| ??? 08/16/11 15:18 Read: times |
#183378 - capacitors... Responding to: ???'s previous message |
Lukas said:
I don't understand why there is no information about the cap in AM1D-0505SZ DC/DC convertor datasheet... Your DC/DC-converter switches only at 80kHz, but the Traco-switcher is faster (400kHz). So, maybe there's no urgent need for this cap to pass the CE testing. But in any case your design will profit from such a cap, especially if the long lines of a RS485 are connected to the output ground and act as perfect antenna... Lukas said:
and do you know how to obtain the value for this capacitor? Well, this cap must withstand Surges and ESD, so must be rated in the kV-range. You know by yourself how difficult it is to get a big ceramic SMD cap rated in the kV-range... The exact value of this cap doesn't really matter unless you suffer from the most demanding interferences. From some hundred pF to dozens of nF, everything will work that decreases the impedance from input ground to output ground for the switching frequency and its harmonics and provides a path back to the origin of switchings, which sits in the input circuitry of DC/DC-converter. But take care that this cap can withstand Surges and ESD. Even a 4n7 Y-cap like the PME271 will sufficiently work when being soldered directly to the pins of DC/DC-converter. Lukas said:
...and it is also between Vin+ and Vout+. This cap can be omitted if you have an output filtering cap connected from the output voltage pin to the output ground pin of DC/DC-converter. Lukas said:
I have 1nF/2kV 1812 available, so can I use this one? Yes. Put some in parallel to make it more robust against ESD, though. Lukas said:
But first, I will remove the 100R resistor as you suggest... These 100R resistors are to deal with hum loops. If your design avoids hum loops, then there's no reason to have them. If you are not sure, at least decrease them to about 10R or so. Lukas said:
...and insert the capacitor between the earth GND and signal GND. The cap at the DC/DC-converter could serve as this cap. The input ground of DC/DC-converter is connected to PE via the personal computer, isn't it? Kai Klaas |
| Topic | Author | Date |
| Problem with RS232/RS485 converter... | 01/01/70 00:00 | |
| More info please | 01/01/70 00:00 | |
| probably | 01/01/70 00:00 | |
| more info... | 01/01/70 00:00 | |
| yes,i think | 01/01/70 00:00 | |
| input impedance | 01/01/70 00:00 | |
| i'm wrong | 01/01/70 00:00 | |
| what is the right value? | 01/01/70 00:00 | |
| did You tryed capacitor? | 01/01/70 00:00 | |
| thanks... | 01/01/70 00:00 | |
| it works...! | 01/01/70 00:00 | |
| congrats | 01/01/70 00:00 | |
| shape | 01/01/70 00:00 | |
| dont | 01/01/70 00:00 | |
| It is OK. | 01/01/70 00:00 | |
| Hints... | 01/01/70 00:00 | |
| schema | 01/01/70 00:00 | |
| Repair... | 01/01/70 00:00 | |
| transils... | 01/01/70 00:00 | |
| RS485 | 01/01/70 00:00 | |
| Sample Schematic | 01/01/70 00:00 | |
| Thank you very much for the schema... | 01/01/70 00:00 | |
| AVX varistors... | 01/01/70 00:00 | |
| capacitor | 01/01/70 00:00 | |
| capacitors... | 01/01/70 00:00 | |
| GNDs | 01/01/70 00:00 | |
| 1992 | 01/01/70 00:00 | |
| Thanks... | 01/01/70 00:00 | |
Links... | 01/01/70 00:00 |