Selection of the Filter Capacitor for Power Supplies using 1-Phase Diode Rectifier
Diode bridge rectifiers with capacitor-input filters are commonly used at the input stage for power supplies operating from the single phase mains input, as they provide a cost effective solution in the lower power range. However, as there is no simple design rule existing in published literature that gives a reasonable prediction based on real-life conditions, the design of the rectifier-capacitor stage is still a trial and error or based upon experience. This paper presents an approximate (but simple) solution based upon empirical relations, for the prediction of the currents involved and specifies the capacitor, so that it can be selected.
Analysis of Rectifier Operation
An analysis of rectifier operation in principal circuits is made. The introduction of linear equivalent diode resistance values permits a simplified and accurate treatment of circuits containing high-vacuum diodes and series resistance. The evaluation of these equivalent resistance values and a discussion of emission characteristics of oxide-coated cathodes precede the circuit analysis. Generalized curve families for three principal condenser-input circuits are given to permit the rapid solution of rectifier problems in practical circuits without inaccuracies due to idealizing assumptions. The data presented in this paper have been derived on the basis of a sinusoidal voltage source. It is apparent that the graphic analysis may be applied to circuits with nonsinusoidal voltage sources or intermittent pulse waves. It is also permissible to consider only the wave section during conduction time and alter the remaining wave form at will. Complicated wave shapes may thus be replaced in many cases by a substantially sinusoidal voltage of higher frequency and intermittent occurrence as indicated by shape and duration of the highest voltage peak. The applications of these principles have often explained large discrepancies from expected results as being caused by series or diode resistance and excessive peak-current demands. Practical experience over many years has proved the correctness and accuracy of the generalized characteristics of condenser-input circuits.
Urea removal strategies for dialysate regeneration in a wearable artificial kidney.
The availability of a wearable artificial kidney (WAK) that provides dialysis outside the hospital would be an important advancement for dialysis patients. The concept of a WAK is based on regeneration of a small volume of dialysate in a closed-loop. Removal of urea, the primary waste product of nitrogen metabolism, is the major challenge for the realization of a WAK since it is a molecule with low reactivity that is difficult to adsorb while it is the waste solute with the highest daily molar production. Currently, no efficient urea removal technology is available that allows for miniaturization of the WAK to a size and weight that is acceptable for patients to carry. Several urea removal strategies have been explored, including enzymatic hydrolysis by urease, electro-oxidation and sorbent systems. However, thus far, these methods have toxic side effects, limited removal capacity or slow removal kinetics. This review discusses different urea removal strategies for application in a wearable dialysis device, from both a chemical and a medical perspective.