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Old 7th September 2010, 07:34 PM   #1
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Default TDA8920 stability problems w. boost circuit

Hello there.
I have bought this amplifier from ebay: TDA8920 Class D Amplifier board/ audio Power AMP 2X100W - eBay (item 120592625186 end time Oct-04-10 06:18:32 PDT)
It runs just fine on AC, but when I try to use DC from a LM2577 boost circuit I have made it just starts chopping (if you know what I mean). It runs 55VDC with the AC connected, and about 52-53VDC with the booster circuit.
I have some thoughts of, that it is because of high frequency noise from the output from the LM2577 that cause instability.
If so can I remove that noise somehow?
I would really like it to work with battery supply.

Thanks in advance,

Simon H.A.
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Old 11th September 2010, 05:19 PM   #2
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I tried to use this circuit without success.
40V 2A LM317 & TIP42 Power Supply
Any suggestion to the problem?


Simon H.A.
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Old 11th September 2010, 06:16 PM   #3
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Location: Midland, Michigan
Perhaps the battery supply can't produce enough current to power the amplifier.
Have you measured the voltage from the booster circuit while the amplifier is delivering power to the speakers? If the voltage is sagging, you probably need a battery supply which can deliver more current.
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Old 12th September 2010, 05:30 PM   #4
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The voltage on the output is swinging with about +/- 0.2 volt (40VDC). But I guess I need to charge my battery since it got low voltage. It swings from 11.1V to 11.5V. It is a 12 volt drill battery. Should be able to take the amps.
I will come with results after it has been charged.
I will also change the wires from the battery to the boost circuit, since it's just some thin alligator clip wires right now .


Simon H.A.
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Old 12th September 2010, 08:54 PM   #5
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Hmmm... no results from charging the battery.
I think I will make a DC to AC converter instead. Does anyone have a simple solution to this? Well I mean a ciruit that is not too advanced to build.
I will also be graceful for any suggestion to this problem. I have an oscilloscope so it is possible to make some measurements if needed.
But here is how it works when I power on:
  • A lot of noise from the LM2577 (I have a pretty large capacitor on the board, so I guess its normal?)
  • The amplifier starts playing just fine for 3-5 seconds
  • The amplifier starts clicking
The voltage output from the regulator doesn't swing so much. About +/- 1 volt max.


Simon H.A.
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Old 15th September 2010, 09:25 AM   #6
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I'm thinking of synchronizing. Lets say the amp runs at 300khz. The smps can be divided from that number, can be 150khz, 75khz, 37.5khz. If both are synchronized (the clock came from 1 same clock with divider), usually the whole thing works better.
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Old 15th September 2010, 08:01 PM   #7
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My booster has an internal frequency of 52 KHz, so I will have to set the frequency of the amplifier to 416 KHz.
My problem now is, that I can't seem to find any formulars on how to calculate the frequency for the amp. They only say you will get 345KHz when using a 30 KOhm resistor.


Simon H.A.
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