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Opinions about SEPIC versus Zeta converters

treez

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OK, i am sure you know that VMC is a little harder than CMC, because CMC results in cancellation of one of the LC poles , since it controls the current in the inductor.
Also, in VMC you need a source sense resistor and comparator anyway, so as to put a clamped maximum on the fet current.........so people often then just use that resistor to do CMC with.
CMC needs slope compensation, but not when in DCM...and not when constant off time control is used.
 

treez

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Hi,
Here are some constant off time uncoupled sepics. One is a solar sepic, and regulates its input current to 2A maximum…but this gets over-ridden by an error amplifier “looking at” the vin and brakes the sepic if its vin tries to go below 2.8V (like in MPPT algorithm).
Constant off time makes light work of uncoupled sepics.

There is also an inrush circuit on one of them.

Also there is pdf and ltspice sim
 

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Easy peasy

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a pk current mode controlled sepic will also reduce the order of the power system - i.e. allow a faster control loop - as will average current mode control ...

pk current mode control needs slope comp above about 48% on time of the input side mosfet ...
 
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