| ??? 07/16/09 13:12 Read: times |
#167416 - Sideplating? Thermal vias? Responding to: ???'s previous message |
Lukas said:
One more qustion - I saw a pcb layout where a lot of small ground vias were close to edge of the board, not in parallel. It looked like a riveting. Is there any special meaning of this? You possibly mean sideplating? Ot thermal vias? Lukas said:
Yes, the switcher's gnd is connected to the common gnd. It is realized by the FB in my case. I am going to remove it and connect switcher's gnd directly as you suggest. And what about Vcc behind the output cap? There is also FB in my schematic. Should I remove it too or not? This depends a bit on your application. Usually, the output voltage shows some ripple at the switching frequency. In mixed analog digital applications you normally wish to reduce this ripple by adding a second LRC low pass filter. These parts and the output cap form a pi-filter which can work very effectively. For reducing the ripple by the help of this filter the inductance should be able to provide enough impedance at the switching frequency. So, it might be better to use the same inductance you already use at output of switcher. A ferrite bead is not so good at the switching frequency. The cap at output of this filter can have the same value like the cap at output of switcher. Sometimes a small resistance is needed in series to the inductance to damp ringing. Its value should be about R = SQRT(2 x L / C). Often the caps and the inductance already show enough damping series resistance so that the resistor can be omitted. Lukas said:
My device could be powered from 9 - 15 V AC. So there is a rectifier. Should I place the FB(s) between the rectifier and the input cap to keep the input cap on the switcher's ground plane? Should I place it(them) at both of the poles of the rectifier or only at +? In this case, you will have spiky rectifier currents, which must not flow across the common ground plane. Connect the plus and minus pole of rectifier directly to the input cap, without connecting the rectifier terminals elsewhere to the common ground. You can omit the FB here. By the way, 10...47nF caps across the rectifier diodes are helping the rectifier to survive surges and bursts from mains... Kai |
| Topic | Author | Date |
| PCB design - ground plate... | 01/01/70 00:00 | |
| excuse... | 01/01/70 00:00 | |
| You can use a local ground plane, but... | 01/01/70 00:00 | |
| So, if I understand it well... | 01/01/70 00:00 | |
| Yes, of course, but... | 01/01/70 00:00 | |
| Yes, but... | 01/01/70 00:00 | |
| No overlap | 01/01/70 00:00 | |
| Version B, but without FB... | 01/01/70 00:00 | |
| so... | 01/01/70 00:00 | |
| PCB layout... | 01/01/70 00:00 | |
| Answers... | 01/01/70 00:00 | |
| EMC | 01/01/70 00:00 | |
| Hhm, I wouldn't do that... | 01/01/70 00:00 | |
| AC power supply | 01/01/70 00:00 | |
| ground vias | 01/01/70 00:00 | |
| Locating of vias... | 01/01/70 00:00 | |
| Thank you very much... | 01/01/70 00:00 | |
| Sideplating? Thermal vias? | 01/01/70 00:00 | |
| Stackup | 01/01/70 00:00 | |
| Not such a good idea | 01/01/70 00:00 | |
| interrupted/split planes | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| Thank you... | 01/01/70 00:00 | |
| Nice link, Rob! | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| Explanation | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| What you propose isn't well suited for 4 layer boards | 01/01/70 00:00 | |
Hi Kai | 01/01/70 00:00 |