Hello,
I'm building audio project around the couple STA311 PWM controller and STA516 power stage.
This couple is interesting for us at it allows to have a variation of our electronic to drive 8 vibration transducer in a specific product. Otherwise we would run a 80-90W 8R audio amplifier (on mono or 2x45W stereo)
Our projects will run on PoE power, so the STA516 is interesting as its max power supply is at 60V. Our PoE stage will provide 50-57V maximum. So it should avoid us to include a buck of flyback stage.
Anyway the problem now during the trials of our prototypes is that our amplifier board is consumming to much power for even low audio signals.
Before injecting 55V from PoE, I'm trying with smaller voltage.
And with 16V supply we have already 2,7W consumption (30V - 9W). Would reach a crazy 20W at 52V? On only one regular speaker 8ohms.
These 2,7W is the minimum as soon as a signal is present on digital inputs.
I suspect something wrong maybe on the STA311 configuration making generating PWM signals making amplifier working a lot outside the audio band.
Or maybe there is something wrong with the output filter components. They are the ones coming hot, power is not taken by the speaker.
Nothing fancy about them as they are chose from the ST Datasheet.
Have you any suggestion?
Thank you.
I'm building audio project around the couple STA311 PWM controller and STA516 power stage.
This couple is interesting for us at it allows to have a variation of our electronic to drive 8 vibration transducer in a specific product. Otherwise we would run a 80-90W 8R audio amplifier (on mono or 2x45W stereo)
Our projects will run on PoE power, so the STA516 is interesting as its max power supply is at 60V. Our PoE stage will provide 50-57V maximum. So it should avoid us to include a buck of flyback stage.
Anyway the problem now during the trials of our prototypes is that our amplifier board is consumming to much power for even low audio signals.
Before injecting 55V from PoE, I'm trying with smaller voltage.
And with 16V supply we have already 2,7W consumption (30V - 9W). Would reach a crazy 20W at 52V? On only one regular speaker 8ohms.
These 2,7W is the minimum as soon as a signal is present on digital inputs.
I suspect something wrong maybe on the STA311 configuration making generating PWM signals making amplifier working a lot outside the audio band.
Or maybe there is something wrong with the output filter components. They are the ones coming hot, power is not taken by the speaker.
Nothing fancy about them as they are chose from the ST Datasheet.
Have you any suggestion?
Thank you.
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The hot inductors may show the elephant in the room. I suspect your system outputs permanent 50%pwm in idle state.
This results in significant circulating output current in standby mode even without any audio signal.
There are more sophisticated modulation schemes that reduce standby power, you may have a look at some TI appnotes.
On the other hand losses may be reduced using better (i.e. bigger) output inductors.
And yes, there are only few class-d-chips suitable for PoE-voltages.
This results in significant circulating output current in standby mode even without any audio signal.
There are more sophisticated modulation schemes that reduce standby power, you may have a look at some TI appnotes.
On the other hand losses may be reduced using better (i.e. bigger) output inductors.
And yes, there are only few class-d-chips suitable for PoE-voltages.
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Just measure the duty cycle of the unfiltered output signal of the power-stage with no audio input signal.
The data sheet does not specify any power saving features - so it looks that my assumption is true.
To reduce standby losses another modulator may be helpful - if there is any available.
Anyway, the output filter is crucial for standby losses.
Use low loss inductors (=bulky).
It may also help to increase inductance for a certain amount thus reducing circulating currents.
Personnally I never liked STM class-d-chips that much for their high losses and preferred TI.
The data sheet does not specify any power saving features - so it looks that my assumption is true.
To reduce standby losses another modulator may be helpful - if there is any available.
Anyway, the output filter is crucial for standby losses.
Use low loss inductors (=bulky).
It may also help to increase inductance for a certain amount thus reducing circulating currents.
Personnally I never liked STM class-d-chips that much for their high losses and preferred TI.
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