It is typical circuit of buck so we are considering the load is a constant resistance, probably a load resistor but practically you just think we designed this buck for a micro controller (means replace the load resistor to a microcontroller in an operation mode) so the micro controller take different current eventually so out current will be different
When switch is opened. Voltage across the inductor polarity change due to maintain the current in same direction. Inductor doesn't allow sudden change of current...when polarity change +higher potential comes to anode and negative sign comes to cathode.so diode is forward bias.its start conducting
