| ??? 11/26/11 16:05 Modified: 11/26/11 16:09 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#184909 - There's no need for HF-ripple rejection... Responding to: ???'s previous message |
Erik said:
If you took the time to read it all - an not out of hand rejecting the article - you will see that, in fact, a switcher can be better than a linear in suppressing the noise from the preceeding switcher. A linear has virtually no suppression at the frequencies of the ripple from a switcher. In a two stage regulator concept there's usually enough headroom to add a simple low pass filter between the two regulators to eliminate the ripple of the preceeding switcher. There's no need to use a regulator providing high HF-ripple rejection at all. So, a good approach is to use a switcher, a low pass filter and finally a linear regulator. We do so since many years in using the LM2674 + LM7815 combination. If you use two switchers in a row, on the other hand, the second switcher might suppress the ripple of first switcher, but you still have the ripple of the second switcher!! So, where is here the big advantage?? Erik, such "articles" are not written to "inform" engineers about technical issues, but to make them believe that TI has invented something "entirely new". And the statement of the "disproven myth" is plain bogus in my eyes, nasty marketing babble... Kai Klaas |
