Small appliances have microcomputer that requires 5V power supply. Why it can use only 1.5V battery? The 1.5V to 5V boost converter circuit inside them.
This is 5V 3A Switching Regulator circuit by LM2576-5.0 is simple switching power supply 3A step down regulator for power digital circuits. [...]
This is 5V switching regulator circuit using transistor, decreases voltage or Step down voltage converter circuit, decrease 6-18V into 5V at current 100mA.