At 01:48 AM 6/24/02 +0200, Tal Bejerano - AMC wrote: >I draw again the PSU section. can you tell if all grounds ok? Not good, Tal. Look at the problem this way. The transformer charges up the capacitors during a a very brief time period near the peak of each half-cycle. The peak current is MUCH higher than the average current. What you have shown is one of the worst ways to lay out a power supply. When the diodes start to conduct, there will be a significant voltage drop on that trace between the center tap of the transformer and the main filter capacitors. That voltage drop adds to and subtracts from the reference point on the regulators (the ground terminals). Voila! You have just added ripple to the supply rails. What I would do is make the trace between the transformer CT and filter caps as thick as you possibly can. Then make sure you take the ground point for the voltage regulators from the filter cap, NOT from the transformer CT. It sounds as if you already have a board made up. Try this. Run some heavy wire between the leads on the filter caps and the transformer center tap. Use 14 AWG wire or larger and just lay it down on the underside of the PCB. Solder it into place. Cut the trace that connects the voltage regulator grounds to the CT and jumper it to one of the filter caps instead. See if it makes a difference. Is it worse? Better? Try thickening up that wire between the filter caps and the transformer CT - lay another 14 AWG wire down beside the existing wire and solder the whole mess into one large conductor. Use your existing board to play with the grounding until you get the best result. Then make the changes to the artwork. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.