Buck converter - CCM and DCM operation:
***Allow 30 secs for the circuit to reach steady state***
There are two main current loops in CCM, one is active during main switch ON time D*Ts, the other during main switch OFF time (1-D)*Ts when the freewheeling diode conducts.
Notice that if inductor value is high enough then the inductor current is continuous and never falls to zero (CCM-continuous conduction mode). Also, all the ripple current is taken by the capacitor and the load gets only the DC current. The input current is of pulsating shape.
If we lower the inductor value to approximately 4uH then the inductor current falls nearly to zero, this is called BCM or boundary mode operation.
If we further lower the value to 2uH then the inductor current stays at zero for a certain amount of time bringing the converter in DCM or discontinuous mode. Notice that during this time the load current is supplied by the capacitor.
For further info and to see design formulas with component selection steps visit the blog page at:
http://j.gs/5535160/buck-formulas
