buck boost converter operation

[mess123]

Could anyone please tell me how does buck boost circuit operation helps automatically to step up or step down the input voltage to maintain the output voltage constant??

---------- Post added at 15:39 ---------- Previous post was at 15:15 ----------

Is there any range of duty cycle where the operation is buck and is then boost ??

 

[grieblm]

The buck/boost converter changes mode based on the input voltage. If the input voltage > output voltage it operates in a buck mode; otherwise it is working in a boost mode. The change-over point is dependent on the buck/boost converter design. Perhaps you could tell us what part you are using?

 

[leo_o2]

In one of Buck-boost, four switches are needed. It is smooth transient between step-down and step-up.
When D=50%, Vo=Vin.
Vo=Vin*D/(1-D)