Determining the maximum allowable heatsink voltage to ensure compliance with a given radiated emissions specification

A model to estimate the minimum voltage between a heatsink and a PCB that is required to generate a given radiated electromagnetic field strength from a PCB with attached cables is introduced. The model is based on a previously introduced technique for calculating the maximum possible radiated field due to a known voltage driving a heatsink against a circuit board with attached cables. A closed-form expression is derived that can be used to determine if a measured voltage on a heatsink is capable of generating a field strong enough to exceed an FCC or CISPR radiated emissions limit.