This adjustable power supply build around LM723 provides output voltage between 0 and 30 volts at a maximum current of 1 Amp. Because the standard LM723 circuit minimum output voltage is 2 volts, to the ground of the integrated circuit terminal (pin 7) is applied - 4.7 volts, using Zener diode D4. R8 resistor limits the maximum output current, which in this case is 1 ampere.
Using MAX668 integrated circuit you can build a very simple and high efficiency step up converter electronic circuit. This step up converter power supply circuit based on the MAX668 integrated circuit is a high efficiency step up converter that will provide an fixed output regulated voltage around 12 volts at a maximum output current of 2.3 amperes . This step up converter circuit will provide a 12 volts output voltage from a 3.3 to 5.5 input voltage .