Small Zener diode voltage regulator circuit with PCB, using transistor and few parts. it is simple and cheap fixed dc source circuit. As one of best choice.
How to make it light long time or use battery longer than usual. we use this Switch mode LED driver circuit using transistors. and simple circuit below [...]
This is a DC to DC Buck converter working principle. We often use it as a step down DC to DC converter circuit. Because it is a switching mode power supply.