Bob Tims <[email protected]> wrote > Happy New Year All,
>I have an interesting noise problem brought to me. The noise is >a 500-900 mV pulse seen at 50 MHz on a power lead from a DC to >DC converter (48V to 5V) to a VME cage. There were two >scenarios: first, both the power supply and the cage are >earth-grounded, and the pulse is seen at both the power supply >and the cage. Second, the cage is left floating, and the pulse >is only seen at the power supply. The noise seems to be a ring, >and the leads between the supply and cage are fairly long. Has >anybody seen something like this before, or does anybody have >any suggestions or comments? We have several ideas, but not much >time. The frequency and the fact that the pulse reaches almost a >volt concerns us greatly. Thanks in advance, Dear Bob We experienced similar problems due to DC/DC converters or switched power supplies. Since the output of the power supply was not filtered enough on common mode (i.e. with respect to "ground") we had similar damped sine waves on DC power leads. If your 5V voltage can be grounded (I mean "0V" shorted to the cage) than do it with the shortest wire you can. Be shure that the wire is not longer than 5 cm and is of low inductivity. This helped in our case, hope it helps in your case. If your 5V voltage must be floating with respect to the cage or other conductive enclosures or objects in the proximity of your electronics, place some 100nF between "0V" and that enclosure. Good luck -- ************************************************************** * Dr. Georg M. Dancau * HAUNI MASCHINENBAU AG * * [email protected] * Manager EMC Lab * * TEL: +49 40 7250 2102 * Kampchaussee 8..32 * * FAX: +49 40 7250 3801 * 21027 Hamburg, Germany * ************************************************************** * home: Tel: +49 4122 99451 * Hauptstr. 60a * * Fax: +49 4122 99454 * 25492 Heist, Germany * **************************************************************
