Dear Cyril, Dear colleagues,

The capacitors stores the electrical energy in its electric field associated with its stored charges on the plates of the capacitor. So , the energy is stored in form of potential energy E= .5 CV^2. Drawing current i from the capacitor leads to decreasing of the initial voltage of the capacitor such that i=C dV/dt. Therefore to keep the voltage of the capacitor constant we have to charge the capacitor at the same time with an equal amount of the charge dQ=C dV. Otherwise, the voltage across the capacitor will decrease to zero.However assuming an ideal capacitor all the energy stored in the capacitor will be transferred to the load. This means that an ideal capacitor acts as voltage source with zero source resistance . Since practical capacitors are nearly ideal elements they are used at the output for DC power supplies in conjunction with voltage regulators or on their owns.

In summary, a charged ideal capacitor can act as an ideal voltage source.

On the other side, a charged inductor with a current i stores electric energy in its magnetic field. The energy stored E= ,5 Li^2. As argued with the capacitor if the charged inductor is ideal it can act as an ideal current source. Unfortunately,inductors are less ideal than the capacitors because their coil resistance is appreciable. So upon discharging the inductor part of the stored energy will be dissipated internally rendering charged inductors less ideal current source. In order to keep the inductor current constant to act as a current source we have to contiguously charge the inductor with an amount of the current withdrawn from it.

In conclusion, Charged capacitors and inductors can function as a voltage and current sources respectively with capacitors normally behaving more ideal.

Therefore capacitors are used intensively in constant voltage DC power supplies.

Thank you.

There is a starting problem with your question. The problem is there is no such thing as a pure capacitor or a pure inductor in reality to begin with :-)

100% correct Derek. Irrespective of whether a voltage or current source is used to represent energy stored in the EM fields it requires work / energy to establish them. Ideal would imply an infinite source of energy. Also such EM fields have to co-exist during their establishment.

Circuit components such as RLC are just human analogies used to represent energy stored in EM fields and heat dissipated in materials. It is a rather circuitous and trivial debate similar to the ideal switch argument.

However, by exploiting material properties and through controlled energy conversion we can get good approximations within well defined practical and physical limits.

There is a limit to which one may use and apply circuit component analogies.

I have not yet had time to study the thread "What is current source etc." which seems to be "parent" to this thread, but from scratch I would suggest that the overall discussion and argumentation, I think, goes slightly in a wrong way.

In the circuit theory, the "source" (voltage or current) is not introduced in the meaning of some "ultimate" source from the physical or philosophical point of view (like, for example, "Labour is the source of Wealth" or "Sun is the source of energy for mankind"). Instead, it is introduced solely with respect to the source's terminals, from which the circuit that is external to these terminals "acquires" voltage or current. If we speak, for example, about a "voltage source", it is a "VOLTAGE source", not a "voltage SOURCE" that is meant by this expression.

An ideal "voltage source" is simply an element providing voltage across its output that does not depend upon the current flowing, for the "current source" it is vice versa.

I think that the question of "purity" is altogether out of scope here, because all circuit elements considered in circuit theory are just models with regard to the actual practice - and that is evident. The fact that there is nothing ideal does not mean that the model itself is invalid.

I agree that capacitors and inductors with nonzero initial conditions can be considered voltage and current sources, respectively. Moreover, with a large time constant it may be not just a quirk, but actual practical behavior in a real circuit.

True sources like true points lines and planes are a concept not a realizable object. A capacitor or inductor are approximations of sources. If the capacitance or inductance was infinite, they would be true sources (at steady state) in that the voltage or current would never change no matter how much current was drawn. In reality, a battery is much closer to a voltage and current source than a capacity or inductor.

An ideal voltage source has zero output impedance, while an ideal current source has infinity output impedance. Since there is no ideal source in reality, a capacitor discharge process often keeps voltage nearly no abrupt change in comparison with its current, and its output impedance equal to dv/di is nearly zero. For an inductor discharge process, in contrast, the current has often no abrupt change while the voltage is not, and thus, it can be modeled as a current source, because dv/di goes to very large (but is not ideally going to infinity). The inductor discharge current source has already been widely used in many applications, such as to generate a current sawtooth waveform in a flyback transformer for high DC voltage generation, etc.

Dear Cyril, Dear colleagues,

The capacitors stores the electrical energy in its electric field associated with its stored charges on the plates of the capacitor. So , the energy is stored in form of potential energy E= .5 CV^2. Drawing current i from the capacitor leads to decreasing of the initial voltage of the capacitor such that i=C dV/dt. Therefore to keep the voltage of the capacitor constant we have to charge the capacitor at the same time with an equal amount of the charge dQ=C dV. Otherwise, the voltage across the capacitor will decrease to zero.However assuming an ideal capacitor all the energy stored in the capacitor will be transferred to the load. This means that an ideal capacitor acts as voltage source with zero source resistance . Since practical capacitors are nearly ideal elements they are used at the output for DC power supplies in conjunction with voltage regulators or on their owns.

In summary, a charged ideal capacitor can act as an ideal voltage source.

On the other side, a charged inductor with a current i stores electric energy in its magnetic field. The energy stored E= ,5 Li^2. As argued with the capacitor if the charged inductor is ideal it can act as an ideal current source. Unfortunately,inductors are less ideal than the capacitors because their coil resistance is appreciable. So upon discharging the inductor part of the stored energy will be dissipated internally rendering charged inductors less ideal current source. In order to keep the inductor current constant to act as a current source we have to contiguously charge the inductor with an amount of the current withdrawn from it.

In conclusion, Charged capacitors and inductors can function as a voltage and current sources respectively with capacitors normally behaving more ideal.

Therefore capacitors are used intensively in constant voltage DC power supplies.

Thank you.

Thank you, Abdelhalim for the comprehensive answer! Really, capacitors connected in parallel to the rectifier's output act exactly as supplementary voltage sources and inductors connected in series - as current sources. I marvel over if there is some difference between a charged capacitor and a battery; both they are continuosly exhausting sources...

Regards, Cyril

Voltage generate in capecitive circuit=Cdv/dt(C=dq/dv)variation of charge with voltage.

Voltage generate in Inductive circuit=Ldi/dt(L=do/di)variation of flux(do) with current.

So when any circuit (inductive)opens(made off)due to inducive effect of circuit voltage will produced at open end and spark will appear,can be suppresed by connecting capecitance across terminals, chargs capecitance , will discharged slowly and spark burning the contact can be avoided and is good example to understand the effect.

Practice we used to generate electricity in conductor needs to cut the flux(voltage induced in conductor is praposnal to rate of change of cutting of flux(do/dt) ),so more voltage can be generated by increasing speed or flux in generator.