A (simple) question about PSU

[billy]

I have found this schematic of a dual +-12v psu and  I have a question about capacitors :

I am aware that the two big 2200uF capacitors are for smoothing the transformer output and the two 10uF for providing a stable output from the regulators. But why are so many 100nF capacitors in parallel ? High frequency filter ? But why not one but so many ?

[MP]

Yes, these are for high frequency filtering. It is hard to find a 0.6 microfarad or 0.7 microfarad capacitor, which is what this makes up. Also, some designers like to parallel capacitors because each capacitor charges to the same voltage, without regard to the behavior of the other capacitor. Personally, I have never built a circuit that was critical enough to require this.

MP

[KevinIV]

I have a question. If you have a simple LC filter with the output taken across the capacitor, does the load current and voltage depend on the fact that maximum power occurs when the source voltage is in phase with the current. This would mean the inductive reactance should equal the capacitive reactance.

[MP]

First, I will have to assume you are talking about a power supply with AC output, since such a filter will do nothing with DC.
Secondly, the frequency and phase of the circuit really are not relative to the voltage since they are related to the timing and lag of the signal whereas the voltage is the amplitude. Any passive filtering will take away from the amplitude somewhat, but this is simply loss in the circuit and not a characteristic of the LC configuration.
But, perhaps I have misunderstood what you are asking.

MP
 

[KevinIV]

I think I follow. But you have to admit that although the inductive reactance is greater than the capacitive reactance for good ripple reduction, the idea of equal reactance is tempting. Maximum power is transfered to the circuit when the peak voltage is in phase with peak current.