| ??? 05/27/05 23:05 Read: times |
#94027 - Ferrite on cables and filtering Responding to: ???'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 ? http://www.8052.com/users/farshidjh/IMG_3885.JPG In combination with 220µF you get a corner frequency of fc = 1 / (2 x pi x SQRT(220µF x 220µH)) = 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. |
| Topic | Author | Date |
| Info on Murata Inductors for LC filter ? | 01/01/70 00:00 | |
| Ground routing and filtering | 01/01/70 00:00 | |
| Examples of soft ferrites | 01/01/70 00:00 | |
| good link | 01/01/70 00:00 | |
| Ground routing | 01/01/70 00:00 | |
| Ground routing techniques | 01/01/70 00:00 | |
| Ferrite on cables and filtering | 01/01/70 00:00 | |
| Answers... | 01/01/70 00:00 | |
| many of my questions are answered ! :) | 01/01/70 00:00 | |
| Long lines | 01/01/70 00:00 | |
| the other reason | 01/01/70 00:00 | |
| Buffers good ! | 01/01/70 00:00 | |
my next PCB would be way much better ! | 01/01/70 00:00 | |
| BL02RN2 in Tehran | 01/01/70 00:00 | |
| thanks a thousand dear payam | 01/01/70 00:00 | |
| On-Board Type EMI Suppression Filters | 01/01/70 00:00 | |
| Basics of EMI Filters | 01/01/70 00:00 | |
| More... | 01/01/70 00:00 | |
| Tell me when it's enough | 01/01/70 00:00 | |
| you're doing a favor for me! | 01/01/70 00:00 | |
| Not all available in Tehran probabely// | 01/01/70 00:00 | |
| BL02RN2 Datasheet | 01/01/70 00:00 |