Input bridge

But how different can the Vl and Vn scans be In fact, the above two equations have inspired a rather misleading statement often found in related literature — if the noise emission is predominantly DM, the Vl and Vn scans will look almost the same. The scans also look identical if the noise is predominantly CM. And if the Vl and Vn scans look very different, that implies that both CM and DM emissions are present. However, in the case of an off-line power supply, this statement is clearly not true. Because, that would imply that somehow the emissions on the L and N lines are different. However, we know that in any typical off-line power supply (with an input bridge rectifier), the L and N lines are... 

Note that input bridge packs using ultrafast diodes are often peddled as offering... 

Line to line capacitors are called X-capacitors ( X-caps ). X-caps when used in off-line applications before the input bridge must be safety approved. But after the bridge (on the rectified side), it s basically a don t care situation from the safety point of view. Note that since it is essentially a front-end component, approved X-caps are typically impulse-tested up to 2.5 kV peak. 

The two models flip-flop back and forth at twice the line frequency. This could make it very hard to analyze. However, it has been seen that if a small X-cap is placed immediately to the left of the input bridge, then we can safely assume that the EMI spectrum is dominated by the voltage source, and can thus ignore the current source model. See Cl in Figure 10-1. 

Diodes are a potent source of low- to high-frequency noise. Slow diodes (like those in a typical input bridge) can also contribute to such noise. 

Input bridges that use ultrafast diodes are available, and their vendors claim significant reduction in EMI. But in practice they don t seem to provide much advantage. They also typically have much lower input surge current ratings. In fact... 

In a typical off-line input stage, with no Power Factor Correction ( PFC ) stage present, the input bridge conducts only for part of every ac half-cycle as seen from Figure 13-1. 

These bridge wire devices are relatively safe from initiation by direct application of heat and external mechanical influences or from most electrical inputs. They are designed for highly specialized electrical impulses (Ref 13)... 

Any Buck-derived topology (e.g., the Forward converter, the Half-Bridge, the Push-Pull, the Full-Bridge, etc.) needs an output choke. Otherwise it is akin to running a Buck without its inductor—you can thereby create a dead short cross the input supply rails. 

Fig. 15 A molecular OR gate, whose chemical structure maps the electrical circuit diagram shown in Fig. 20a. Two Aviram-Ratner molecular rectifier chemical groups have been bonded to a central chemical node. This intramolecular circuit with one simple node can be easily designed, because the node Kirchoff node law is valid here. Note that the molecular orbital of each partner can be still identified on the 2 T(E) because of their weak interactions through the CH2 bridge. This is not always the case. The obtained logic surface demonstrates an OR function for well-selected values of the input voltage, but with two logical level 1 outputs which would have to be corrected using an additional output circuit...

Figure 3.32 Input current waveform to the bridge rectifier. Simulations performed by William Hall, SatCon Applied Technologies, Linthicum, Maryland.

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