A synchronous buck converter is a modified version of the basic buck converter circuit topology in which the diode is replaced by a second switch. This modification leads to an improvement in efficiency.
That's because of the standard voltage drop of around 0.7 volts in a diode. If we change the diode with a mosfet that have a well selected on resistance (for example 0.015 ohms) we can reduce signifficantly the power loses on the component and by that way increase the efficiency, especially in the case that we want to deliver very low voltage (for example 10% of the input voltage) from an already low input voltage.
Another great advantage is that this converter never enters discontinuous mode. That's because the switch is bidirectional and allows reverse flow of current. Also that feature allows inverse flow of power from output to input.
In a buck converter by varying the duty cycle of the mosfet we can decrease the DC input voltage by a factor of D (where D is the duty cycle). In the example we can set the output voltage by varying the potentiometer viper position (the percentage of the viper position give us the percentage of the input voltage that we deliver in the output).
This is an open loop control method of a synchronous buck converter. If you want to see a closed loop control method of a synchronous buck converter check my circuit named "Synchronous Buck Converter Controller".
