Conduction loss

In contrast to triaxial porcelains, packaging materials such as 99% AI2O2 prepared by a soHd-state sintering process, display significantly lower dielectric loss. In these materials, there is no residual glassy phase with its associated mobile ion content, and therefore, conduction losses are minimized. 

First, the designer should choose the type of rectification technology that is most appropriate for the application. The choice is whether to use passive rectification in which semiconductor rectifiers are used or synchronous recification in which power MOSFE B are placed in parallel with a smaller passive rectifier. Synchronous rectifiers are typically used in battery operated portable products where the added efficiency, usually an added two to eight percent, is important to extend the operating life of the battery or in applications where heat is important. In today s switching power supplies, passive rectifiers can dissipate 40 to 60 percent of the total losses within the power supply. Synchronous rectifiers affect only the conduction loss, which can be reduced by as much as 90 percent. 

Id. For flyback-mode converters it is a good idea to select a power switch average current rating of about 1.5 times the maximum average input current of the supply. Another consideration is the loss. By overspecifying the current the /2i DS(on) loss (conduction loss) can be reduced with very little penalty on cost and input capacitance. 

The power switch is one of two of the most prominent sources for loss within the typical switching power supply. The losses basically fall into two categories conduction losses and switching losses. The conduction loss is where the power switch is in the ON state after the drive and switching waveforms have stabilized. Switching losses occur when the power switch has been driven into a new state of operation. The drive and switched waveforms are in a state of transition. These periods and their typical waveforms can be viewed in Figure 4-1. 

The conduction loss ( 2) is measured as the product of the switch terminal voltage and current waveforms. These waveforms are typically quite linear and the power loss during this period is given in Equation 4.1. 

This results in watts for the loss seen only during the turn-on transitions of the power switch. One would add the turn-off and conduction loss to this amount to arrive at the total loss within the power switch. 

The losses can once again be broken into three periods the turn-on loss, the conduction loss, and the turn-off loss. 

As seen in Section 4.1, the major types of losses are the conduction and switching losses. Conduction losses are addressed by selecting a better power switch or rectifier with a lower conduction voltage. The synchronous rectifier can be used to reduce the conduction loss of a rectifier, but it can only be used for forward-mode topologies, and excludes the discontinuous boost-mode converters. The synchronous rectifier will improve the efficiency of a power supply about one to six percent depending upon the average operating duty cycle of the supply. For further improvements, other techniques must be pursued. 

We can use the MTP4N50E, but the MTP8N50E will result in lower conduction losses. 

What happens if Vsw < VD In fact that is the situation in most commercial Flybacks. But note that to do a proper comparison, you have to reflect the diode drop to the primary side. And for that we have to multiply the diode drop by the turns ratio (see the equivalent Buck-Boost models of a Flyback section in my book, Switching Power Supply Design Optimization). So, for example, if the turns ratio is 20 and the diode drop is 0.6V, the effective VD we need to compare with Vsw for our time-sharing analysis is 0.6 x 20 = 12V. And that is usually greater than the (average) drop across the switch. Therefore, we tend to say that in a Flyback, decreasing D (increasing input) will worsen the total conduction loss and decrease the efficiency. But of course that never happens, because as we increase the... 

By the time-sharing principle, we see that in a Buck converter if Vsw is close to VD, the conduction losses do not change with duty cycle or input voltage. But the switching losses progressively increase, and so the efficiency falls off smoothly (almost linearly) with increasing input. See Figure 10-7 for the curve marked Vsw = VD. An example of this is the... 

Estimating the Ratio of Conduction Loss to Switching Loss... 

We analyze this in Figure 10-10, and the steps should be fairly obvious. Basically, we are writing the loss at each point as the sum of the switch conduction loss, the diode conduction loss, and a generic switching loss (crossover) term. We thus arrive at the general solution to the equations. We then take the published efficiency curves for the 2593HV (see... 

Because conduction losses are high for carbon black powder it can be used as lossy impurities or additives to induce losses within solids for which dielectric losses are too small. 

Consequences of the thermal changes of the dielectric permittivity 1 Conduction losses 13 Magnetic losses 13... 

The size of this iris determines the refiection coefficient of the cavity. The iris size needed for zero reflection coefficient, i.e., a matched cavity, depends on the dielectric and conductivity losses of the sample in the cavity and is adjusted by means of a post which partially extends across the iris. By adjustment of the position of this post, the cavity can generally be matched to the bridge. By means of the slide screw tuner of Fig. 21, the bridge is slightly unbalanced as in the rf circuitry of NMR. EPR absorption is then observed in ways similar to NMR by display of the EPR line on a CRO or by rectification of the AC components and display of the first derivative of the EPR signal on a graphic recorder. 

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