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Class D amplifier - Power issue?

Discussion in 'General Electronics Discussion' started by gibon0695, Feb 7, 2016.

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  1. gibon0695

    gibon0695

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    3
    Dec 2, 2015
    Hello. I've built a class D amp. I need some help.

    Have a look at my video here:


    As you can see, amplifier works perfectly to about 75% volume. When I take the volume past this point the speaker output starts to 'chop'.

    When I connect just one speaker this problem does not occur, I'm able to turn the volume all the way up and it is LOUD.

    However, with two speakers, obviously requiring more current, it doesn't seem to reach full volume without chopping.

    The battery I am using is 12V rated at 1-2.4A output current.

    The chip is a TI TPA3122: http://www.ti.com/lit/ds/symlink/tpa3122d2.pdf

    Speakers are 10W RMS 8 Ohm.

    Gain is set at 20dB.

    I've checked the data sheet and this battery should be more than enough to power both speakers. Is it possible that the cheap Chinese battery isn't delivering the current it says it can deliver?

    Any feedback/help would be greatly appreciated, thank you!

    EDIT: These will be useful:
    [​IMG]
    [​IMG]
     
    Last edited: Feb 7, 2016
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Hello
    The first thing I would is measure the battery voltage when it's not doing it and when it is. This will tell you if the battery is dropping below the working voltage of the device. Also have a look at the maximum input voltage of the device, you may be over driving the input.
    Thanks
    Adam
     
  3. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
    Thanks for the reply.

    The battery voltage is 11.6V at the moment, (it is slightly discharged).

    The data sheet states that the amplifier operates between 10-30V...

    I don't think I'm over driving it as there is no problem when powering just a single speaker.
     
  4. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    What does the battery voltage drop to when its doing it?
    Adam
     
  5. cjdelphi

    cjdelphi

    1,096
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    Oct 26, 2011
    I tend to agree with you, sounds like a lack of available current from the battery...

    Better battery time?
     
  6. gibon0695

    gibon0695

    27
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    Dec 2, 2015
    I've just measured it at the point where it works and then when it starts chopping. The battery voltage does not move. Constant 11.6V...
     
  7. gibon0695

    gibon0695

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    3
    Dec 2, 2015
    Yeah it has to be! I don't have a variable power supply at home so it sucks that I can't hook it up to be sure
     
  8. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    If the battery voltage stays the same then it's not a current issue, it must be something else otherwise the battery voltage would drop.
    Adam
     
  9. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    The device will most likely have an over current limit circuit, maybe you are asking it to deliver too much current into the speakers?
    Adam
     
  10. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
    I thought about this. But, I don't think that is the issue, simply because the speaker is much louder when I connect just one of them at a time. That means the speaker can handle the current. This chip is capable of delivering 15W per channel when connected to a 28V supply, I am only aiming for around 3W per channel with my speakers. The speakers can actually driver up to 10W RMS (15W peak).

    P= V * I
    = 12V * 0.25A
    = 3W Per channel (6W Total for 2 speakers)

    Total current draw for both channels should be a max of 0.5A at 12V (According to the graphs in the data-sheet).

    I can't see how there's a power or current issue... but there certainly is one somewhere!

    If the battery is supplying 1A like it says it does, there should be more than enough current? right?
     
  11. Alec_t

    Alec_t

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    813
    Jul 7, 2015
    Battery labels are more likely to specify the Ampere-hour (Ah) capacity than the maximum current they can provide. Can you post a link to the battery spec?
     
  12. gibon0695

    gibon0695

    27
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    Dec 2, 2015
  13. Alec_t

    Alec_t

    3,004
    813
    Jul 7, 2015
    I can't see anything on the battery label to indicate the battery output current capability. Where did you see the '1-2.4A output current' info? On the charger?
     
  14. Arouse1973

    Arouse1973 Adam

    5,164
    1,087
    Dec 18, 2013
    Maybe its because you have built the design using varo PCB? Those skinny tracks might be the issue. Measure some of the voltages around the circuit?
    Adam
     
  15. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
    It says in the description of the product on ebay:
    "Output voltage: 10.8~12.6 DC"
    "Output current: 1-2.4A"
     
  16. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
    Possibly, but I had the exact same issue on breadboard, I built it on vero board to see if that changed anything... I will continue to test it, going to hook it up to a power supply when I can
     
  17. davenn

    davenn Moderator

    13,901
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    Sep 5, 2009
    please give an ebay link
     
  18. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
  19. davenn

    davenn Moderator

    13,901
    1,971
    Sep 5, 2009
    sorry, missed that

    the battery is rated at 4800mAh

    cant quite read the label on the plugpack ... 12V at some unknown mA rating

    it was that bit you got wrong ;)


    Dave
     
  20. gibon0695

    gibon0695

    27
    3
    Dec 2, 2015
    Just checked the plug!!

    "Output: 12.6V DC - 500mA"

    Thank you. Lesson learned. Don't trust eBay. Now makes sense why it wouldn't fully power both drivers...

    I'm going to hook it up to a Power Supply tomorrow and see what happens, I'll let you know...

    I still need a battery though, as this amplifier needs to be portable!

    Do you know any good places I get a pretty cheap 12V rechargeable that is capable of supplying 1-2A?
     
    davenn likes this.
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