Using MAX630 CMOS step up regulator can be designed a very simple high efficiency (85%) 3 to 5 volt converter electronic project .
This step up converter based on the MAX630 IC will provide a 5V output at 40mA .
When IC (pin 6) is driven low, the output voltage will be the battery voltage minus the drop across diode D1.
The optional circuitry using C1, R3, and R4 lowers the oscillator frequency when the battery voltage falls to 2.0V.
This lower frequency maintains the output-power capability of the circuit by increasing the peak inductor current, compensating for the reduced battery voltage.
As you can see in this electronic project you will require just few external electronic components to design a compact , high efficiency 3 to 5 volts converter circuit .