12 V to 9 V DC-DC Converter This DC-DC Converter schematic diagram is very simple with few components, making it easy to build. It can convert 9 volt DC voltage from 12 VDC source. To obtain a much more accurate output voltage, change zener Z1 using 10V and resistor R1 with a 1 Kohm Variable resistor. A heatsink for Q1 is recommended. Very simple circuit to be able to power your 9 volt electronic equipment and some other stuff.