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Farshid Jafari Harandi
05/27/05 17:05
Read: 987 times

#94027 - Ferrite on cables and filtering
Responding to: Kai Klaas's previous message
Mr Kai ,

I realy appreciate for your help.

Good filtering prevents noise from entering your circuit at every vulnerable point. So, you need filtering at every cable which enters or leaves your board

i have a relay board consist of 24 relays which is fired this way :
Main board (MCU AT89S52) -> prepherial board (74HC541->74LS138->74HC164) -> relay driver board (74LS541->ULN2803->relays)
it's a long way ! but i think these should buffer the switching from the main board enough ?

- cables going to the prepherial board is a 28AWG flat cable connected to diffrent port pins of the MCU.with no ground in between of each wire, just a common ground signal.

- cables going to the relay driver board is a 40 pin 28AWG flat cable with a connector same as IDE with ground between each signal ,grounded at one end in the prepherial board (near the HC168 outputs).

do i have to use a toroidal ferrite on these cables ? how should i wound the cable around the ferrite ? a sample winding(the flat cable around the toriod) i seen in my Camera's USB cable is seen in the below picture.
is this right,how big the toroid or ferrite have to be ,or what should be the specification of the ferrite ?

In combination with 220F you get a corner frequency of fc = 1 / (2 x pi x SQRT(220F x 220H)) = 723Hz. This will give a very nice low pass filter.

Now i know how to calculate the corner frequency . TADA !

And even if the effective inductance might be much lower than that of your triac choke, they will provide much better noise rejection at very high frequencies, just because their impoedance is much higher there than that of a triac choke, suffering from interwinding capacitance!

do you mean Toroidal Cores by 'triac choke' ?
it's good to hear that the inductance value isn't critical.
so what about the amperage rating of the inductor ?
maybe its better to get a suitable core and then wound myself some filters.question is how to calulate the inductance ? do you know a good website or tutorial to learn how to measure inductance using a standard digital multi meter or with my old 10MHz scope.
and about the SMD filters i'll have to search the market hoping to find some.

Then only filtering in front of 5V regulator will help

just in case , i'm interested to know what happens if i use this filter before the 5V regulator ?

thanks for your help.

Farshid J.H.

List of 22 messages in thread
Info on Murata Inductors for LC filter ?      Farshid Jafari Harandi      05/27/05 03:55      
   Ground routing and filtering        Kai Klaas      05/27/05 04:57      
      Examples of soft ferrites      Kai Klaas      05/27/05 05:07      
         good link      Farshid Jafari Harandi      05/27/05 17:13      
      Ground routing      Mehdi      05/27/05 07:24      
         Ground routing techniques      Kai Klaas      05/31/05 04:34      
      Ferrite on cables and filtering      Farshid Jafari Harandi      05/27/05 17:05      
         Answers...        Kai Klaas      05/31/05 05:18      
            many of my questions are answered ! :)      Farshid Jafari Harandi      05/31/05 12:16      
               Long lines      Kai Klaas      06/01/05 08:50      
                  the other reason      Erik Malund      06/01/05 09:24      
                     Buffers good !      Farshid Jafari Harandi      06/01/05 17:18      
                  my next PCB would be way much better !      Farshid Jafari Harandi      06/01/05 17:18      
   BL02RN2 in Tehran      Payam Soltany      05/27/05 20:10      
      thanks a thousand dear payam      Farshid Jafari Harandi      05/28/05 09:28      
         On-Board Type EMI Suppression Filters      Payam Soltany      05/28/05 18:37      
         Basics of EMI Filters      Payam Soltany      05/28/05 18:38      
         More...      Payam Soltany      05/28/05 18:40      
         Tell me when it's enough        Payam Soltany      05/28/05 18:43      
            you're doing a favor for me!      Farshid Jafari Harandi      05/28/05 19:49      
               Not all available in Tehran probabely//      Payam Soltany      05/28/05 20:40      
               BL02RN2 Datasheet      Payam Soltany      05/28/05 21:13      

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