John- My SWAG: check the secondary voltages. Are they holding firm at 15V AC or are they tracking the output voltage of your dialed in voltage? Brian -----Original Message----- From: John Midgley To: PICLIST@MITVMA.MIT.EDU Date: Wednesday, February 18, 1998 7:52 AM Subject: (OT-ish) PIC Power Supply Well, quite OT actually I'm filling in a few days before my PIC programmer arrives by constructing a power supply. Simple job. Couldn't be easier. Doesn't work. Then I connect them together; they share the series-connected dual windings of a 15V transformer (to give 30V), a bridge rectifier, and earth. Now each 'tracks' the other, so that if I've got +20V and -20V 'dialled in' on the two pots, when I reduce to, say +10V, the negative rail slowly approaches -10V. Now if I dial in -5V, the positive rail reduces to about +5V. The way the 'uncommanded' voltage changes looks like a curve of a cap, charging (or discharging) through a resistor. There is a 10uF cap from the 'adj' pin to ground 'to improve ripple rejection'.