Magnetics Business & Technology - Summer 2011 - (Page 23)

By Samir Kagalwala, Chief ConSultant • Power magnetiCS ConSultanCy GUEST COLUMN Cue-less About Q of an Inductor? The wire resistance changes when: its diameter reduced due to over stretching, its insulation scratched/cut through, there are excessive pin holes in its insulation, it gets nicks, knots and kinks in wire de-reeling and handling during winding, it is over heated during soldering, it is over pressed while applying insulating tape, it is over pressed during coil assembly, wire get scratched in core assembly, it gets overheated in varnishing/potting/encapsulating, it is mishandled in packaging and shipping. Would you not be frustrated to find a root cause of increased R among the umpteen possibilities? And after all the investigation, who wants to publicly admit his own fault? Given that manufacturing processes can induce higher resistances, which cannot be easily detected by other test procedures, Q remains the most effective guard against sending lower quality coils to customers. Not specifying and not checking Q considerably increases a risk of coil failure in the field. Should that happen within warrantee period, it can even bring financial disaster. We may not realize that when Q fails, specifying the Q is serving its purpose the most. And thereby, following the best practices in coil manufacturing helps a lot to meet the Q specs. That helps producing the coil right first time around. Q. The innocent looking single letter. What a meaningful single letter that is. Samir Kagalwala has more than 30 years experience in the industry. Presently, he is a chief consultant at San Diego based Power Magnetics Consultancy (PMC). Samir can be reached at samir@ where R is its internal electrical resistance and wL is inductive reactance coil.qxd:1/3 AD 8/3/10 2:54 PM Page 1 powermagneticsconsultancy.com. Square air at resonance. Given that an inductor with higher inductive reactance and/or lower resistance results into an inductor that has higher Q. With higher Q, the inductor approaches closer to its ideal state i.e. lose-less inductor. The inductive reactance and resistance are having same unit of measure i.e. Ohm. And, that makes the Q the unit-less measure of quality. That may be one possible reason why it is mysterious. We humans have difficulty grasping abstract things, don’t we? Simply put, the higher the Q, lower the losses and Our 29SA0806-XXX Family of SMD Air Coils are designed to higher the efficiency of the inductor in terms of deliverbe used in single and multiple LC filter applications. They ing the power. And, specifying Q means that the coil are great for communication devices such as Set Top Boxes, must deliver certain amount of power in relation to inFilters and Receivers. They have a frequency range of 5MHz put power. The specified Q number tells us maximum to 3GHz, inductance range of 6.0 nH to 27.0 nH; available amount of energy that can be lost in transformation of tolerances: 5% or 2%; SRF: greater than 2.0 GHz, operating power from input to output. Or in other words, it must temperature from -40°C to 125°C and Q greater than 50. deliver minimum certain amount of energy in relation to L: 2.75 mm max. W: 2.10 mm max. H: 1.5 mm max. input energy. With a ferromagnetic core used with the inductor, the inductance is improved considerably and thereby Q, for a same amount of copper. However, it also introduces additional resistive losses (R increases too). The inMeasuring success one micrometer at a time... crease comes from core losses, eddy current losses and hysteresis losses as the operating frequency increases. Straight forward enough? If so, why production personnel hate the Q, especially when all specs are met except the Q? 667 E Cochran St., Simi Valley, CA 93065 Well, that denominator of the Q (Resistance R) is the Contact: Jeannie Gu culprit. Not so much from the core resistance but from the 1-800-929-9888 wire resistance increase. Almost at every step of the coil Fax: 805-522-9989 manufacturing from material handling to shipping, there e-mail: frontiersales@frontierusa.com is a possibility of increasing the R if manufacturing prowww.frontierusa.com cesses are not diligently managed. Q. It’s one of the few single letters that when said stand alone, spurs many thoughts. It may take us back to an unpleasant memory of waiting in a long queue. It may prompt us to the Q that popularly stands for a ‘question’ in FAQ. Well, so far so good. Whatever Q stands for, it is simple, intuitive and easily understood. However, when it comes to a technical jargon, many in technical community may remain cue-less, or say Q-less, about the specified Q factor. The technical personnel, manufacturing and design alike, would think of it in terms of a quality of a product and, rightly so. However, they might not fully understand what that Q stands for or, what it really signifies, more so when it comes to an inductor coil. Given that, no wonder why coil manufacturing personnel get frustrated when an inductor passes all other specified test specs – inductance, hi-pot, number of turns - and NOT the Q. The function of an efficient inductor is to store the received energy and deliver it back when asked, ideally without losing any energy, regardless of the amount of current through the winding. However, the resistance of the copper wire causes power loss which in turn causes a loss of inductive quality. The power input minus the power loss (in terms of heat generated by wire resistance) is the power available at output to induce an inductance. By definition, the Q of an inductor is a measurement that represents the efficiency of an inductor as the ratio of its inductive reactance to its resistance at a given frequency i.e. Square air coil www.MagneticsMagazine.com Summer 2011 • Magnetics Business & Technology 23 http://www.frontierusa.com http://www.frontierusa.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2011

Magnetics Business & Technology - Summer 2011
Editor’s Choice
Designing Permanent Magnet Systems for Critical Applications
Growth in the Sensor Market Led by Magnetically Actuated Reed and Hall Sensors
Extending the Possibilities of Iron
Research & Development
Magnets • Materials • Measurement
Application • Component Developments
Guest Column: Cue-less About Q of an Inductor?
Industry News
Marketplace
Calendar of Events
Advertising Index
Spontaneous Thoughts: Sputnik Moments

Magnetics Business & Technology - Summer 2011