); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY >Poul-Henning Kamp wrote: >> Considering the efficiency and easy availability of switchmode >> supplies these days, I would never bother with a linear regulator >> in a new design. >> >> For instance national has a series of switch mode regulators (LM25xx) >> which just requires a coil and a diode more than the usual LM78xx >> types. >> >> If you are worried about noise from the swichmode, you can add more >> filtering to the output. >> >> >That is a recipe for disaster if one wants a really low noise oscillator. >This is particularly true if one is a beginner. >Reducing the output noise of a switching regulator to 100uV rms or less >is neither easy nor simple.
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). BTW: contrary to popular belief, linear PSUs are NOT inherently noise-free. The cap charging current spikes through the rectifier diodes can produce plenty of EMI/RFI. JDB [not claiming it's easy, just pointing out one route that could be taken] -- LART. 250 MIPS under one Watt. Free hardware design files. http://www.lartmaker.nl/ _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
