Low power small voltage source to charge high voltage storage

[raff5184]

Hi,
what is normally used (if it is even possible) to completely charge a storage such as a capacitor or supercapacitor that has say 5-6V or even 15V of maximum rating voltage if the charging source is a low DC power (4-5mW) and can't reach the 5V, but is a 1V or 2V source?

[David Hess]

A boost switching regulator would commonly be used but several other switching regulator topologies are suitable also.  There are dedicated "energy harvesting" ASICs intended for this application now.