The Time-sharing Principle

we have an important principle to understand, what I call the principle of time sharing. To understand it, we will need to start by applying it only to DC-DC converters at 

Buf a lOV/lA converter wifh a higher loss of, say, 0.7W, has in facf a better efficiency (10/10.7 = 93.5%), despife fhe load current being unchanged. It can all get very confusing. 

What happens if Vsw Vd In fact that is the situation in most commercial Flybacks. But note that to do a proper comparison, you have to reflect the diode drop to the primary side. And for that we have to multiply the diode drop by the turns ratio (see the equivalent Buck-Boost models of a Flyback section in my book. Switching Power Supply Design Optimization). So, for example, if the turns ratio is 20 and the diode drop is 0.6V, the effective Vd we need to compare with Vsw for our time-sharing analysis is 0.6 x 20 = 12V. And that is usually greater than the (average) drop across the switch. Therefore, we tend to say that in a Ryback, decreasing D (increasing input) will worsen the total conduction loss and decrease the efficiency. But of course that never happens, because as we increase the 

In all cases, in any topology, irrespective of Vsw and Vd, as we increase the input voltage sufficiently, the switching losses will ultimately start predominating and the efficiency will roll off. 

But we may succeed in pushing this roll-off point further and further away by reducing switch transition times. 

---

By the time-sharing principle, we see that in a Buck converter if Vsw is close to VD, the conduction losses do not change with duty cycle or input voltage. But the switching losses progressively increase, and so the efficiency falls off smoothly (almost linearly) with increasing input. See Figure 10-7 for the curve marked Vsw = VD. An example of this is the... 

A second important aspect of most microscopic theories of electron transfer is the assumption that the reactants and products do not change their configurations during the actual act of transfer. This idea is based essentially on the Franck-Condon principle, which says, in part, that nuclear momenta and positions do not change on the time scale of electronic transitions. Thus, the reactant and product, O and R, share a common nuclear configuration at the moment of transfer. 

For clusters of higher nuclearity too, the kinetics method for determining the redox potential E°(M /M ) is based on the electron transfer, for example, from mild reductants of known potential which are used as reference systems, towards charged clusters M/. Note that the redox potential differs from the microelectrode potential E° (M. M /M ) by the adsorption energy of M onM (except for n = 1). The principle (Figure 5) is to observe at which step n of the cascade of coalescence reactions (14), a reaction of electron transfer, occurring between a donor S and the cluster M/ could compete with (14). Indeed n is known from the time elapsed from the end of the pulse and the start of coalescence. The donor S is produced by the same pulse as the atoms M", the radiolytic radicals being shared between M (reactions 1,7,8) and S (reactions 25, 26). 

---