This circuit is sometimes called a pie network because it is shaped like the Greek letter Pi (Π or π). There is an MOV across the input, a TVS across the output and an inductor is placed between them. The MOV is used to absorb the brunt of the surge energy coming into the circuit. It should be selected large enough to have a long life expectancy in the application. More exposed installations will require larger MOV devices. Sometimes several MOV devices should be placed in parallel to share the incoming surge. The inductor is used to coordinate the operation of the MOV and the TVS. At the peak of the surge, the voltage across the MOV will be divided across the inductor and the TVS. Choosing the correct inductor will assure the survival of the TVS during the surge. It is important to use only air core inductors in this application. Iron core inductors are more common and smaller in size. However, iron core inductors will saturate at currents well below the surge current. Saturation effectively reduces the inductor value and will leave the TVS vulnerable to damage. The TVS should be selected to achieve the low clamping voltage required. Some effort is usually required to determine the best TVS for the application. Choosing a small TVS will certainly keep costs in line, but will result in higher clamping voltages and a more expensive inductor. Carefully selecting these three components has been shown to be a very effective protection solution providing the benefits of the MOV and the TVS.