Post LC-filter

Note that the very existence of the RHP zero in the boost and buck-boost can be traced back to the fact that these are the only topologies where an actual LC post-filter doesn t exist on the output. Though, by using the canonical modeling technique, we have managed to create an effective LC post filter, the fact that in reality there is a switch/diode connected between the actual L and C of the topology, is what is ultimately responsible for creating the RHP zero. 

Figure 4.10. On-line coupling of USAL and detection with derivatization (A) in the pre-column mode for the determination of coiistin A and B in feeds (B) in the post-column mode for the determination of N-methyicarbamates in soil and foods, AC — analytical column, C — carrier, DC — derivatization coil, EL — elution loop, F — filter, FD — fiuorimetric detector, HC — hydrolysis coil, HPiV — high-pressure injection valve, HPP — high-pressure pump, IV — injection valve, L — leachant, LC — leaching chamber, MP — mobile phase, OPA — o-phthaldiaidehyde, PC — preconcentration column, PL — propagating liquid, PP — peristaltic pump, S / — switching valve, UP — ultrasonic probe, W — waste and WB — water bath. (Reproduced with permission of Elsevier, Refs. [48,49].)...

In a buck, there is a post-LC filter present. Therefore this filter stage can easily be treated as a cascaded stage following the switch. The overall transfer function is then very easy to compute as per the rules mentioned in the previous section. However, when we come to the boost and buck-boost, we don t have a post-LC filter — there is a switch/diode connected between the two reactive components that alters the dynamics. However, it can be shown, that even the boost and buck-boost can be manipulated into a canonical model in which an effective post-LC filter appears at the output — thus making them as easy to treat as a buck. The only difference is that the original inductance L (of the boost and buck-boost) gets replaced by an equivalent (or effective) inductance equal to L/(l—D)2. The C remains the same in the canonical model. 

An equivalent post-LC filter stage, that takes in this output and converts it into the output rail of the converter... 

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