Linear Technology have an interesting appnote: http://www.linear.com/pc/downloadDocument.do?id=4159 In this document, Linear Technology's Application Note 70, a switchmode power supply design is presented with less than 100uV output noise, and little RFI. This is achieved by using a switch controller which has controlled output switch slewing, allowing a trade-off between EMI/RFI and efficiency. Methods to measure and control PSU noise are also discussed (IMHO, the EMI sniffer probe in Section J is particularly interesting). An additional measure you could implement is to synchronize the switchers, and shift the switching overtones away from your frequency of interest. Good luck, JDB. [not associated with LT in any way other than having used these chips in very low noise portable digital audio recorders] -- LART. 250 MIPS under one Watt. Free hardware design files. http://www.lartmaker.nl/ ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu