What is this additional capacitor added to PAM8403 Audio Amplifier Board for?

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#31
PRR said:
Any efficient audio Power amp needs a power storage reservoir. If it is "close" to the AC power supply that unit's filter cap can do the job. If there are long wires between, it is conventional to put some local storage "AT" the power amp.

> I can find nothing on the web to confirm

Try the spec-sheet. https://www.diodes.com/assets/Datasheets/PAM8403.pdf
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Hi, I am resurrecting this quite old thread to make a newbie question: how do you know that pin4 and pin13 indicated on the datasheet correspond to C7 (or C8) on the board?

Thank you
 
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#32
francescoboc said:
Hi, I am resurrecting this quite old thread to make a newbie question: how do you know that pin4 and pin13 indicated on the datasheet correspond to C7 (or C8) on the board?

Thank you
Click to expand...

Hi francesco
If i understand you correctly:
the only way to check is the layout on the pcb if this is according to the datasheets recommendation. "reverse engineering" 😉


The power reserve are stored in the caps (decoupling caps) - the caps should be mounted as closed to the power pins as possible. the size e.e.g 470µF is for a 2W amp suficcient in my view.
chris
 
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#33
The purpose of decoupling caps is to stiffen up the supply voltage at AC, so they aren't modulated by the load current so much. This compensates for stray resistance and particularly inductance in the supply wiring. Stiffening means lowering the AC impedance.



The smaller the cap value the closer it should be to the chip as its handling higher frequencies. Electrolytics don't need to be particularly close, ceramics with values around 1 to 100nF should be right on the pins of the chip, within a few mm.
 
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