Node voltage

Suppose that we have hidden a number of the branch currents, and we now wish to display one of the hidden currents. Displaying hidden branch currents is a little different than displaying hidden node voltages. Node voltages are... 

Geoelctic field variations are calculated for five geomagnetic severities (from minor to extreme) and six frequencies (10-5-1 Hz). The voltage difference over the branch is calculated by integrating the projected electric field across the path. Since all the HV equipment is grounded, the voltage node difference method is used for GIC determination. 

The eenter node of the resistor divider beeomes a eurrent summing node where a portion of the total sense eurrent eomes from eaeh of the sensed output voltages. The higher power output, and usually the output that requires a tighter output regulation, require the majority of sense eurrent. The lighter loaded... 

There is one node within each switching power supply that has the highest ac voltage compared to the others. This node is the ac node found at the drain (or collector) of the power switch. In nonisolated dc/dc converters, this node is also connected to the inductor and catch (or output) rectifier. In transformer-isolated topologies, there are as many ac nodes as there are windings on the transformer. Electrically, they still represent a common node, only reflected through the transformer. Special attention must be paid to each ac node separately. 

This node(s) presents a different problem. Its AC voltage can be easily capac-itively coupled into any adjacent traces on different metal layers, as well as radiate EMI. Unfortunately, it is generally the trace that must also act as a heatsink for both the power switch and the rectifiers, especially in surface mount power supplies. Electrically, the trace wants to be as small as possible, but thermally, it wants to be large. There is one good compromise in the surface mount designs, and that is to make the top PCB island identical to the bottom PCB island and connect them with numerous vias (or thru-hole connections). This can be seen in Figure 3-62. 

For the power switeh ae node, the voltage wants to be delayed on the turnoff transition. This provides loading of the magnetie element during the forward reeovery time of the output reetifler. For the output reetifler ae node, the eurrent wants to be delayed at its turn-off. This limits the refleeted eurrent spike eaused by the reverse reeovery period of the reetifler. These teehniques are shown in the following seetions. 

Thermal analysis is really no more diffieult than Ohm s Taw. There are similar parameters to voltage, resistanee, nodes, and branehes. For the majority of elee-tronie applieations, the thermal eireuit models are quite elementary and if enough is known of the thermal system, values ean be ealeulated in a matter of minutes. If one has a temperature-measuring probe, the thermal eomponents ean also easily be measured and ealeulated. 

Electronics has, in fact, been a very fertile area for SEM application. The energy distribution of the SEs produced by a material in the SEM has been shown to shift linearly with the local potential of the surface. This phenomenon allows the SEM to be used in a noncontact way to measure voltages on the surfaces of semiconductor devices. This is accomplished using energy analysis of the SEs and by direedy measuring these energy shifts. The measurements can be made very rapidly so that circuit waveforms at panicular internal circuit nodes can be determined accurately. 

---