A series regulator has a pass element (Transistor) that is in series with the load. A shunt regulator has a regulating element (Zener diode or transistor) in parallel with the load.
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The series regulator is much more efficient at load currents less than maximum, because its dissipation is zero when the load current is zero. The shunt regulator, on the other hand simply distributes a constant power between the shunt regulator element and the load. If the load current is zero, the shunt regulator power is high. As the load current is increased mor power is dissipated by the load, and less pwer is dissipate by the shunt element. At full load, the efficiencies are about the same.
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I don't understand your question about total resistance.
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Skin effect is the tendency for current to be "crowded" toward the outside of a conductor at high frequencies. This increases the effective resistance of the conductor. Skin effect is negligible for frequencies below about 100 KHz.
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There are 2 types of core loss:
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Hysteresis loss is caused by the coercivity of the core material. As current is decreased to zero, the magnetic field does not go to zero. It therefore requires some energy to restore the field to zero as the current is reversed. Hysteresis losses vary As B^n, where B is the flux density, and n is a constant that varies with the core material. For silicon steel, n is apporoximately 1.6.
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Eddy Current losses arise because the core material is a conductor, and therefore has induced current flow due to the magnetic field. Eddy current losses are reduced by using insulated laminations in the core, rather than solid core material. Other materials, such as ferrites are inherently insulators, so laminations are not necessary. Eddy current losses vary as the square of B (flux density) and the square of V (Voltage).