Understanding the Inductor

In power conversion, we may have noticed that we always talk rather instinctively of voltage rails. That is why we also have dc-dc voltage converters forming the subject of this book. But why not current rails, or current converters for example  

We may have also observed that capacitors have a rather more direct relationship with voltage, rather than current. So C = Q/V, where C is the capacitance, Q is the charge on either plate of the capacitor, and V is the voltage across it. This gives capacitors a somewhat imperceptible, but natural association with our more comfortable world of voltages. 

It s perhaps no wonder we tend to understand their behavior so readily. 

Note that here we are using a mechanical switch for the sake of simplicity, thus also assuming it has none of the parasitics we talked about earlier. At time t = 0, we close the switch (ON), and thus apply the dc voltage supply (Vin) across the capacitor (C) through the small series limiting resistor (R). What happens  

This is actually quite encouraging, as it seems we have, after all, heard of the duality principle. In simple terms this principle says that a capacitor can be considered as an inverse (or mirror ) of an inductor, because the voltage-current equations of the two devices can be transformed into one another by exchanging the voltage and current terms. So, in essence, capacitors are analogous to inductors, and voltage to current. 

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