| ??? 12/06/05 09:06 Read: times |
#104748 - RE : Some suggestions Responding to: ???'s previous message |
Dear Kai,
Thanks a lot for your priceless help. Filtering Before the Regulator : The reason, that electrolytics shouldn't be much higher than above values, is that if input capacitor is in the same range as storage capacitor, relevant rectifier currents will be able run to the regulator forming a larger current loop than necessary, producing lots of aviodable interference. I didn't knew this , i was thinking bigger is better ! - 100nf Capacitor could be Ceramic/Tantalium/MultiLayer which is better ? i were using Tantals. Paralleling a resistor is only a proper option, if an additional series resistor would cause a too high voltage drop in combination with higher currents.
Nevertheless, I would not recommend this option, because lots of dampening is wasted by this methode. When using a series resistor, on the other hand, full impedance of inductance comes into play and very high dampenings can be achieved. That's really good, i was thinking that only a parallel resistor can stop self resonations.I am not concerned into high current needs ,so i'll try to use series resistor since then. All above refers to when we have a one-stage (if i recall the correct pharse here) filtering. we have disscussed about Ferrite Beads ,The ones who show high impedance at higher frequencies (10-1000 Mhz), sometime ago. If i remember correctly they were not good at filtering lower frequency noises.this wasn't the problem that time cause lower frquencies were removed by the aid of the regulator.But what if the input Vcc is also being used in the circuit ? do i have to use a second filter to filter frequencies lower than 10 Mhz (Down to my desired frequency) by the aid of another LC filter? If yes were do i hvae to use this filter , before the First one or After it ? Filtering after the Regulator : Using 4 capactiors and a resistor and an inductor a very good filtering will be provided to the MCU.This very good filtering is necessary in some boards but not in some others. - If the MCU is not drawing more than 20mA could i use only a simple RC filter instead of the pi-filter ? - For supplying the Analog Supply in some MCUs or DACs i always use a RC filter after routing a separate trace from near the output of regulator.Is it alright ? (Circuit F) I'll try to read the PDFs specially the one by Philips. Circuit G is the one that i drawed considering considering your help.could you please confirm that is it alright ? 
Again thanks for all your help. Farshid |
| 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 |