At the time of writing, a conservative estimate showed upwards of 37,000 unique manufacturer part numbers for capacitors in stock at Digi-Key (114k including all packaging options). Simply maintaining that kind of SKU count involves an awful lot of paperwork, a lot of forklift mileage, and a lot of cash tied up in physical inventory. Being able to re-package those products to order and have orders on the loading dock ready for shipment in as little as 15 minutes after receiving an order? That’s a small miracle of modern industry.

Why spend so much effort on simple, two terminal components? The combinatorics of voltage and current ratings are definitely a factor, but the more subtle reason is that capacitors aren’t really that simple. The schematic symbols we use to represent them are lies by omission for convenience, and obscure details that are often a) rather important and b) not well treated in academia. For example, some capacitors have anger management issues and will try to set your house on fire or poison you if you provoke them. Others grow comfortable with the idea of being unemployed and if abruptly called upon to work again, will throw a hissy fit and quit in short order. Some capacitors are from Venus and exhibit wide parametric variations with environmental and application variables, while others are from Mars and are more or less oblivious.

Making informed design choices requires awareness and consideration of these varying qualities, and the objective of this work-in-progress is to offer the reader a guide to capacitor technology in an easy-to-swallow capsule with a (hopefully) non-drowsy formula.