This circuit provides a reference voltage of 2.5 V adjusted in the trimpot. The transistor can be the BC558 (in the drawing it came out as NPN). The control is done by a rectangular input signal.
This circuit was found in an English magazine Radio & Electronics Constructor of February 1977....
I found this circuit in a Popular Electronics from 1992. The circuit shows how we can use two...
March 2017 - Texas Instruments LM5166 Synchronized Buck Converters are available at Mouser for 3V...