The observers could adjust the crank and find the minimum or null at a particular setting. Cuk back in the 1970s had a mechanism to adjust the coupling of L1 & L2 using a crank with both the input and output currents visible on a scope. It's interesting that the switch S1 switches for both the boost and the buck sections at the same time when it's closed and when it's open, it allows C1 to be charged up, ready for the next cycle.Ī very fascinating thing about the Cuk converter is that both the input current ripple and the output current ripple can be reduced to zero by coupling the two inductors, L1 and L2. The buck's output is across smoothing cap C2. For the buck section, once S1 is off and the cap is no longer grounded, L2's current continues to flow thru diode D. When switch S is on, the left-side of cap C1 is grounded, so it becomes a switched voltage source to feed inductor, L2. Note that the cap takes the place of the series switch and input voltage in the Cuk's buck converter section. At that time, the voltage across L1 reverses such that it's in series aiding with the input voltage Vs and the two voltages add for the boost. When switch S is on (closed), inductor L1 charges up with current until S opens. The boost converter section operation is fairly straightforward. The first section, up to the series cap C1, is the boost converter and the second section that includes the cap, is the buck converter. Please refer to the circuit diagram, below. There are both non-isolated and isolated versions of this topology. The main disadvantages are that the output voltage is inverted in the non-isolated version, and that the switch current stress can be high. The energy flow is continuous, minimizing EMI, and the power can flow bidirectionally.

It has inherent EMI filtering of both the input and the output due to its topology, and the energy is transferred by a series cap, therefore, there's no danger of the series switch shorting the input to the output as with a buck converter (unless the cap shorts). The output voltage can be either lower or higher than the input voltage. It's a cascade of a boost converter with a buck converter and has only one gated switch (usually a MOSFET) and a diode. Slobodan Cuk of Caltech, is called an Optimum Topology Converter and has a zero input ripple and zero output ripple characteristic. The Cuk converter, invented in about 1977 by Dr.

Advantages of cuk converter