Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I've been looking at the LM78xx.
simulate this circuit – Schematic created using CircuitLab
The notes state:
So, input and output must be referenced to ground. C1 removes power line noise/ ripple and C0 improves switching stability.
Why was .33uF selected for the input capacitor and .1uF selected for the output capacitor?
Strongly related: Capacitor Sizes for 7805 Regulator
Anyway, these values are actually not critical, especially for these kind of regulators (linear regulators made out of a NPN transistor). Those can be made stable with almost any input/output capacitor values, or even no capacitors at all. Those values have been suggested in the datasheet because they provide a good compromise between cost/size and stability/noise immunity for a large range of output current. Just trust the guys that settled on those values.
Note that for LDO (low dropout) type of regulators, however, the capacitor values are more critical, because the stability of those regulators depend on the capacitor values (mainly the output capacitor). In this case, it is clearly indicated in the datasheet, sometimes with a graph indicating the stable region (with capacitance vs output current). In addition to the capacitor value, the capacitor ESR can also be relevant for LDO stability.
A link that provide informative data regarding capacitor roles in regulators (and for all kind of regulators): http://www.ti.com.cn/cn/lit/wp/snoa842/snoa842.pdf
