CEO, Digital Power Systems
Introduction
Virtually no electronic circuit works without capacitors. They store electrical energy and can deliver significant amounts of energy in short bursts. However, capacitors age over time, which affects the lifetime of electronic devices such as power supplies.
Electrolytic Capacitors
Electrolytic capacitors can store large amounts of energy but have the shortest lifetime of all capacitor types. Long-life variants achieve 10,000 hours at 105 °C. Lifetime is highly temperature-dependent - according to the Arrhenius law, lifetime approximately doubles for every 10 °C reduction in temperature.
Tantalum Capacitors
Tantalum capacitors use tantalum oxide as a dielectric. Beyond technical aspects, there is an ethical concern: the raw material coltan is partly mined under problematic conditions in Africa, including child labour. There are also reports of spontaneous fires on PCBs.
Ceramic Capacitors
Ceramic capacitors come in two classes:
- Class 1 (e.g. C0G/NP0): High stability, low capacitance. Ideal for precision applications.
- Class 2 (e.g. X5R, X7R): Higher capacitance but more temperature-sensitive. DPS exclusively uses X7R for better stability.
The biggest concern with ceramic capacitors is their failure mode: they tend to short-circuit rather than fail open.
Film Capacitors
Film capacitors use micrometre-thin metallised film as a dielectric. The capacitance per volume is low, but lifetime can be increased by a factor of 128 to 256 through voltage derating. Lifetimes exceeding 1,000,000 hours are achievable.
The traditional drawback: film capacitors require approximately ten times the volume of electrolytic capacitors. DPS uses state-of-the-art digital control methods to minimise the required capacitance, thereby drastically reducing the space requirement.
Conclusion
Ceramic and film capacitors are the most recommended types. Film capacitors are excellent for higher voltages, while ceramic capacitors excel in the low-voltage range. Electrolytic capacitors should be avoided in long-life applications.