Filtering Capacitor Sizing for Voltage Regulator IC's

Thread Starter

wbhowarth

Joined Mar 9, 2021
3
Hello friends,

I am working on a circuit which utilizes a L78L33 voltage regulator. My inquiry is in regard to filtering capacitor selection.

The test circuits in the datasheet feature .33 uF and .1uF filtering capacitors on the input and output pins respectively. Is a .33uF cap overkill? This is a very large value, no?

Another note, to power my circuit I am already relying on a 12V AC adapter, the 3.3V from the IC is just to power a microcontroller. I assume the adapter already features filtering circuitry, so even if these large caps are appropriate for unfiltered power from mains, surely they are unnecessary with the IC voltage coming from a pre-filtered 12V, right?

Thanks and please forgive any glaring ignorance.
 

Thread Starter

wbhowarth

Joined Mar 9, 2021
3
Welcome to AAC!
Not necessarily. Sometimes they'll be significantly larger. It depends on input/output voltage differential, regulator, rectified voltage, rectifier type, output current, ...
Not safe to assume. Measure to be certain.
Thanks for the feedback Dennis. Suppose I measure the output of the adapter and find a clean 12V output, could I forgo the filtering capacitors on the IC?
 
Top