Reverse recovery

A small Schottky rectifier with a current rating of about 20 to 30 percent of the MOSFET current rating (/d) is placed in parallel with the MOSFET s intrinsic P-N diode. The parallel schottky diode is used to prevent the MOSFET s intrinsic P-N diode from conducting. If it were allowed to conduct, it would exhibit both a higher forward voltage drop and its reverse recovery characteristic. Both can degrade its efficiency of the supply by one to two percent. 

Saturable Inductors to Limit Rectifier Reverse Recovery Current... 

Figure 4-9 Typical use of saturable inductors in reducing reverse recovery losses.

One subtle, but major noise source is the output rectifier. The shape of the reverse recovery characteristic of the rectifiers has a direct affect on the noise generated within the supply. The abruptness or sharpness of the reverse recovery current waveform is often a major source of high-frequency noise. An abrupt recovery diode may need a snubber placed in parallel with it in order to lower its high-frequency spectral characteristics. A snubber will cost the designer in efficiency. Finding a soft recovery rectifier will definitely be an advantage in the design. 

The reversible recovery of a deformed elastomer to its original (undeformed) state is due to an entropic driving force. The entropy of polymer chains is minimum in the extended conformation and maximum in the random coil conformation. Cross-linking of an elastomer to form a network structure (IX) is... 

Another way of reducing the reverse recovery current shoot-through is simply to ensure that the boost diode is carrying no forward current at the moment when the switch starts to turn ON. The diode then blocks reverse voltage instantly. In other words, running the Boost in DCM or BCM (boundary conduction mode, i.e., at the critical boundary) will produce higher peak currents, but smaller inductors (yes, if r is large, the size of any inductor typically reduces ), and perhaps much better efficiency too, because now, the turn-on crossover loss becomes zero. 

Reverse recovery shoot-through current spike through Q1 occurs if during the preceding td (deadtime) interval the freewheeling current prefers to go through the body diode of Q2 instead of the paralleled Schottky... 

Incidentally, Schottky diodes do not have any reverse recovery current issues, but they do have some body capacitance, which can produce similar effects. However, that fear has always proven to be exaggerated. I have personally not seen any application having a performance issue explicitly related to a bad Schottky. The only exception was a case where the leakage current of the Schottky was so high, it was prematurely tripping the current comparators inside the switcher IC. And there was also a reliability issue once, concerning the dV/df rating of a commercial Schottky. Both these issues are discussed elsewhere in this book. 

LY294002 and wortmannin inhibit the enzyme PI-3 kinase required for the closure of pseudopodia to form intracellular vesicles (61,73-75,78,122). Compared to wortmannin, which is relatively unstable in aqueous media, the inhibitory effects of LY294002 are more specific, reversible (recovery after 10 minutes), and not light dependent. Therefore, LY294002 can be used for time-lapse experiments. Several studies have indicated that both substances have little or no effect on the other pathways described (75). However, both substances might block the uptake of Tfn as well (76). 

Williams, Landel, and Ferry equation (WLF) Used for predicting viscoelastic properties at temperatures above Tg when these properties are known for one specific temperature, yield point Point on a stress-strain curve below which there is reversible recovery. 

When the next switch in the timing sequence is turned on, it must conduct the reverse-recovery current of the diode. As in the case of dc-dc converters, the diode reverse-recovery process usually causes large current to flow, not only because reverse-recovery times can last hundreds of nanoseconds, but also because of the low-inductance power planes. Figure 3.14 shows the reverse-recovery characteristics of a silicon fast-recovery epitaxial diode (FRED) and a SiC diode. It is clear from this figure that the SiC diode is a far more capable replacement for the typical Si diode due to the lack of recovery current. 

Hall effect measurements indicate mobilities of— 10-1 cm2 V-Isec-1 for both electrons (Dresner, 1980) and holes (E>resner, 1983). Tiedje et al. (1981) have measured drift mobilities of 1 cm2 V-1 for electrons and 10-3 cm2 V-1 sec-1 for holes. However, Silver et al. (1982) have estimated that the electron mobility is s 100 cm2 V-1 sec-1 by using the reverse recovery technique. 

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