Help with AC Amplifier

Discussion in 'The Projects Forum' started by Raymonde, Feb 6, 2013.

  1. Raymonde

    Thread Starter New Member

    May 5, 2010
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    Although I have some knowledge of digital logic, analog circuits are a bit of a mystery so I need help please. We have a digital phone system where the base ringer activates a small 8 ohm speaker using 1.8v AC. I want to light a couple of LEDs (red) when the speaker activates (without any other connections to the phone except to the speaker) so I'm thinking a simple emitter follower amplifier to get sufficient voltage to drive the LEDs. The LEDs would be about 6 feet from the phone and could house a 9v battery for the amp power source. Is an emitter follower a reasonable approach?
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    An emitter-follower LOSES voltage but it increases current, it does not increase voltage.
    A common-emitter transistor with the load from its collector to the positive supply (for an NPN transistor) amplifies voltage and also amplifies current.
    The transistor will need a resistor in series with its base and the LED will need a series resistor. The resistors limit the current.
     
  3. Raymonde

    Thread Starter New Member

    May 5, 2010
    2
    0
    Thank you. I did some additional reading based on your comments and I now think I'm on the right track..
     
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