Here we want multiplicate the source voltage 5 VDC. A 555 converts it in an alternate signal that allows to use a Greinacher circuit on the 555 output.
Greinacher circuit is composed of several stages (you may add as many stages as you want).
Each stage is composed of 2 condensators and 2 diodes.
First stage rectifies and multiplicates average voltage of the output signal.
Then each new stage multiplicates voltage by 2.
Here are 3 stages and final output voltage is about 24 VDC.
You can add as many stages as required up to kVolts.
