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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th December 2007, 05:12 PM   #41
djQUAN is offline djQUAN  Philippines
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time for a rebuild....

plans for a new chassis layout, new SMPS and preamp boards.

following eva's advice and to try out something new, I decided to incorporate 18V gate drive to the SMPS fets.

a few things about the supply....
-board width same as amp8 pcb lenght
-has thermal and input overvoltage protection
-18V gate drive for the switching fets for lower switching losses
-lots of input and output capacitance (if I can get caps to fit in the layout)
-direct to board power input connections (basically, power wires go straight to the board. no on-board connectors)
-already includes the +5V and +/-15V supplies for the chipset and preamp circuitry
-single layer board!!!! I didn't want to spend extra cash for new blank boards and going single layer made etching easier. took about 49 jumpers in all. many are paralleled as they carry high current. high current tracks in confined areas have 15ga copper wire soldered to the tracks for more current capacity.

here are a couple of pics of the power input terminal blocks from 3/4" square brass bars that I made using a drill press, taps and a grinder.

front and top view:
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bottom and rear view:
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and here's a photo of the partially populated board and how the terminal will be put to use.

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Old 2nd January 2008, 01:50 PM   #42
djQUAN is offline djQUAN  Philippines
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a preview of things to come......

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Old 4th January 2008, 05:00 PM   #43
Gyula is offline Gyula  Hungary
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djQUAN! YOU ARE THE KING! CONGRATULATIONS!
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Old 4th January 2008, 06:39 PM   #44
Eva is offline Eva  Spain
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Isn't this power supply a bit overkill? I think that you could do with half that, or at least in half that size. Single sided boards are easier and cheaper to make, but this comes at the expense of extra EMI and space used. That's why I designed such a tiny push-pull SMPS for my car amp, and it worked fine for 2x150W class D despite the size. You are doing a great job anyway
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Old 5th January 2008, 05:06 PM   #45
djQUAN is offline djQUAN  Philippines
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Eva,

well, this would be used for sub duty and I'm expecting to drive this into clipping and will be playing bass heavy music (yeah I know, you guys hate boom setups. but this system will be designed for good SQ but have bone crushing bass when called upon. ) besides, since I'm already building my own amp, why not over-engineer?

I haven't had issues regarding EMI with the first SMPS and that was with a metal case and an acrylic top. this one will be in an all alu case. hope that helps reduce EMI.

I don't have the right component (zener) in my parts bin to provide 18V gate drive but with the components right now, I have regulated 15V gate drive right at the fet gates. do you think that is enough or will 18V have better performance compared to 15V?


some updates:

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Old 6th January 2008, 08:46 AM   #46
luka is offline luka  Slovenia
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Hi

Don't tell me that fets on amp are STW34n20, how can TK2350 drive 8 of them?
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Old 6th January 2008, 03:10 PM   #47
djQUAN is offline djQUAN  Philippines
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yes, they are STW34NB20.

the tripath datasheet says that two pairs per side of those fets are the maximum that the chipset could drive.

the driver chip gets so hot that although the chip itself is soldered to the PCB and a heatsink is not enough. it still needs a bit of fan cooling.
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Old 6th January 2008, 04:26 PM   #48
djQUAN is offline djQUAN  Philippines
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here's the fet:

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was busy with other things so not much was done. I just rewound the toroids and made little mounts for them.

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I don't want to mount the coils off-board but they won't fit the casing when board mounted and the vibration will break the wires off so I have to mount them to the chassis.
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Old 6th January 2008, 04:38 PM   #49
BWRX is offline BWRX  United States
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Where do you plan on mounting them off board? You really want to keep the switching node between the FETs and the inductor as short as possible. Is it possible to mount them at a 45 degree angle to the PCB to give you some more clearance?
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Old 6th January 2008, 04:45 PM   #50
djQUAN is offline djQUAN  Philippines
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I will be mounting them horizontally above the fets. I will try to keep the wires from the half bridge to the inductors as short as possible.
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