Additionally, the parasitic elements of the transformer, namely leakage inductance and magnetizing inductance can be used tuned to modify the circuit in to a resonant converter circuit which has much improved efficiency. However, the turns ratio can be controlled to reduce device stress on the input side. īecause the isolated Ćuk converter is isolated, the output-voltage polarity can be chosen freely.Īs 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. An AC transformer and an additional capacitor must be added. The Ćuk converter can be made in an isolated kind. The energy in an inductor is given by:Į = 1 2 L I 2 is the switching frequency. In steady state, the energy stored in the inductors has to remain the same at the beginning and at the end of a commutation cycle. However, unlike these converters, it can also operate in discontinuous voltage mode (the voltage across the capacitor drops to zero during the commutation cycle). Charging a capacitor with a current source (the inductor) prevents resistive current limiting and its associated energy loss.Īs with other converters ( buck converter, boost converter, buck–boost converter) the Ćuk converter can either operate in continuous or discontinuous current mode. 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. At a short time scale an inductor can be considered as a current source as it maintains a constant current. The two inductors L 1 and L 2 are used to convert respectively the input voltage source (V i) and the output voltage source (C o) into current sources. The capacitor C is used to transfer energy and 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). It is an inverting converter, so the output voltage is negative with respect to the input voltage. When in the on-state, the capacitor C transfers the energy to the output capacitor through the inductance L 2.Ī non-isolated Ćuk converter comprises two inductors, two capacitors, a switch (usually a transistor), and a diode. It can be seen that when in the off-state, the capacitor C is being charged by the input source through the inductor L 1.

In this figure, the diode and the switch are either replaced by a short circuit when they are on or by an open circuit when they are off. Fig 3: The two operating states of a non-isolated Ćuk converter.

The isolated cuk converter