Fet selection

Blog Entry 3 A more simple solution to implement is to use the 3478 Low-side N-channel controller in a SEPIC configuration. This application utilizes two inductors (instead of a Flyback transformer) to attain the Buck-Boost function. The 3478 requires an external user-selectable Fet switch, so you can choose the one that suits your load current requirement. The datasheet provides an application rationale for SEPIC configuration on page 19, Figure 13. The output voltage can be set to 12V by changing the value of the feedback resistor. 

Enzyme-immobilized FETs (ENFETs), 22 269. See also Enzyme ion-selective field-effect transistor (ENFET) Field effect transistors (FETs)... 

ISFETs), 3 799 9 585 74 24. See also Field effect transistors (FETs) Ion-selective membranes, cavities in, 9 584 Ion size, cluster glass transition and, 74 469, 470... 

These measure the potential difference between the transducing electrode and a reference electrode under conditions of zero current. Three types of potentiometric detectors are commonly employed ion-selective electrodes (ISE), gas-sensing electrodes and field effect transistors (FET). 

In ion-selective FETs (ISFETs), an ion-selective membrane replaces the gate electrode. When an enzyme-loaded gel is combined with the membrane, the device can be used to measure substrates which enzymically generate charged species. 

PhI02 is rather bulky and plugs the pores, thus preventing further access of reactants to the active sites [49-50,63-64]. Therefore turn-overs are quite low when PhIO is used as oxidant. For the oxidation of methyl cyclohexane on TMPcY [49-50,63-64] and of cyclohexane on Fet.BuPcY [67] turn-overs are 5.6 and 7.6 respectively. It should be noted that the reported turn-overs for oxidations with PhIO correspond to conversions of less than 1 substrate molecule per two supercages, or to total conversions of less than 0.1 %. Therefore the observed activities and selectivities may be influenced by sorption effects. Furthermore iodosobenzene is a rather expensive oxidant and not practical to use because of its low solubility in solvents. Therefore some researchers tend to use other oxidantia such as air [65,66] and tertiary butyl hydroperoxide (t-ButOOH) [57]. In the oxidation of n-octane with t-ButOOH turn-overs as high as 6000 have been reported [57]. 

Fig. 6.19 Evolution of ion-sensitive field-effect transistor (ISFET) from insulated gate FET and ion-selective electrode (ISE)...

The electrical current flows from the source, via the channel, to the drain. However, the channel resistance depends on the electric field perpendicular to the direction of the current and the potential difference over the gate oxide. Should this surface be in contact with an aqueous solution, any interactions between the silicon oxide gate and ions in solution will affect the gate potential. Therefore, the source-drain current is influenced by the potential at the Si02/aqueous solution interface. This results in a change in electron density within the inversion layer and a measurable change in the drain current. This means we have an ion-selective FET (an ISFET), since the drain current can be related to ion concentration. Usually these are operated in feedback mode, so that the drain current is kept constant and the change of potential compared to a reference electrode is measured. 

The enzyme-containing FET, called ENFET, is fabricated from an ISFET by casting a thin membrane containing the enzyme over an ion-selective membrane... 

Another approach is the use of the potentiometric principle with planar thin film electrodes on a separate chip but in close vicinity to a FET input amplifier. Glucose and urea chips are now on the market commercialized by the company i-stat. These sensors are based on ion selective electrodes. The problems of stability are circumvented by a simple on chip calibration procedure and by the use of such microelectronic electrodes as disposable single shot probes for measuring Na, K, Cl, BUN, Glucose,iCa,pH,pC02 and Hct [56,57]. 

As discussed earlier, semiconducting SWNTs are the ones useful in nanotube-based FET devices.63,75 With rare exceptions,76 however, as-produced SWNTs are mixtures of semiconducting and metallic nanotubes (in a ratio close to the statistical limit of 2 to l).77 Therefore, the selective removal of metallic SWNTs for purer... 

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