What's with the small and large caps at input/output of regulator?

Question

Look at this website. http://www.electronics-lab.com/projects/power/015/index.html Now I'm wondering why have the large and small caps at the input and output of the regulator. I understand that the caps help stabilize the voltage at the regulator, to keep it from oscillating, but why have a relative large and a relatively low capacitance? Since capacitors in parallel add, the outputs of the regulators essentially have 101uF of capacitance. Why not just put a 200uF cap there and call it a day? Same with the input to the regulator. There's a 2200uF in parallel with a 1uF, oooooo, 2201uF!! Why not just put a 3000uF there if you want more than 2200uF?

Answer 1

Large capacitors have a poor high frequency response. The small capacitor has a much better high frequency response. To get the complete picture you would need to know the resonant frequency of each capacitor. That is the frequency at which the inductance and capacitance have equal reactances within each capacitor. A large capacitor may have a resonant frequency of 10kHz to 100kHz and the smaller capacitor may go from 1MHz to 10MHz. So the small capacitor extends the capacative effect to a much higher frequency then just the large one alone.