Starter Member

    Jan 29, 2009
    Hi --

    I have a CMOS chip and I generate a square wave with changing frequency. It is LVTTL (3.3Volt) and max current from the device is 24mA.

    I want to drive a speaker in both directions with it so I added a capacitor such that RC>>Frequency of my square wave (I think this method is called coupling capacitor?). That worked and produces a nice AC square wave -3 to 3 volts.

    Now I want to amplify this AC square wave so I can get up to 250mW for my speaker.

    I can see how to amplify current for a DC square wave with a single transistor but how do you amplify an AC square wave? Can it be done with simple transistor amplifier? Do I need an Op Amp (but looking at those it seemed like they are not the right choice for driving a speaker?)

    I did a lot of searching on the Internet for how to do this but nothing seemed right so I am posting here.

    Thank you!
  2. Audioguru

    New Member

    Dec 20, 2007
    I answered your questions on another website.
  3. secrect


    Feb 1, 2009
    could you give the link of your another website?
  4. mbird

    Thread Starter Member

    Jan 29, 2009
  5. eblc1388

    Senior Member

    Nov 28, 2008
    I know how you feel. :)

    I once have a case where the OP ask the same question again on another website but with comments like "Some guys told me to use/do xxxx, what do you guys thinks".

    I nearly replied "That's rubbish, don't listen to a single word he said." :D

    Sorry to OP for hijacking the thread.
  6. mik3

    Senior Member

    Feb 4, 2008
    Use an op amp to amplify the voltage and then use a transistor in an emitter follower configuration to drive the speaker. The best solution, however, will be an audio amplifier. Have a look at for audio amplifiers integrated in a chip.