Charge Pump Circuit – Getting Higher Voltage from Low Voltage Source
Boost converters are inefficient at low powers, since a lot of energy is consumed just for keeping the regulation on point and driving the power switch. Also, switch mode converters of this type are noisy – this is a problem if you’re dealing with sensitive circuitry. You’re in the uncomfortable position of an over-engineered solution. Linear regulators don’t work in reverse, so that’s ruled out as under-engineered.
Read the complete tutorial here: https://circuitdigest.com/electronic-circuits/charge-pump-circuit-design