buck-boost vs buck then boost

Buck Converters and Boost converters do different things and I see no reason why you would want to use them in series(Buck then Boost). That would essentially be throwing efficiency away for no reason.

A buck/boost converter is one capable of EITHER buck or boosting an input level but not both at the same time.

Here is your example you have 50VDC and you need 12VDC... Buck converter to the rescue bucking that 50 down to 12. Later you want the same 12VDC out but you only have a 5VDC input... not to worry the Boost converter springs into action boosting your 5VDC to 12VDC.

Now lets think about a Buck then Boost converter you again have 50VDC input and you need 24VDC out so you buck that 50 down to 12VDC with 87% efficiency meaning you only threw away 13% in the conversion but now you want to boost it up to 24 at say 80% efficiency so you just threw away another 20% in that conversion. It makes no sense when you could have just bucked from 50 to 24V directly with only one conversion loss.

It is however not uncommon to buck or boost to a level slightly higher than you need so that you can follow it with a linear regulator for precision/cleaning purposes.

Hope that helps

 

Good to know.

 

Wow, 10 years later and 2 Mods answer!.
Just saying....

Martin