This simple power supply, which is equivalent to 2 AAA or AA batteries, was found in an Elektor from the 90's. The transformer has a 4.5 V secondary with a current of 50 mA or more.
This configuration that appears several times with variations on this site is from old American...
This configuration (somewhat critical, as the imbalance of characteristics between transformers can cause...
This circuit is from a Popular Electronics of the 90's. Any power MOSFET can be used. The circuit...