I have made a full wave rectifier circuit to obtain 5VDC, 9VDC and -9VDC. To prevent the ripple, i have selected C1 and C2 as 4uF which were shown below. I will use a 12V, 6W transformer to get AC input signals. Do you have a suggestion related to values of these capacitors to avoid the ripple or should i choose bigger capacitances like 100uF? Boxes are 7809, 7909 and 7805 regulators. Thank you so much.
A bigger value is preferable, 4uF is when you have a decent DC into the regulator, 100 - 1000uF in parallel with a 100nF for higher frequency decoupling. a 100nF is needed on the output side as well.
Ref.: http://www.electronicshub.org/understanding-7805-ic-voltage-regulator/
Precise anwer comes from examining the charge stored in a capacitor
$$ Q = C * V $$
Take the derivative of that, with respect to small steps in time, and we see
$$ dQ/dT = C * dV/dT + V * dC/dT $$
Now assume the capacitor is constant (this is your filter capacitor), and replace dQ/dT with "I" (current) to find
$$ I = C * dV/dT $$
Rearrange this, to have dV (ripple voltage) on the left, thus
$$ dV = I * dT / C $$
Now let dT be 8 milliseconds (1/120 Hertz), I be one amp, and C be 10,000uF
You have dV (ripple) = 1 amp * 0.008 / 10,000uF = 0.008 / 0.01
or 0.8 volts ripple. At 1 amp, 10,000uF.
