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I'm working with an audio board (company project) that is powered by a external 9V power supply. Actually an ordinary AC adapter, like this one: http://www.sweetwater.com/store/detail/MAud9v500. The power supply project of our board seems to me kind of an overkill. I say that because of this lot of capacitors, also I not sure about the inductors. Are they really doing any work there? Since the external power supply is - supposed to be - linear, I guess all those capacitors are necessary.

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Apart that, those caps are taking extra money and extra space in PCB board.

What do you think?

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  • \$\begingroup\$ More to the point, if the current levels on your schematic are even close to accurate, and the linked adapter is close to what you're using, the adapter is badly underpowered. \$\endgroup\$ – WhatRoughBeast Jan 24 '15 at 19:31
  • \$\begingroup\$ @WhatRoughBeast, the linked adapter is only an example. The used power adapter can supply until 2A. \$\endgroup\$ – Ricardo Crudo Jan 24 '15 at 19:37
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Let's say the load of the AUDIO POWER is around 4 ohms. And the requirement is to have the power rail changes no more than 5% with 100% changing 4 ohm load, therefore the power supply impedance needs to be less then 4 ohm x 5% = 0.2 ohm.

Further assume that the power supply is an unknown cannot be relied on and the 0.2 ohm impedance is to be satisfied with on-board capacitors only at 40Hz (lowest audio frequency desired).

C = 1 / (2 * pi * freq * 0.2) = 0.02 F = 20000 uF (I could be off by a factor of 2)

So at first glance, the capacitors seem way overkill, but there are conditions where they can be justified. It really depends on the load, the power supply and the requirements.

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