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Old 14th August 2010, 02:41 PM   #331
Baldin is offline Baldin  Denmark
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Default Works but ....

Ok. Changed a few components, and skipped the big capacitor in the input ...

Now it starts up every time, but only with a load (speaker or 8 ohm resistor).
Switching freq is 235 kHz

Because I had to remove the big cap ther is 0,6 V DC on the output .... need to find a solution ... any suggestions??

Also need ot find a way to make it start without the load ...

Otherwise it seems quite good for a breadboard circuit

And I think it is an improvement over the original ........
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Old 14th August 2010, 03:48 PM   #332
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Its ALIVE!!!
YouTube - Homemade class d amplifier
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Old 14th August 2010, 05:48 PM   #333
Baldin is offline Baldin  Denmark
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Quote:
Originally Posted by Tekko View Post
Super

So, what was wrong?
Does it start every time?
....... also without load?

What is the switching freq?
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Old 14th August 2010, 05:56 PM   #334
lycanlk is offline lycanlk  Sri Lanka
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Quote:
Originally Posted by Tekko View Post
congratulations !
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Old 14th August 2010, 05:57 PM   #335
luka is offline luka  Slovenia
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x2

Tell me something OT, how did you get TI class d eval board and how much was it?
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Old 14th August 2010, 06:04 PM   #336
lycanlk is offline lycanlk  Sri Lanka
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Baldin,

Mine start smoothly with or without any load ! Sorry I cant help you technically.. I'm a guy building amps with very few of tools. but I think you have to improve the input stage with LM319 and try feedback resister 22k instead of 47k.

regards,
Lycanlk
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Old 14th August 2010, 08:19 PM   #337
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It started no prollem with or without load but its unfortunately dead again, a loose strand on the +15V feed wire to the IR2010 touched a transistor leg with caused severe farting and banging from the speaker, then it was dead.

I now fear that pretty much every semiconductor on the board is dead so i figure its easier to just make a new board and start over.

Oh well **** happens i guess.

Btw my switching frequency was around 7µS which is around what, 50-100kHz ?
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Old 14th August 2010, 08:50 PM   #338
81bas is offline 81bas  Germany
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Quote:
Originally Posted by Baldin View Post
Also need ot find a way to make it start without the load ...
The problem with the startup in selfoscillating class d amp usually is that it MUST start with the negative impulse at the output, to let the bootstrap capacitor charge (I mean the bootstrap capacitor of the mosfet driver). If this condition is not met (if the comparator waits for INITIAL positive impulse at the output), then the bootstrap capacitor is not charged yet, and it is not possible to open the high side mosfet and it is not possible to generate any positive voltage at the amp output. So the amp simply will not start to oscillate...

To solve this problem, it is usually enough to connect amp output to the positive voltage rail using 50K-100K resistor. This will generate small positive voltage offset at the amp output after power is on, and the input comparator will initiate the negative cycle first, which will charge driver's bootstrap capacitor effectively...
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Old 14th August 2010, 10:43 PM   #339
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The amp is back from the dead!!
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Old 14th August 2010, 11:58 PM   #340
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Heres a scope shot of the carrier resudial:
Click the image to open in full size.
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