Series resonant (also known as series resonant voltage withstand device)circuit resonator is a circuit that includes connected inductor coils and capacitors. In such a circuit, current (and voltage) resonance can be excited. A resonant circuit is the simplest system in which free electromagnetic resonance may occur. Charge the capacitor with a capacitance of C to a voltage of U0. The energy stored in the capacitor is

When a capacitor is connected to an inductor, current I will flow in the circuit, which will cause self induced electromotive force (EMF) in the coil, with the aim of reducing the current in the circuit. The current caused by this EMF (in the absence of inductive losses) will be equal to the discharge current of the capacitor at the initial moment, which means the resulting current will be zero. At this (initial) moment, the magnetic energy of the coil is zero. Then, the current generated in the circuit will increase, and the energy from the capacitor will enter the coil until the capacitor is completely discharged. At this point, the electrical energy of theseries resonantcircuit E C=0. On the contrary, the magnetic energy concentrated in the coil is maximum and equal to, where L is the inductance of the coil and I0 is the maximum current value. Afterwards, the capacitor will start charging, that is, the capacitor will be charged with voltages of different polarities. Charging will continue until the magnetic energy of the coil enters the electrical energy of the capacitor. In this case, the capacitor will be charged again to the voltage of U0. As a result, resonance occurs in the circuit, and its duration will be inversely proportional to the energy loss in the circuit.