Topology Tutorial_ Cuk Converter.txt

[MUSIC PLAYING] The Cuk converter itself is named by Slobodan Cuk. It's an inverting SEPIC. It's also a flyback typology. Means energy is transferred to the coupling cap once the switch is open. The benefit here is the LC filter is located at the input. And the other LC filter is located at the output. Means we have continuous currents at the input and the output, so ripple on both sides of the converter is very low. On the other hand, we got two double poles in our power stage that are reducing dynamic a bit. You need high gain in your [INAUDIBLE] amplifier to get a reasonable dynamic performance. And same for all those topologies, if the inductors are coupled, the windings ratio 1 by 1 is mandatory. A boost controller with a single driver, as well, low cost for your design. And also, you can do this with only one switch and only one rectifier, compared to the non-isolated inverting flyback. Again, clean waveforms, no ringing means low EMI, low radiated emissions. Multiple windings are possible because the output windings are well-coupled on the core. And, well, there is another small drawback. You got a negative output voltage, but your controller, in most cases, needs a positive feedback voltage. So you need an additional small, but cheap operational amplifier to turn the negative feedback voltage into a positive one. Now, we change the topology a bit from the SEPIC converter to the Cuk Converter, so an inverting SEPIC. Again, it's pretty close to a two-stage approach here. If the switch is open, steady state, you notice that across the winding of L1, C1 is charged left-handed by the input voltage, but right-handed by L2, also on the negative output voltage. So the major difference here is that the coupling capacitor C1 sees input voltage plus output voltage. That's your voltage stress at C1. At SEPIC, if you regard it the same, you will see that at C1 is only present the input voltage. And what we learned before is when Q1, the switch is closed, we got the magnetizing currents, the sum of the magnetizing currents of L1 and L2 across the switch. And if we opened a switch, we got the sum of the demagnetizing currents across the rectifier. Here we are. If we close the switch, the input voltage is present across L1, and output plus input voltage is present across L2. And if we open now the switch, the demagnetizing current is driven by L1 across C1, across the rectifier, back to the input capacitor. Same for the output, we got the demagnetizing current driven by L2 across the rectifier D1 to the output. The interesting thing here is if we look on the right side, the inductor current L1 and the inductor current L2 is continuous, so neither a pulse current at the input nor the output. This typology is well-suited for sensitive applications.