Pulse-skip

This chaotic mode is also a variable frequency mode of virtually unpredictable frequency spectrum and therefore unpredictable EMI and noise characteristics too. That is why fixed-frequency operation is usually preferred in commercial applications. And fixed frequency basically means no pulse-skipping ... 

A pulse-skipping mode, if properly implemented, will clearly improve the light-load efficiency. 

Question 51 How can we implement controlled pulse-skipping in a synchronous buck topology, to further improve the efficiency at light loads ... 

My suggestion is to open the pdf datasheet of any prospective switcher IC and carry out a text search (Ctrl + F) for the world foldback. If you find it, question the vendor about its full impact before you select the part for your application. Foldback is, in general, a good idea in terms of protecting the converter under abnormal conditions, but it should be used very judiciously so as not to impact normal behavior. For example, the Simple Switcher family has a hidden second-level current limit protection at which frequency foldback (or skipped pulses) occurs. But that trip level can only be encountered under very severe conditions—namely, a sudden overload with a completely incorrectly sized inductor that hard-saturates in the process. At other times it is not encountered and doesn t therefore interfere. It is considered transparent to all but the most novice engineers. And that is what I consider the right type of foldback. 

Let Te be the period of the excitation pulses, and TR be the ideal sampling time required to collect Np points per period. Let Ts be the sampling time performed by the instrument and Nw the number of waveforms skipped before the next point is sampled. From Figure 9.11 we have... 

Throughout this chapter it is assumed that the intensity of the polarized exciting pulse is sufficiently low that only a small fraction of the fluorophores are ever excited.(29) High light intensities are treated elsewhere/73 74) The following subsection presents some very general and basic theory that is not specifically directed toward rotational relaxation of DNA. The reader may wish to skip directly to the final result in Eq. (4.15), or even skip this subsection entirely. 

The second hardware unit was an interrupt, skip-check control unit for the Reticon arrays. This unit allows the computer to see the end-of-scan and beginning-of-scan pulses generated by the arrays and allows the computer to have an on/off control of the external clock which is used to start the analog to digital converter. 

Further, at very light loads we may want to be able to skip pulses altogether, so as to maximize efficiency (since switching losses go down whenever we skip pulses). But with high-side current sensing we are almost forced into turning the high-side mosfet ON every cycle — just to sense the current ... 

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