Evil little diode?

Starting point

Our customer had developed an automotive component that had failed in EMC tests. Locating the error was not a simple matter. A lack of manpower had hampered more intense troubleshooting. Preis Ing. performed the EMC examination.

Initial tests

We analyzed the behaviour of the electronic components in a variety of working environments and located a source of disturbance on the circuit board. A silicon diode in a switching regulator was exhibiting critical behaviour.

Finding a solution

The silicon diode was replaced by a Schottky diode to get closer to the threshold values. Nevertheless, at high operating temperatures, a leakage current appeared, leading to a thermal runaway. We therefore continued to search for a solution.

Further research and comparisons of Schottky diodes were conducted – the EMC limit was not achievable by merely replacing the diode.

The error shows up

The behaviour of the deficient component was increasingly examined in order to understand the principle of the disturbance effect.

Finallythe solution became clear: The layout of the circuit board was the source of the problem. The conductor tracks needed to be rearranged. Unfortunately, the customer was unable to implement the changes within a short amount of time.

A tangle of wires

However, we were able to help: We soon developed a proof of concept layout with manually wired connections on top of the PCB board. Using an optimized ground connection the seemingly tangled wires began to work more efficiently and did not exceed the threshold values.

The solution

In light of this new knowledge, we recommended a new layout to the customer. Some weeks later, we learned, that the EMC problem had been solved with new board generation.