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Old 27th July 2008, 02:46 PM   #1
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Default Class D - about current consumption from the supply - a question folks

When operating, class D switches the supply voltage and the heat is small...because on and off and using fets...but about the curent flowing from the supply without speaker connected?

Is the current consumption, from the supply, drained in a constant way WITH and WITHOUT load (speaker) connected?

I have suspections that not.... but i have doubts, and some folks asked me that and i do not know what to answer.

In my imagination you need to insert the speaker to have big current consumption...but i may be wrong...very confused i am in this moment about this subject.

Can you help me folks, to help brazilian folks about that?


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Old 27th July 2008, 04:08 PM   #2
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Power supply current will be very low with no speaker load.
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Old 27th July 2008, 06:15 PM   #3
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Hello Carlos

The current consumption in class-d amps is not more than 100mA in typical setups.

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Old 27th July 2008, 07:33 PM   #4
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It's been a while since I last posted, but I couldn't resist this thread.

Theoretically speaking, an ideal switched mode amplifier would consume no power internally - its average input power draw would be exactly equal that provided to the load (so no load - no power draw).

In actuality, there will always be some small amount of housekeeping power (typically a few watts) and some output f C V squared losses and possibly some shoot through losses if near zero dead time timing is used in an effort to minimize distortion. - a.s.

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Old 28th July 2008, 08:26 AM   #5
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I've found that on self-oscillating amps designed for PA applications (using fairly long dead times - distortion only has to stay below 1%), then the dominant cause of the idle current in the output stage is the ferrite losses in the output filter. Even with no load, you're still magnetising the output filter chokes in one direction, then the other direction at perhaps 300kHz. Moving to the Ferroxcube 'Polo Mint' gapped ferrite toroids, I see a useful reduction in idle current.
Certainly in 'ucd' style amps, the quiescent current tends to drop when a load is connected to the amp. (With no input signal obviously).
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Old 28th July 2008, 08:48 PM   #6
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I agree, there seems to be very little difference in idle current with andwithout loads in the amps I've measured.

But I've measured low power amps, so YMMV.
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Old 18th August 2008, 02:57 PM   #7
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Default Thank you folks... and hello my dear Workhorse

Now my doubts do not exist anymore...thank you all.

Sorry by the enormous delay to answer you all....thanks.


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