Yasser, 1. There is no way to answer your ground question with the information you have provided. Cutting up a ground or having multiple ground layers has to be decided on a case by case bases. Unless you are careful with routing of traces with a cut up ground you will cause far more problems than you solve. Placement of components is just as important. There are a number of good books available that go into the details needed to make good decisions. The IEEE has several good books as do others. You can also find information in the past EMC Symposium notes, which are available on CD at http://www.ewh.ieee.org/soc/emcs/news9.html. Having said this, we typically use a common ground plane on our boards, but no always.
2. As scopes have a input impedance of greater than 10Meg ohms it is normal for them to see 50/60Hz from transformers and overhead lights. Circuits tend to be a much lower impedance and tend not to be affected by the 50/60Hz. 3. We select our fuses based on input from the transformer company, the Safety Standard we are trying to meet, and the design guides that the fuse companies publish. Jim Jim Bacher, Senior Engineer Paxar - Monarch e-mail: [email protected] voice: 1-937-865-2020 fax: 1-937-865-2048 ____________________Reply Separator____________________ Subject: request for help Author: "yaserh" <[email protected]> List-Post: [email protected] Date: 11/1/00 8:21 AM Hi, * I need to ask if i have a PCB board with analog and digital circuits, is it's right to connect the digital and the analog GND to the GND layer or i must create two Gnd layers and connect them at the Gnd entery point to the board. * I have another problem with a circuit i have designed uses a linear power supply with a transformer 220-12 VAC 1A , when i measure on any point on the circuit with respect to the earth point i found 110 VAC on the scope. I need to know why i see this 110 VAC or this is due to the transformer interwinding capactance, if it's so how i can remove this signal from my circuit. I think that this is a common mode signal. * I need to know how can i select the value of my fuse instaled on the primary side of 220 VAC transformer. I have a board with transformer of 12 VA and 220 VAC input and it uses a fuse 3.15 A how the designer of this board select this fuse. Waiting your reply With my best regards Yasser El-haddad ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
