Loop currents

C3.2.4.3 INTERPRETING THE QUANTUM NATURE OF PROTEINS REDUCED HAMILTONIANS AND CURRENT LOOPS... 

Particle shape is also important. Disk-shaped as well as cylindrical-shaped conductors have a high response because large induced current loops are formed. Small randomly shaped conductors, such as those present in cmshed slag, also respond favorably. Sphere-shaped particles generate small-current loops, however, and do not have a high response. Multiple-current loops occur in conductors that have irregular bends, producing counteractive forces that tend to nullify each other. 

Electronic signals (that is, 4-20 milhamp current loops) are represented by dashed lines. In Fig. 8-47, these include the following ... 

In order for electronic transmission systems to be less susceptible to interference from magnetic fields, current is used for the transmission signal instead of voltage. The signal range is 4 to 20 miUiamps. In each circuit or current loop, there can be only one transmitter. There can be more than one receiver, but not an unlimited number. For each receiver, a 250 ohm range resistor is inserted into the current loop, which provides a 1- to 5-volt input to the receiving device. The number of receivers is hmited by the power available from the transmitter. 

High level. Where the source is a process transmitter, the range resistor in the current loop converts the 4-20 milliamp signal into a 1-5 volt signal. The conversion equipment can be unipolar (i.e., capable of processing only positive voltages). 

No signal integrity loss if current loop is used and signal is segregated from A.C. current. 

As one can notice, the boost-mode converter has the same parts as the forward-mode converter, but they have been rearranged. This new arrangement causes the converter to operate in a completely different fashion than the forward-mode converter. This time, when the power switch is turned on, a current loop is created that only includes the inductor, the power switch, and the input voltage source. The diode is reverse-biased during this period. The inductor s current waveform (Figure 3-4) is also a positive linear ramp and is described by... 

There are four current loops inside of every switching power supply. Each of these loops must be kept separate from one another. They are listed in order of their importance to a good PCB layout. 

Figure 3-59 The major current loops within the major switching power supply topology types (a) the nonisolated buck converter (h) the nonisolated boost converter (c) the transformer-isolated converter.

The power switch and rectifier ac-current loops contain very high trapezoidal current waveforms typical in PWM switching power supplies. These waveforms are rich in harmonics which extend far above the basic switching frequency. These ac currents can have peak amplitudes two to five times that of the... 

These ac current loops should be routed before any other traces in the power supply. The three major components that make up each loop the filter capacitor, the power switch or rectifier, and the inductor or transformer must be located adjacent to one another. The components must also be oriented such that the current path between them is as short as possible. A good example of a layout of the power section of a buck (or step-down) converter can be seen in Figure 3-60. 

The grounds represent the bottom branch of the current loops discussed earlier. Grounds, though, serve a very important function as the common point of reference for the circuitry. Therefore, grounds must be carefully placed in the layout. Intermingling these grounds will cause problems with the stability of the power supply. 

On a typical one-sided board (still very common in commercial AC-DC power supplies), as the number of capacitors you try to parallel goes up, so does the intervening PCB trace impedance. Take, for example, Figure 5-1, where we have the simple case of one output capacitor. A small advisory here—if you try to reduce the impedance further by making the current loop smaller and smaller, the capacitor would eventually start comparing notes with the heatsink on the topic of temperature, and that can t be good for its life expectancy. 

What if we place a small sense resistor instead of a current loop, to read the current through a capacitor Well, if we use a very small sense resistor, we will have so much relative noise, our readings would be unreliable. If we use a larger sense resistor, we would still divert current into other paralleled capacitors. Again, the correct solution is the same as for the current loop, measure all together, and then divide by the number of capacitors. 

A thoughtless cut in the Ground Plane can divert the return current away from its preferred path (underlying the forward trace), thereby increasing the area of the enclosed high-frequency current loop and therefore also the inductance... 

You have to follow the gray current loops that show how the Gate drive current flows. The lower Fet is in effect very close to the IC, because the ground plane cancels most of the... 

So in Figure 6-4, we do trace section analysis for a Forward converter, and find that there are two separate current loops we need to minimize here. The differences between Figure 6-4 and Figure 6-1 are subtle but important. The latter is in effect only one current loop, even though it spans both the input and output sections. 

Note that while prototyping, it is a bad idea to insert a current probe (through a loop of wire), anywhere in a critical trace section. The current loop becomes an additional inductance that can increase the amplitude of the noise spikes dramatically. Therefore practically speaking, it can often become virtually impossible to measure the switch current or the diode current individually (especially in the case of switcher ICs). In such cases, only the inductor current waveform can really be measured properly. Sometimes we can place a small sense resistor instead of a current loop, because a good resistor will not create inductive kicks at least. 

In a Flyback, the high-frequency current loop encloses the transformer secondary, the output diode, and the output capacitor. This loop must be minimized as far as possible. 

Figure 11-15 A High-voltage Decoupling Ceramic Capacitor Close to the Power Stage Helps Complete the Noise Current Loop...

The analyst may either 1) install a smaller loop on the injector, or 2) partially fill the current loop, using the syringe to measure the volume. 

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