3 to 12 volts converter using ADP1621

This power supply circuit diagram is based on the ADP1261 fixed-frequency, pulse-width modulation (PWM), current-mode, step-up converter controller. It drives an external n-channel MOSFET to convert the input voltage to a higher output voltage. The ADP1621 can also be used to drive flyback, SEPIC, and forward converter topologies, either isolated or nonisolated.

The ADP1621 eliminates the use of a current-sense power resistor by measuring the voltage drop across the on resistance of the n-channel MOSFET.

The circuit presented here will provide a maximum 12 volts output at a maximum 1 ampere current from an 3.3 volts input supply voltage .

D2 is a common signal diode , D2 can be a Vishay SSC53L diode and M1 transistor can be IRF7470 .
Resistor, R3, of 700 Ω is placed between VOUT and the IN and PIN pins to limit the input currents because the IN and PIN pins are regulated to 5.5 V. A diode, D2, is placed between VIN and the IN/PIN pins to supply the necessary quiescent current to start the ADP1621. Once the ADP1621 starts and the output voltage reaches 12 V, the quiescent current stops flowing through D2 and is supplied by the output.