IIRC, all the coupled-capacitor topologies (zeta, sepic, cuk...) have multiple RHP zeros. The sepic has two (maybe three?). So the control loop will need to be somewhat slow, if you're operating in CCM. Usually some damping is applied to the coupling capacitor to mitigate this.Thanks for the feedback. Love to know about your experiences regarding its being hard to stabilize. In these months of simulating three different SEPICS with load steps of 10mA to 1.3A and different loads and Vin min to Vin max, etc., they all supposedly function well with a type 3 compensation that is not far from fSW (100kHz) and 94uF Cout, fb taken at load point - this seems dubious to me as all literature says feedback loop of 1/3rd to 1/10th fSW and RHPZ and second-stage filter reduce/limit bandwidth...
Cuk converter. Can be isolated if you want a positive output voltage. Even nastier transfer function though (four RHPZ if I recall correctly).Shame there isn't a hybrid SEPIC input and Zeta output (no current ripple either end and very low Vout ripple) design afaik.
your ckt is missing a choke - has diode instead ...?
Although you are correct that the current's direction in a diode which "would replace" L2 is similar, the reality is that an inductor stores energy in the form of current, whereas a diode only steers the current without storing any energy.
another newbie oversight - when the fet turns on there is an enormous current pulse as it shorts out the blocking cap via the diode that shouldn't be there ... and discharges it to zero every time, without contributing anything to the o/p - but rather to watts and stress in the mosfet ....
[LAUGHS]
Hi Akanimo,
Not sure what you mean by switching and averaging. Component values are all in schematic, awol L2 is also 100uH. It was just messing around, as two people have pointed out contras to doing that with a SEPIC, I'll leave that experiment there but curious as to what you think could be done with it.
Okay, I'll plot the frequency response of you converter and see what there is. How about the input voltage range and auxiliary voltage value?...L2 is also 100uH
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