Power MOSFET Avalanche Guideline:The Power MOSFET is a very popular switching device used in switching power supplies and DC-DC converters. Their operation frequency is being continuously increased to reduce size and increase power density. This causes high di/dt, intensifies the negative effect from parasitic inductances, and results in high voltage spike between the Power MOSFET drain and source during device turn off. The spike is worst at power on due to empty bulk capacitors and small inductance because the transformer primary side inductance almost reaches the level of leakage inductance. Fortunately, the Power MOSFET is equipped to withstand a certain level of stress, unnecessitating expensive protection circuits. This note presents an effective way to determine the applicability of a Power MOSFET in an application. The designers can balance between cost and reliability.