Ćuk converter
The Ćuk converter[1] (Serbo-Croatian: [tɕûːk], English: /ˈtʃuːk/) is a type of buck-boost converter with low ripple current.
Similar to the buck-boost converter with inverting topology, the output voltage of non-isolated Ćuk converter is typically inverted, with lower or higher values with respect to the input voltage.
While DC-to-DC converters usually use the inductor as a main energy-storage component, the Ćuk converter instead uses the capacitor as the main energy-storage component.
It is named after Slobodan Ćuk of the California Institute of Technology, who first presented the design.
For example, the coils may share a single magnetic core, which drops the output ripple, and adds efficiency.
Because the power transfer flows continuously via the capacitor, this type of switcher has minimized EMI radiation.
The Ćuk converter allows energy to flow bidirectionally by using a diode and a switch.
A non-isolated Ćuk converter comprises two inductors, two capacitors, a switch (usually a transistor), and a diode.
The main disadvantage is the high current stress on the switch.
It is connected alternately to the input and to the output of the converter via the commutation of the transistor and the diode (see figures 2 and 3).
The two inductors L1 and L2 are used to convert respectively the input voltage source (Vs) and the output voltage (Vo) into current sources.
This conversion is necessary because if the capacitor were connected directly to the voltage source, the current would be limited only by the parasitic resistance, resulting in high energy loss.
In steady state, the energy stored in each inductor has to remain the same at the beginning and at the end of a commutation cycle.
This implies that the current through each inductor has to be the same at the beginning and the end of the commutation cycle.
As the evolution of the current through an inductor is related to the voltage across it:
it can be seen that the average value of each inductor's voltage over a commutation period has to be zero to satisfy the steady-state requirements.
(Another way to see this is to recognize that the average voltage across any inductor must be zero lest its current rise without limit.)
(D is the duty cycle), and in off state from D·T to T (that is, during a period equal to
As both average voltage have to be zero to satisfy the steady-state conditions, using the last equation we can write:
Like all DC/DC converters, Ćuk converters rely on the ability of the inductors in the circuit to provide continuous current, in much the same way a capacitor in a rectifier filter provides continuous voltage.
This state of operation is usually not studied in much depth as it is generally not used beyond a demonstrating of why the minimum inductance is crucial, although it may occur when maintaining a standby voltage at a much lower current than the converter was designed for.
For isolated version of Ćuk converter, an AC transformer and an additional capacitor must be added.
As the non-isolated Ćuk converter, the isolated Ćuk converter can have an output voltage magnitude that is either greater than or less than the input voltage magnitude, even with a 1:1 AC transformer.
However, the turns ratio can be controlled to reduce device stress on the input side.
Additionally, the parasitic elements of the transformer, namely leakage inductance and magnetizing inductance can be used to modify the circuit into a resonant converter circuit which has much improved efficiency.
The transformer action between the inductors inside that component gives a coupled inductor Ćuk converter with lower output ripple than a Ćuk converter using two independent discrete inductor components.
[6] A zeta converter is a non-isolated, non-inverting, buck-boost power supply topology.
[citation needed] A SEPIC converter is able to step-up or step-down the voltage.
