Electronic load circuits

The second alternative is an electronic load. This device is a circuit that has a controllable switch (typically a Darlington configured pair of bipolar transistors or a MOSFET) that can be modulated to conduct any level of current the user desires. An example of an electronic load circuit is presented in this chapter. The electronic load will be constructed piece by piece and tested separately. When all the pieces are constructed and simulated, the whole sum of the electronic load can be assembled and tested as a unit. 

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Question 9 Is there some interaction with nearby circuitry Yes, you could be picking up fields from nearby circuits, but that shouldn t affect a typical switcher, simply because it produces enough noise and fields of its own. However, it is a good idea to do the reverse-peel here. If I find the converter is on a larger system board, I immediately and carefully first cut off all the traces leading from its output and divert them to my predictable electronic load. I also cut the input traces and divert them to my bench power supply. If the problem is gone, it is an interaction problem. 

One inconvenience associated with using operational amplifiers is the dual positive and negative power supplies that are frequently required. For convenience, and to limit the power source of our electronic load box to one power supply, we will include the following circuit in our electronic load. The circuit takes a 15 V DC signal and converts it to a -11 V DC signal. The schematic for this circuit is shown in Fig. 5.9. Note that the values shown are actual lab values of circuit. Standard resistor values are shown in parentheses. 

The final piece in the MOSFET electronic load puzzle is a method of adjusting the current limit. A simplistic yet flexible circuit to accomplish this is shown in Fig. 5.14. 

The breadboard pulse load waveform (from 300 mA to 5 A) is shown in Fig. 5.16. The IsSpice simulation results are shown in Fig. 5.17. Micro-Cap and PSpice results are shown in Figs. 5.18 and 5.19. In Figs. 5.15, 5.16, 5.17, and 5.19, the top waveform is the output of the comparator and the bottom waveform is the output of the analog switch (which would then be connected to the electronic load power circuit, such as that shown earlier in this chapter.)... 

A Li-ion battery usually consists of a composite cathode, a separator and an anode. The outer ends of the batteries are connected to a current collector that channels the electrons produced out to the load circuit. 

A typical rechargeable battery based on this idea has been constructed. It uses the [Ni(TTL)]a, polymer as the anode, poly-2-vinyl-pyridine-iodine (P2VP (x/2)l2) (68) complex as the cathode, and aqueous KI solution as the electrolyte solution (Equation 13). In the discharging process, electrons flow from the anode [Ni(TTL)]a to the cathode P2VP (x/2)l2 through the load circuit the iodide (or polyiodide) ions formed at the cathode then enter the electrolyte while an equivalent amount of iodide ions from the electrolyte solution intercalate into the oxidized metal tetrathiolene polymer (anode). The electrolyte concentration is therefore conserved. Upon recharging with an opposite... 

The force measuring head, together with provision for applying the extra compression. can be a beam balance, as used in the well-known Lucas apparatu.s. a universal tensile machine, or a specially designed electronic load cell unit [4]. The point at which the small amount of extra compression has been applied can be detected by breaking an electrical circuit. An early apparatus used a load cell attached to an arbor pre,ss. The operator manually lowered the pre.ss until the break in the electrical circuit was indicated visually by the extinction of a light. The Lucas apparatus has a similar detection system the balance weights are adjusted manually until the force exerted by the beam just overcomes the force exerted by the test piece. Both of these approaches involve a somewhat... 

Isolated A power electronic circuit which has ohmic isolation between the input source and the load circuit. 

When RCDs are in series in a circuit and operation discrimination is required, it is usually necessary to provide a greater time delay on the supply side device. Where there are electronic loads which distort the supply waveform with d.c. components, RCDs should be selected which are designed to suit. Regulation 537-02-03 forbids the use of semiconductor devices for isolation as the circuit controlled remains live in the off position. 

Figure 2.64. Electronic control circuits with operational amplifiers. Left stabilization of a current flowing through a load (e.g. a LED). Right potentiostat for control of electrolysis potential...

The flux of matter through a fuel cell or electrolyser is limited by the electrolyte (ionic) resistance, the electrode kinetics, and the external electronic load resistance. We commonly express the steady state situation and the fact that the current is the same through the entire closed circuit in terms of the voltage drops around the circuit ... 

Examination of the electrical parameters indicates that smaller separation between the electrodes reduces both the battery length and its volume or size. The space between the electrodes is filled with the electrolyte, which has two functions to provide a conduction path for ions, which for a Li-ion battery is Li+, and to impose a high resistance to electrons. Electrons are forced to flow in the external load circuit or to a device connected across the battery. 

In an electrical system such as in an electrochemical fuel cell, the electrical work is done as a result of the flow of electron across the system boundary through an electrical load circuit under the effect of an electromagnetic potential difference. When N electrical charges flow through an external load circuit owing to the electromagnetic potential difference E, electrical work is given as... 

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