| ??? 12/08/05 15:22 Read: times |
#104889 - Paralleling is only a theoretical remedy Responding to: ???'s previous message |
Farshid said:
From the last topic that i brought here I remember that Kai have been said it is necessary to use a small resistor about 1 ohm across the Ferrite Beads (named BL2n02 ?) used at the input of regulators. This was to stop the LC filter from showing self resonating. I have had a look into all former posts from me, where I discussed BL02RN2, but I couldn't find where I should have suggested to put the 1R resistor in parallel to this ferrite choke. But many places where I suggested to put it in series to BL02RN2. I would never recommend to put an 1R resistor in parallel to a ferrite choke, because then the impedance of this effective filtering element (parallel circuit of resistor and choke) could only be smaller than 1 Ohm! And this where a good ferrite choke can show hundreds of Ohm between 10MHz and 1Ghz!! So, paralleling is not at all a good idea. Nevertheless, I found it discussed in the application note from Philips, and was very surprised to find such an unproper recommendation in an official release. Paralleling is at least a theoretical way to suppress ringing, as solving the according differential equation shows this, but should not be followed in practice, because much, if not all of the dampening is wasted, the more the samller this paralleled resistor is. Kai |
| Topic | Author | Date |
| Vcc Line Filtering | 01/01/70 00:00 | |
| what are the resistors across the ferrit | 01/01/70 00:00 | |
| Some suggestions | 01/01/70 00:00 | |
| RE : Some suggestions | 01/01/70 00:00 | |
| I still would like to know | 01/01/70 00:00 | |
| LC-filter versus regulator | 01/01/70 00:00 | |
| Excellent | 01/01/70 00:00 | |
| That's really good, i was thinking that | 01/01/70 00:00 | |
| I have never used any such amd never had | 01/01/70 00:00 | |
| Filter position | 01/01/70 00:00 | |
| voltage drop for a ferrite at milliamps | 01/01/70 00:00 | |
| Line regulation | 01/01/70 00:00 | |
| sorry, that was tongue in cheek, of cour | 01/01/70 00:00 | |
| my bad | 01/01/70 00:00 | |
| if anyone should be sorry, that would be | 01/01/70 00:00 | |
| SMD,RC | 01/01/70 00:00 | |
| do you remember the math in a previous p | 01/01/70 00:00 | |
| Voltage Drop | 01/01/70 00:00 | |
| Murata better than others? No... | 01/01/70 00:00 | |
| Paralleling is only a theoretical remedy | 01/01/70 00:00 | |
| my mistakes... | 01/01/70 00:00 | |
| How many filters... | 01/01/70 00:00 | |
Tada! | 01/01/70 00:00 | |
| Exactly | 01/01/70 00:00 | |
| Thanks Kai | 01/01/70 00:00 |