Capacitors and current limits

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You can think about it in terms of charge Q.
Q = integral of I with t
(If I is constant it’s simply Q=It )

The charge the amp draws from the caps has to be refilled by the transformer and rectifiers. The faster that charge is replenished the higher the current required.

Very short recharge time will demand very high current. Say your amp demands 1A on average while playing music loudly, and the recharge time is one-tenth of a recharge interval, the average recharge current would be 10A.

The diodes have to handle the high recharge current and so does the transformer. Transformers also have series “leakage” inductance and some winding resistance. Too much current can saturate the core and hugely increase the leakage inductance. This is why you see some audio amps using transformers whose power rating seems much bigger than their output power alone would justify.
 
hi guys i need some more advice. the controller datasheet says: "Where the regulator is powered from a source with high AC impedance, a 0.1 µF capacitor connected between Input and GND is recommended. This capacitor should have good characteristics to above 250 kHz."
What is "a source with high AC impedance"? do i need this capacitor?
Thank you so much.
 
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A new 9 volt battery and a used 9 volt battery is one example of a low and a high impedance voltage source. Both read about 9 volts off load but the used one has two issues, it can not supply much current without the voltage sagging and that 'high' impedance means interference can be impressed upon it.

Take a 'perfect' low impedance voltage source and connect it via a meter of wire to a circuit and the inductance of the wire has made that far end of cable 'high' impedance as far as picking up high frequency interference is concerned.

So we slap a small cap across the connection to add a defined low impedance path that will 'short out' or 'shunt' the high frequency interference it may pick up. A small film type cap is needed because large electrolytics have worsening performance as the frequency rises.
 
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Yes, you need the cap to 'force' a low impedance. That really means the circuit will work correctly no matter what the impedance may be in front of it... which is really an unknown as it is circuit and wiring/layout specific.

So we add the cap and the problem goes away. It can never do any harm.
 

PRR

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> on the input and ground of the regulator as datasheet says?

Yes, of course.

Unless there is a capacitor "near by", like a few inches.

I used to solder the regulator right on the 1,000uFd main filter capacitor, then very short leads to 1,000uFd on the amplifier board. Then there is no need for little caps "at" the regulator. But when in doubt, use them. Not expensive.
 
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sorry I take advantage of your kindness. Does this 0.1uF capacitor have to be physically close to the regulator or can I put it where I want?

It has to be where the circuit design needs a low impedance point to be.

So in simple terms the regulator chip needs the applied input voltage points to be low impedance and so that means the small cap has to be close to the actual regulator pins involved, the input and ground pins. Same for a small cap on the output.

If there is several cm of print or wire between the chip and the cap then the effect of the cap is reduced at the point it is needed.
 
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I'm just looking at the data sheet for the part you mention earlier... and I'm going to just revise what I said earlier.

So I would add the 1uF cap on the input side of the reg which will ensure low impedance at that point, and then follow the manufacturer recommendation of using an electrolytic at the output.
 

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