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I needed a bipolar power supply simulating two 9V batteries (6LF22). I decided to build it based on a 24V power supply. The circuit is quite simple, it uses only 3 transistors, 3 resistors, 3 capacitors and 3 zener diodes, one of the PNP conduction transistors (I used 2*2N2222 and 2N2907). The circuit was calculated specifically for these transistors. The supply voltage can be changed from 18V to 30V, but keep in mind that 3 volts will be lost. Max current is 0,05A, or need change transistors.
---UPD---
I added reverse polarity protection, a smoothing inductor, changed the resistor ratings to reduce power dissipation, and also added indicator LEDs through which the capacitors are discharged. It's safer now.
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