This 12V to 24V Voltage Doubler Circuit can increase the operating voltage by as much as 200% and provides an output current capacity between 10 to 20 mA.
A CD4093 dual-input NAND Schmitt-trigger CMOS IC's gates, IC1a and IC1b, have been used to construct a squarewave oscillator circuit.
The gate IC1c is configured to act as an output buffer. The matching transistors Q1 and Q2 are powered by the buffered output of IC1.
The square wave output at the transistor emitters powers the voltage-doubler circuit, that consists of D1, D2, C2, and C3. This produces a two times stepped up output.
Assuming a 12 volt supply, the voltage boosting circuit will generate approximately 18.5 volts at around twenty mA and 24 volts at roughly ten mA.
Always keep in mind to link the additional, empty gate's inputs to the circuit's ground line.