This white paper is a general discussion of distributed capacitance (Cd) in transformers with emphasis on measurement. We will discuss how capacitance occurs, references to a formula for calculating Cd, how capacitance is modeled, how Cd is measured (with three cautionary notes) and guidelines to aid in evaluating/measuring Cd.
Capacitance in a transformer winding cannot be avoided. The voltage difference between turns, winding layers, and between windings to core creates these parasitic elements. In general, part of the designers’ task is to keep capacitance to a minimum. On rare occasions winding capacitance is increased to reduce ringing in switching functions.
There are several capacitive elements in a transformer. Capacitance occurs winding to winding, turn to turn, windings to core and stray capacitances between terminals and case. To better understand the capacitance phenomenon, several references and discussions are provided. This discussion will be aimed at the measured capacitance that appears across a winding in a transformer.
Datatronic Distribution, Inc.
Datatronic Distribution, Inc. designs and manufactures a broad line of custom and standard wirewound magnetic devices for industrial, commercial, and high-reliability applications worldwide. The company’s magnetic components are found in power supplies, automotive electronics, computers and peripherals, industrial controls, instrumentation, medical devices and telecommunication equipment.
Magnetic components from Datatronic are qualified and/or certified to demanding performance, safety and quality standards: QS9000, ISO 9001/9002, UL, BABT, CSA, VDE and more. The company’s products include: switch mode power supply transformers and inductors, RF magnetics, common mode chokes, gate drive transformers, current sense transformers, pulse transformers, wideband RF transformers, telecommunications transformers and LAN filters.
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