Hi, sorry for not responding, I have been out of town for a bit. Something I was recently wondering about the capacitors, was why at 60hz they need to be at 470nF. I tried looking this up, but I could not find anything.
The choice of reservoir capacitor depends on the ripple voltage that you can tolerate, according to the formula,
Q = C * V = I * T ...(F1)
Where,
Q = Charge stored by a capacitor in Coulombs (number of electrons)
C = Capacitor capacitance value in Farads
I = Current drain from capacitor in Amps
T = Time in seconds.
For example, you have a 60Hz power supply which has a full-wave rectifier (bridge) and a reservoir capacitor. You want to drain 1 Amp from the reservoir capacitor and you can tolerate a maximum ripple voltage of 2V peak to peak. And you would like to calculate the minimum value reservoir capacitor that you will need.
From formula 1 (F1) you get,
C = (I * T)/V ...(F2)
Where,
I = 1 Amp (the current drain from the reservoir capacitor)
T = 1/(60 * 2) = 0.0083 seconds ( for a full wave rectifier the reservoir capacitor gets charged back up to maximum voltage twice for very cycle of the supply sine wave)
V = 2 Volts (the allowable ripple voltage)
Thus,
C = (1 * 0.0083)/2 = 0.0045 Farads or 4,500 micro Farads (4,500uF)
There are other factors that affect the ripple voltage but, for a typical power supply, the above formulae will not be too far off.
spec