In a message dated 12/27/00, Zohar Zosmanovich writes:
> I'm concern about designing a proper protection from Surges, applies on > ports for indoor signal lines (E1, Ethernet) at telecommunication centers. > According to ETSI EN 300 386 a surge of 1.2/50 us, 0.5 kV shell be applied > between Tip & Ring. Because of lack in space on the PWB we can't put the > overvoltage protector (sidactor, TVS) isolation transformer and ... close to > the connector were we applying the surge. My questions are: > > 1. Can I locate only the Sidactor close as possible to the connector, while > the isolation transformer is about 45 cm ahead ? > 2. Can the trace width after the sidactor, till the transformer, be thin as > 5 mills? > Hi Zohar: It's not clear to me that you need a sidactor to pass this test. The EN 300 386 surge is applied common mode (tip/ring to ground), so there should not be much in the way of a differential voltage between tip and ring. Assuming your interfaces are transformer coupled, and if the transformers have at least 500 volt isolation, the common mode surge should not damage anything since there is no path to ground. This assumes that your board layout can handle 500 volts from tip/ring to ground. It should not be hard to accomplish this, especially if you use internal layers. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
