Capacitance charging time

Next the junction capacitance charging time is the time required to change the voltage across the junction capacitance due to current flow through the bulk semiconductor regions (an RC time constant) and is given by ... 

The most commonly used waveform for in vivo voltammetric measurements is square-wave. This involves the application of a potential pulse to the working electrode for a fixed time at fixed intervals. The current is measurai at the end of the potential pulse to minimize capacitive charging current contributions. This waveform is shown in Fig. 15 A. 

Basic electrostatic relationships are used to understand and investigate the sample situations. These relationships may include field strengths produced by static charges, electrostatic potential, capacitance, relaxation times, currents and potentials in flow systems, and many more. 

In these experiments, Au(lll) electrode was immersed in 0.1 M KOH solutions with 10 pM, 100 pM and 1 mM CioSH and kept at the constant potential of -FO.l V for a certain time. After that, the potential was scanned to more negative values in order to record the cathodic peak current. These and other experiments have proved that the saturated coverage is obtained after a sufficiently long holding time. The same applies to the cathodic peak potential also. Sumi and Uosald [125] have found that the maximum reaction charge is equal to 103 ( 5%) pC cm . Two components contribute to the measured total charge the first is produced in reaction (1), and the second is the capacitance charge... 

As an example, consider line A of Table 9.1 for the timescale of the cell charging time due to so called double-layer capacitance. As discussed later in this chapter, effective capacitance values are on the order of 1 Farad m-2. If current densities of a cell are on the order of 1.0 A cm-2, and representative over-potentials at the triple-... 

The DLCs can handle more than 500,000 charging/discharging cycles during a minimum operating life of 10 years with almost no change in their capacitance. Thanks to DLC, maintenance cycles and test runs are completely obviated. In addition, DLCs can be completely discharged, a condition which usually is inconceivable in conventional systems. Care must be taken to ensure short charging times in case of frequent power failures particularly in the UPS sector. In this point too, DLCs are far superior to conventional batteries. 

After application of a potential step of magnitude = 2 - Ei, the exponential decay of the current with time depends on the double-layer capacitance (Cd) and the solution resistance (Rs) (-> resistance, subentry - solution resistance), i.e., on the time constant r = RsCd- Consequently, if we assume that Cd is constant and the capacitor is initially uncharged (Q = 0 at t = 0), for the capacitive charge (Qc) we obtain... 

For example, in a typical SXGA (1280 x 1024) AMLCD, the refresh rate is 60 Hz, the frame time is 16.7 msec, and the line time is 16.3 psec. For 6-bit resolution, the RC charging time constant must be less than 3.3 psec. The total pixel capacitance is about 0.5 pF, so the TFT on-resistance must be less than 6.6 Mil. From liquation... 

PDEIS is a new technique based on fast measurements of the interfacial impedance with the virtual instruments [3] that benefits from the efficient synchronization of direct hardware control and data processing in the real-time data acquisition and control [4], The built-in EEC fitting engine of the virtual spectrometer divided the total electrochemical response into its constituents those result from different processes. Thus, just in the electrochemical experiment, we come from the mountains of raw data to the characteristics of the constituent processes - the potential dependencies of the electric double layer capacitance, charge transfer resistance, impedance of diffusion, adsorption, etc. The power of this approach results from different frequency and potential dependencies of the constituent responses. Because of the uniqueness of each UPD system and complex electrochemical response dependence on the frequency and electrode potential, the transition from the PDEIS spectrum (Nyquist or Bode plot expanded to the 3D plot... 

A possible source of error, only significant for the measurement of extremely high values of volume resistivity (> lO fim) using older instruments, arises from the self capacitance of the (electrode + specimen) system. If the charging time constant of this through the input resistance of the current meter is comparable with the measurement time for the resistivity, very large errors may be caused. 

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