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buck-boost vs buck then boost

Discussion in 'General Electronics Discussion' started by Zeropluszero, Jun 22, 2010.

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  1. Zeropluszero


    Jun 11, 2010
    hey guys,
    does anyone know the difference between a buck-boost converter and a buck then boost converter?

    thanks a lot!
  2. NickS


    Apr 6, 2010
    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
    Last edited: Jun 22, 2010
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Boost before buck has at least one use - it can improve the power factor of a mains operated switchmode power supply.

    I'm equally unsure as to why you might buck then boost.
  4. NickS


    Apr 6, 2010
    Good to know.
  5. bertus

    bertus Moderator

    Nov 8, 2019
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Buck then boost works only if the input voltage is always higher than the intermediate, stepped down voltage.
    A buck-boost converter creates an output voltage from an input voltage that is either higher or lower than the input voltage.
  7. Martaine2005


    May 12, 2015
    Wow, 10 years later and 2 Mods answer!.
    Just saying....

    Minder, davenn and Hunter64 like this.
  8. davenn

    davenn Moderator

    Sep 5, 2009
    Yeah, should have been closed and not answered !!
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    I only I had looked at the op's date ;)
    Martaine2005 likes this.
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