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    Boost operation in inverting Buck-Boost converter

    Hi,

    Regarding the inverting BUCK-BOOST shown in figure, I understand how it works as Buck. Please explain how it can act as a BOOST. Because during the off time there is no connection with input supply, So i think it cant act as boost. Then why its name as "BUCK-BOOST" ?...

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    Re: Boost operation in inverting Buck-Boost converter

    It does not matter if for some amount of time the inductor is not connected to the supply, the only thing that matters is the energy the inductor has stored during the ON state. If one stores a lot of energy in the inductor, then that energy is passed to the cap, boosting its voltage. That is the reason why this works as boost only at high duty cycle (>0.5), you store energy for the major part of the cycle, while decrease the energy for only little part of the cycle.



    •   Alt14th February 2018, 12:50

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    Re: Boost operation in inverting Buck-Boost converter

    it also works as a boost at any duty cycle if the load is light enough, e.g. for no load, the o/p voltage will climb even for D = 0.05%

    it is a power or energy transfer topology, so if loaded too heavily the o/p volts will be low even for D>0.5 - thus volt regulation of o/p is always needed.



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    Re: Boost operation in inverting Buck-Boost converter

    So that means, even the normal buck converter can act as Boost and for heavy loads it cant boost ?



    •   Alt15th February 2018, 06:40

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    Re: Boost operation in inverting Buck-Boost converter

    The inductor voltage can rise upto input supply voltage right?



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    Re: Boost operation in inverting Buck-Boost converter

    So that means, even the normal buck converter can act as Boost and for heavy loads it cant boost ?
    The normal Buck acts as a boost only if you swap the input with the output and vice versa.

    The inductor voltage can rise upto input supply voltage right?
    As soon as the switch is closed, its voltage is already there.



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    Re: Boost operation in inverting Buck-Boost converter

    The normal Buck acts as a boost only if you swap the input with the output and vice versa.
    See the contradiction, on that case the boost is happen with voltage in the inductor plus the input voltage source. that is, an external source (inductor voltage) is there to add up.



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    Re: Boost operation in inverting Buck-Boost converter

    You can consider the inverting buck boost as a single inductor flyback converter. All energy transferred from input to output has to be stored intermediately in the inductor. That's different from a non-inverting buck or boost where only part of the energy is stored in inductor.



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    Re: Boost operation in inverting Buck-Boost converter

    Then it is also applicable to normal buck converter right?. How can we say " in inverting, all energy stored by inductor while in non inverting it is not"?. Although both have same type of working (not configuration)



    •   Alt19th February 2018, 13:20

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    Re: Boost operation in inverting Buck-Boost converter

    Hi,

    How can we say " in inverting, all energy stored by inductor while in non inverting it is not"?. Although both have same type of working (not configuration)
    look at the current flow
    1) through the inductance
    2) to the load
    * when switch is closed
    * when switch is open

    For both converter types.

    Klaus
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