Gennette Bruce says:
Here is a simple idea that works really well to isolate noise generating sections of a circuit from sections that need clean power - it uses just 3 diodes and 1 extra capacitor.In the common leg of a 3 terminal regulator you add a diode that raises the regulator's output voltage by the drop across the diode. You then fit 2 identical diodes to the output from the regulator to drop the voltage back down to where it would have been. Separate smoothing capacitors are then fitted to the 2 separated outputs.
The really cool thing is that the outputs from the 2 diodes are completely isolated from each other and can be used to power an analog AND a digital circuit from the same regulator.
1N4004 diodes that cost less than 10 cents are rated at 1amp/400volts and 470uF caps are about 60 cents, so you can add this second output to your existing analog power supply for less than a dollar to give you a separate digital power supply.
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