LM1875 worked ! But there is a problem

Discussion in 'Power Electronics' started by Mohamad Tarabah, Jan 8, 2017.

  1. Mohamad Tarabah

    Thread Starter Member

    Jul 4, 2016
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    0
    Hi all, thanks to everyone's help, especially administrators answers the opamp circuit work. Now the problem is it's not outputting 20w : I'm trying it on a 5w 4ohm woofer and also tried to power it with 24v using lead acid batteries, still same. Please note that the 1uF cap at Vin is replaced by a polarized capacitor. I'm thinking of removing the 2200uF cap at out. What do you think ?
     
  2. bertus

    Administrator

    Apr 5, 2008
    18,509
    3,569
    Hello,

    The 24 volts is way to low for 20 Watts.
    At 24 volts you might expect about 5 Watts, as you are using single supply.
    The 2200 μF capacitor is a must for a single supply amplfier.
    Without it the speaker will have a high DC of about 1/2 the supply voltage.

    Bertus
     
  3. Mohamad Tarabah

    Thread Starter Member

    Jul 4, 2016
    54
    0
    So you mean this is normal. Ok so I should be using a 50v transformer in that case. Thank you
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    6,393
    1,485
    From the datasheet:
    upload_2017-1-8_17-26-5.png

    Using a single supply that means 50V or 60V.
    Note that the capacitors have to be rated to handle these voltages.
    You will get about 1.4 times the transformer voltage after the rectifier (assuming a full wave bridge) and smoothing capacitors so the transformer should be 35V to 42V.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    9,634
    1,109
    Is it designed to handle 50V Vcc?

    {ed}
    So it seems it can handle 50V.
    Beware if you are using 4Ω Speaker.
     
  6. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    6,393
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    The IC is and the circuit will handle such voltages if the capacitors are suitably rated.
     
  7. crutschow

    Expert

    Mar 14, 2008
    19,821
    5,544
    If you want more power from a 24V supply then you would need to use an audio amp with bridge type output, as that doubles the voltage across the speaker load for a given supply voltage.
     
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