What?! There is a capacitor in my transformer?

Get a quick tutorial from James Tabbi, our Deputy Vice President of Exxelia's Magnetics Business Units, explaining what's interwinding capacitance

Exxelia recently designed an auxiliary transformer for a spacecraft application, where interwinding capacitance was of concern to the customer.  The controller chip they were using in their power supply was noted to be “rather sensitive to excess capacitance.”

Exxelia has also supplied thousands of driver transformers for use in a subsystem of the AN/TPQ-53 Radar System in which interwinding capacitance within the toroidal windings is held to a very demanding tolerance.

But what is interwinding capacitance? 

Capacitance in a transformer winding cannot be avoided. The voltage difference between turns, between winding layers and from windings to the core, creates “parasitic” capacitances in the transformer circuit.  These capacitances are shown as Cp, Cs, and Cw in this schematic diagram of an electronic transformer “equivalent circuit.”

Interwinding and distributed capacitance occur in transformers due to the physical separation of, and electrostatic coupling between, different turns of wire. In general, the capacitance presents itself between the different layers within a winding and between the outside layer of one winding and the inside layer of the next.  

In conventional magnetics, interwinding capacitance is a function of coil configuration – the geometry of adjacent conductors and separating dielectric media. Specifically, it is directly proportional to the shared surface area of the windings (shown in green and red below), the dielectric constant of the insulator between the windings (shown in gray below), and is inversely proportional to the separation distance through the dielectric media.


In high-frequency transformer design, leakage inductance and capacitance are often competing design requirements since the beneficial parameters that provide low leakage inductance also tend to increase the interwinding capacitance.

Excessive capacitance can cause undesirable common-mode noise transmission between transformer windings or between transformer windings and core or another ground connection.

Exxelia can assist with these design challenges when creating products that have to deal with interwinding capacitance, for all types of magnetic components.  

Important coil configuration design considerations must be made when capacitive coupling causes unacceptable signal transmission (for example, common-mode noise transmission or undesirable spurious ringing on a high voltage output).  Windings may be configured in a way that reduces the dV/dt voltages induced across dielectric media. Conductive screen(s) tied to preferred potential(s) can also be added between adjacent windings to reduce transmission.

If you’d like to learn more about interwinding capacitance or would like to discuss your specific magnetics needs, contact us sales.usa@exxelia.com 

Published on 04 Sep 2020 by Rebecca Charles

New Plug&Play filters for datacenters and mission critical facilities

Electronic equipment can leak sensitive information over conducted or radiated electromagnetic emanations, and signals transmitted down unprotected lines can potentially be intercepted. That’s why filters are implemented into systems to prevent EMI disturbances, as TEMPEST filters stop the high frequency EM signals (or noise) emanating inside the secured environment. Exxelia has a long history of manufacturing state-of-the-art electromagnetic interference (EMI) filtering technologies for space, avionic and defense markets. Thanks to this in-depth knowledge, Exxelia came to the conclusion that the installation of a product is as critical as its reliability, especially when shielding continuity and sensitive copper terminals are involved. That’s where Exxelia’s new full range of TEMPEST pluggable filters will save time and spare headaches! The 9260W series is a multi-socket line extension with a built-in 16A Tempest filter (minimum 60dB, from 100KHz to 1GHz), CE qualified according to EM 60950-1 standard. 9260W series Plug&Play solution is available with UK, US and EU standard plugs and can be provided with any other standard plug upon request. In addition, Exxelia completed its offer with the 9259W series of pluggable filters featuring various plug interfaces such as VGA/DVI, USB, Ethernet, Phone, Audio and much more. 9260W series and 9259W series are both fully compliant with EMC expectations and allow considerable time saving and cost-effectiveness. When a standard filter needs to be wired and shielded to each socket one-by-one before carefully re-closing the whole equipment, Exxelia new series can be installed using no special tools and with a smaller footprint. To all people handling sensitive information, a simple plugging operation is now enough to protect their data. Available now, 9259W and 9260W series are fully customizable upon request.

Innovative RF/Microwave components at IMS - Booth# 635 -

Ultra low ESR, high RF power and high self-resonant frequency The NHB series is a complete range of MLCC based on NPO dielectric material providing a very high Self Resonant Frequency and limiting the parasite Parallel Resonant Frequencies. The series is available in 1111 size with capacitance ranging from 0. 3pF to 100pF. NHB series offers excellent performance for RF power applications at high temperature up to 175°C and at 500 VDC. The lowest ESR is obtained by combining highly conductive metal electrodes and proprietary of new NPO low loss rugged dielectrics. NHB series particularly fits for high power and high frequency applications such as: cellular base station equipment, broadband wireless service, point to point / multipoint radios and broadcasting equipment. Typical circuit applications: impedance matching, bypass, feedback, tuning, coupling and DC blocking. 100% invar tuning screws with self-locking system Invar-36 is a unique Iron-Nickel alloy (64 % Fe / 36 % Ni) sought-after for its very low coefficient of thermal expansion. With 1.1 ppm. K–1 between 0°C and 100°C, Invar-36 is about 17 times more stable than Brass which is the most traditional and common alloy Tuning Elements are made of. The working temperature range in Space is so wide that this property becomes essential for a reliable and stable cavity filter tuning. Self-locking system is a technology commonly used on Tuning Element made of Brass or other soft “easy-to-machine” alloys but is innovative and pretty advanced when applied to hard and tough Invar 36. The design consists of two threaded segments separated by two parallel slots. After cutting both parallel slots, the rotor is compressed in its length in order to create a plastic deformation. Thus, an offset is induced between the two threaded segments which generates a constant tensile stress in the rotor from the moment threaded segments are screwed. High Q Factor Dielectric Resonators Dielectric resonators are designed to replace resonant cavities in microwave functions such as filters and oscillators. Exxelia has developed with support of ESA and CNES, a new high-end dielectric material, E7000 series, designed for high-end filters where high Q factor is requested. E7000 is Ba-Mg-Ta materials based that combines an ultra-high Q factor and the possibility to get all the temperature coefficients upon request. E7000 provides high-performance requested for space use in the frequency range 5 to 32 GHz, and guarantees up to Qxf > 250 000 at 10GHZ. Typical applications: Satellite multiplexing filter devices, radio links for communication systems (LMDS), military radars.

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