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    Class D amp output current

    Hi all,

    I have a question and a few concerns. I currently building a class amplifier for bass frequencies. the switching frequency is 30 kHz. My problem is that I am testing my amplifier on a breadboard which is rated at 1A. The Mosfets rail voltage is 28v and I need a output current of 7A for a output power of 200W for a 4 ohm load. I am scared of testing the power stage on the breadboard because of the high current. Is there anyway I can test the power stage on breadboard? Can I use a perfboard?

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    Re: Class D amp output current

    Three problems!
    1. even at 30KHz you need to keep wiring lengths and coupling between connections as low as possible so any 'patch matrix' prototype board is really unsuitable.
    2. Yes, the current will cause you problems.
    3. Although class D is efficient, the output devices in particular will still run quite hot, can your breadboard or perfboard withstand the heat and have space to accommodate heat sinks?

    Brian.
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    Re: Class D amp output current

    Yes, the breadboard and perfboard have space for the heat sink but can the breadboard gets be done with such high currents? I am looking for a way to test the MOSFETs section, I already got the driver to output a signal.
    Also, I have external deadtime will there still be heating problems?



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    Re: Class D amp output current

    Hi,

    Read the datasheet.
    Especially layout considerations, design considerations.
    Read application notes.

    Usually a breadboard can not fulfill the requirements. If so, a breadboard simply is not suitable.
    No need to waste time with it. One can not gain useful informations.

    Generally a breadboard is not suitable for
    * high current applications
    * high frequency applications
    ....
    A class D amplifier combines both.

    Klaus
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    Re: Class D amp output current

    The RMS current is 7A but the current peaks will be 9.9A. A breadboard might be destroyed with only 1A.
    A breadboard's rows of contacts and long wires all over the place are antennas that pickup interference and hum in audio circuits. The capacitance between them causes an amplifier to oscillate.
    Use a breadboard for DC low current LEDs to turn on and turn off.



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    Re: Class D amp output current

    Do it dead bug style with in-the-air wiring except for gnd connections and power on a suitable 1oz or 2oz solid plane copper FR4 and use wide traces if you put all power pins on the board. Not sure but maybe perfboard pads may peel off or burn if they get very hot. Lots of pcb design and prototyping resources explain how to calculate track width for x Amps and mm2 for (some) heatsinking. Apart, they should abolish the archaic 'mil' measurement, everything is metric.


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    Re: Class D amp output current

    Thank you all for your replies but if I decide to keep the current under 1A using a bench power supply HY3002-3, will this be a way to test my circuit?



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    Re: Class D amp output current

    Hi,

    Did you read the datasheet? What does it say? It tells you all you need to know.
    If you want me to give an answer, I need to read the datasheet, too.

    Did you read the posts before?
    Why do you think a 1A power supply can remove the high frequency thing of the class D amplifier?

    Klaus
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    Re: Class D amp output current

    Quote Originally Posted by jbec View Post
    current under 1A using a bench power supply
    Start with low volts from the power supply. Your circuit draws less power.
    Watch for misbehavior as you gradually increase supply volts. Touch components that tend to overheat as power consumption rises.

    If something starts to go wrong then reduce supply voltage. Watch whether operation goes back to normal or whether the condition locks up.


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    Re: Class D amp output current

    Just a word of caution as we have not seen the schematics for this amplifier - class D MOSFET amplifiers usually run the devices in hard ON or hard OFF states to achieve efficiency. If you reduce the supply voltage there is a risk of the gate drive voltages being insufficient to fully switch them and they may start to work in their 'linear' region. If that happens the current consumption could increase and with a small bench supply cause all kinds of problems, most likely some kind of cyclical start and stop oscillation.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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