Designing for reliability in high voltage applications

Designing and building a high voltage power supply that survives for years beyond that is an exacting art. Here are six pitfalls that high calibre power supplies are designed to avoid.

1. Poorly chosen insulation

To achieve reliability, you need to account for the thermal cycling that can occur in a power supply. Temperature changes can damage insulation materials. These materials need to be compatible, with similar thermal expansion coefficients and resistance to mechanical stresses.

2. Casual treatment of insulation

Poor adhesion, age-induced brittleness due to loss of plasticizers, excessive temperature swings, exposure to UV radiation, corona, ozone, mineral oil and harsh PWB cleaners and solvents can lead to premature failure due to insulation damage. The damage could happen during manufacturing or in subsequent operation.

3. Leakage currents

The combination of material properties, environmental factors and product design can create unplanned side effects. Leakage currents may increase over time: eventually, this can result in a hard-arc and catastrophic failure. Excessive leakage currents may create errors in high impedance feedback circuits, causing voltage drift and stability issues over time and with changes in temperature.

4. Moisture absorption

FR4 PWB substrates can be particularly vulnerable to contamination and absorbed moisture, which lowers the glass-transition temperature (Tg) of FR4. This can make the assembly susceptible to failure in dynamic thermal conditions.

5. Manufacturing process errors

Impurities, incorrect fillers, or incomplete cure in encapsulation systems can cause excessively high leakage currents that are non-linear and erratic over time and temperature, potentially destabilizing the high voltage system. High voltage circuits are particularly vulnerable to electrochemical migration.

6. Filament and dendrite formation

Moisture can lead to ionic corrosion, forming conductive filaments. Dendrite growth may occur from the redistributed metal ions. High voltage stresses accelerate these electro-chemical processes (though tin whiskers can form without the presence of an electromagnetic field). Crystalline microstructures created by ionic migration create very high voltage gradients and electric field intensities, which may lead to premature breakdown between voltage nodes.

For trusted, long-lasting performance in critical applications, make sure your high voltage power supplies are designed and built for smooth and reliable operation even under harsh operating conditions.

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