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Thread: 1200W Class D Sub-woofer Amp. Help Needed

  1. #1

    1200W Class D Sub-woofer Amp. Help Needed

    I have been spending way to much time reverse engineering this sub-woofer class-d amp and need help. Power Supply rails are are designed to be +/- 165 VDC. As I slowly increase the AC main supply voltage, the DC supply voltage increase steadily until I reach about +/100 VDC, with minimal AC current draw. When I surpass +/-100 VDC a 10 A inline AC fuse blows. The DC voltage distribution/regulation measures okay. The six (6) IRFP450 MOSFET appear okay by checking them out of circuit using an ohm meter. The four (4) 1st stage MOSFETs use a single IR2113S high and low side driver, the two last stage MOSFETs use two (2) IR2101S separate low and high side drivers. The schematic is attached to this post (sorry upload utility is not working). After hours of following circuit traces and trying to understand the circuit, I am about to admit defeat. I am posting this in a last and final effort in the hope that other may have have a similar experience. Thanks,-Ed

  2. #2
    Quote Originally Posted by EMarks View Post
    I have been spending way to much time reverse engineering this sub-woofer class-d amp and need help. Power Supply rails are are designed to be +/- 165 VDC. As I slowly increase the AC main supply voltage, the DC supply voltage increase steadily until I reach about +/100 VDC, with minimal AC current draw. When I surpass +/-100 VDC a 10 A inline AC fuse blows. The DC voltage distribution/regulation measures okay. The six (6) IRFP450 MOSFET appear okay by checking them out of circuit using an ohm meter. The four (4) 1st stage MOSFETs use a single IR2113S high and low side driver, the two last stage MOSFETs use two (2) IR2101S separate low and high side drivers. The schematic is attached to this post (sorry upload utility is not working). After hours of following circuit traces and trying to understand the circuit, I am about to admit defeat. I am posting this in a last and final effort in the hope that other may have have a similar experience. Thanks,-Ed
    Trying to help you out with no schematic here. I don not know what kind of driver you have maybe an irs2092 or something similar.

    1) check out the dead time as you may have a case of shoot trough.
    2) Check also that you are giving the supply voltage in the right place and not in the 110v supply input.
    3) check the voltages at the mosfet drivers and see that both high and low side drivers have the supposed drive voltage at their input, see that the voltage is maintained and not falling for any reason.
    4) Check for any dry joints, any inductors that may have there coil cut with vibration.
    5) Check your input and output capacitors, they may have gone bad.
    6) If any bootstrap capacitors are used change them and see that you fit good quality ones.
    7) Check if the auxiliary supply is working correctly and check for any faulty capacitors in that area. Do not forget the start up circuit cannot withstand the load for more than a few cycles. If possible disconnect the amplifier circuit and try the smps alone.

    Finally use a 100w lamp in series with your supply rail for protection. This will show you better if the fault still persist.

    Lastly when posting files see that they are in pdf form and use the GO Advance from the bottom task bar. Use the paper clip icon on the top task bar to attach the schematic file.

    Good luck Regards, Silvio.
    Last edited by Silvio; 09-04-2020 at 10:08 AM.

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