Technical Bulletin – February 2019

Loading Constraints: Understanding Maximum Capacitance


The average PCB is home to an assortment of passive circuit elements, often including a broad array of capacitors of different types, ratings, and values. A capacitors sole function from a fundamental physical perspective is to store electric potential energy within an electric field between its electrodes. Circuit designers leverage the electrical properties of capacitors to perform a number of important tasks including filtering, signal coupling and decoupling, timing, transient suppression, phase shifting, energy storage, short term power bus hold-up, and more. The ability of capacitors to smooth fluctuations in the voltage across their terminals attributes to their use, often in abundance, directly across the main DC power input of an electronic circuit, providing downstream circuitry with a clean and predictable constant-voltage power source.

The power converter that feeds into the DC input of a given electronic circuit is subject to loading limitations based upon its design. Given that capacitors (void of parasitic resistance) are, by nature incapable of consuming any real power, one may be surprised to learn that there is indeed a maximum amount of capacitance that can be placed across the output of a AC/DC or DC/DC power converter. Read more (view pdf) >>

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