Topologies quasi-resonant

Quasi-resonant converters force the voltage or current waveform into a haver-sine waveshape. If the power switch(es) are switched at the right moments, then there are no switching losses experienced. Also because of the controlled rates of change for the voltage or current waveforms, much better RFI/EMI performance is realized. Most of the basic topologies that exist within the PWM family are also in the quasi-resonant family. 

The zero current switching (ZCS) quasi-resonant (QR) switching power supply forces the current through the power switch to be sinusoidal. The transistor is always switched when the current through the power switch is zero. To understand the operation of a ZCS QR switching power supply, it is best to study in detail the operation of its most elementary topology—the ZCS QR buck converter (and its waveforms) as seen in Figure 4-10. 

ZVS QR topologies appear to be the more popular of two methods of quasi-resonant technologies. This is mainly due to two reasons first, its typical variation in frequency over its input and load variations is 4 f as opposed to fO f for the ZCS topologies secondly, it has a better heavy load performance. Also, some of the more troublesome parasitic elements within the circuit can be more easily harnessed. 

Quasi-resonant Switching Power Supply Topologies... 

As with PWM switching power supplies, there are comparable topologies within the zero-current switching (ZCS) and zero-voltage switching (ZVS) quasi-resonant families. You ll immediately recognize the family members upon seeing them. 

Figure 4-12 Nontransformer-isolated quasi-resonant topologies.

This design example is the PWM design example (Section 3.15.4), modified to a quasi-resonant topology. Please refer to Figure 4-25. 

In applications where high power density or thermal management is of prime importance, hard- switched converters are not feasible using conventional Si components. In these cases, resonant or quasi-resonant (also termed soft-switching ) topologies can be used. The electrical resonance is obtained through parasitic... 

The adiabatic passage induced by two delayed laser pulses, the well-known process of STIRAP [69], produces a population transfer in A systems (see Fig. 7a). The pump field couples the transition 1-2, and the Stokes field couples the transition 2-3. It is known that, with the initial population in state 11), a complete population transfer is achieved with delayed pulses, either (i) with a so-called counterintuitive temporal sequence (Stokes pulse before pump) for various detunings as identified in Refs. 73 and 74 or (ii) with two-photon resonant (or quasi-resonant) pulses but far from the one-photon resonance with the intermediate state 2), for any pulse sequence (demonstrated in the approximation of adiabatic elimination of the intermediate state [75]). Here we analyze the STIRAP process through the topology of the associated surfaces of eigenenergies as functions of the two field amplitudes. Our results are also valid for ladder and V systems. 

The topological analysis thus shows that with two quasi-resonant delayed lasers it is not possible to end in a superposition of states between the lowest states 1) and 13) in a robust way. We can remark that in Ref. 76, it has been shown that one can create such a superposition—however, in a nonrobust way but still by adiabatic passage, by modifying the end of the STIRAP process (with the counterintuitive sequence), maintaining a fixed ratio of Stokes and pump pulse amplitudes. 

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