Section 5 high speed pcb layout techniques texas instruments. Ohms law for inductance is the same as that used to combine resistances in series and parallel circuits. Therefore, it is important to design and analyze the stray inductance and capacitance of the direct current dcside circuit of an inverter. Inductance, capacitance, and resistance of a surrogate. Parasitic capacitance, inductance, and displacement. In order to minimize the need for an additional decoupling capacitor at high frequencies, this. It is important to estimate and minimize the stray inductance of the busbars in an early design stage. Stray inductance and capacitance in the circuits are critical parameters of the noise and surge voltage. As an example imagine the whole module as a plate capacitor with 2000. This method is based on the partial inductance theory. Pdf on nov 17, 2014, bozidar filipovicgrcic and others published estimation of load capacitance and stray inductance in lightning impulse voltage test. Show full abstract busbars are known to be a good solution for minimizing the stray inductance. Stray inductances cause various problems in a power inverter and should be appraised and minimized at an early design stage to avoid later required countermeasures and redesign after the device prototype has been built. This is because the coupling factor and the effects of parasitic capacitance and inductance between the conductors increase with frequency.
There are several capacitive elements in a transformer. Inductance, capacitance and resistance since inductive reactance varies with frequency and inductance the formula for this is x l 2. A simplified method of calculating busbar inductance and. Measure parasitic capacitance and inductance using tdr. They are both defined relative to the voltage produced.
Increase inverter reliability increase device capability, reduce inverter cost fy10 extract parasitics in conventional and proposed power module using electromagneticfield simulation tool model and simulate igbt switching behavior with. Stray capacitance on op amp inputs is a problem that circuit designers are always trying to get away from because it decreases stability and causes peaking. A stray inductance consists of the inductance of impulse generator and the inductance of connecting leads. It is much easier to measure the primary inductance and the. When these magnetic fields are created, they can produce an inductive effect. It changes the impedance of the coil and gives rise to parallel resonance. In evaluation of igbt, one phase circuit of inverter, as shown in fig. The digibridge was unable to provide a measurement for parallel inductance or series capacitance. Pdf stray inductance estimation with detailed model of. Oh, and always twist your wires send and return to minimize inductance. The oversize stray inductance distributing on the dcbusbar, which links dc capacitor bank to power devices, may. Parasitic capacitors are of minor importance at the given conditions. The net effect of the capacitance is normally seen by the lumped capacitance, cp, on the primary, as shown in figure 171.
Capacitors vary in shape and size, but the basic configuration is two conductors carrying equal but opposite charges figure. Lcr55a inductance, capacitance, and resistance meter. It is much easier to measure the primary inductance and the resonant frequency of the. Capacitors and inductors, pi hutchinson, 2004, mit.
Some coils are wound in multiple sections to reduce stray capacitance currentcarrying components have some stray inductance due to magnetic effects of current leads of resistors, capacitors, etc. The method is based on an analytical approach and the physical structure of inductors. The lcr55a has a residual capacitance of approximately 6pf in the 200nf range. The leakage current induced by stray capacitance in the. Stray capacitance an overview sciencedirect topics. The effects of the electric field can be represented with a lumped parasitic capacitance. A change in current in the conductor induces an opposing. In particular, the characteristics of a pair of busbars, and the use of the method are described. And9410 methods to characterize parasitic inductance and. Stray inductance is unintended and unwanted inductance in a circuit. Inductors, general technical information tdk electronics.
These results are in agreement with other publications. Resonance analysis focusing on stray inductance and. Partial stray inductance modeling and measuring of. An ideal inductor has an impedance that is propor tional to the frequencies. In many applications this is an undesirable effect and sets an upper. Stray capacitance is unintended and unwanted capacitance in a circuit. Application note an1001 a more realistic characterization of power. Johnson knows his stuff he is one of the world leaders in signal integrity and highspeed design. Chapter 30 inductors and self inductance inductance is to capacitance what current is to a stationary charge. Difference between inductance and capacitance compare.
Optimization of the stray inductance in threephase mosfet. Here, flowing charge flows in such a manner that it opposes the charge flowing behind it. The quantity l is called the inductance of the inductor, and we see that its units must be joules per ampere squared. The dc winding resistance is, rp, and rs is for the. A lowinductance, highfrequency film capacitor is used to replace the conventional electrolytic bulk capacitors to reduce size and enhance the. The equivalent lumped capacitance is represented by, cp and cs for the primary and secondary windings. Notice that the resonant frequency is shifted by 4. Using transformer parasitics for resonant converters a. Stray inductance in igbts dynamic testing platform has great influence on switching characteristics, such as switching speed, switching loss, voltage overshoot, and so on.
Returns mutual inductance, m, and mutual capacitance, c m. This document presents the measurement method of the stray inductance inclusive of the modules own internal inductance. Finally, an application to stray resonance analysis in the dc filter. Pdf a new method to extract stray inductance in igbts. In fact, any two surfaces at different electric potential, and that are close enough together to generate an electric field have capacitance, and thus act. Capacitance and inductance introduces two passive, energy storing devices. Pdf estimation of load capacitance and stray inductance in. Q charge and v voltage capacitance is the amount of charge stored per volt. Novel packaging to reduce stray inductance in power. This clumsy combination of units is more commonly abbreviated as the henry, 1 henry 1 ja2. Tdr can also be used to measure quantities such as the input capacitiance of a voltage probe, the inductance of a jumper wire, the endtoend. Pdf optimization of metallized film capacitor connection to reduce. Gate inductance higher than 20 nh could cause shoot through problem and harm system efficiency of synchronous buck converter.
The selfresonance and selfcapacitance of solenoid coils. Capacitance occurs winding to winding, turn to turn, windings to core and stray capacitances between terminals and case. Chapter 6 inductance, capacitance, and mutual inductance. Methods for reducing stray inductance of wires all about. In fact, any wires or component leads that have current flowing through them create magnetic fields. If fuse blows, replace with same see battery and fuse replacement. For an inductance measurement, the shorting blocks should not be used. Purpose of algorithm to calculate mutual inductance and capacitance of coupled lines basic description of algorithm the subroutine identifies the configurations and calculates the mutual inductance and capacitance between trace segments on a printed circuit board. Self capacitance of inductors antonio massarini and marian k. For modern vrm, the inductance in gate driving loop is typically around 10 nh to 20 nh, depending on pcb layout. Analysis and applications of parasitic capacitance.
The selfresonance and self capacitance of solenoid coils. This section looks at some key fundamentals of high speed pcb layout techniques so that hopefully the above scenario will never happen to you. The digibridge was used to determine the resistance of the film, along with its series stray inductance and parallel stray capacitance. Measuring parasitic capacitance and inductance using tdr. The website is full of information on designing for low inductance circuits. Stray capacitance the ultimate guide you need to know.
Parasitic capacitance can form between a metal table and a pcb sitting on top of it but less so with a table made from. Parasitic capacitance, inductance, and displacement current power. When two electrical conductors at different voltages are close together, the electric field between them causes electric charge to be stored on them. Why would anyone use tdr to measure an inductance or capacitance when there are many inductancecapacitance resistance lcr meters. This self capacitance is an important consideration at high frequencies. The inductor winding is partitioned into basic cellsmany of which are. The inherent inductance of the path length, of say and 0805 chip, is compensated out of the system. Capacitance measurement takes time and makes testing procedure more complex.
Inductance and capacitance are independent properties of two different electrical components. When using the 200nf range, note the residual capacitance and subtract this value from the measured value. Figure 2 shows the result of the stray inductance simulation of module 1 for the path dened by one half optimization of the stray inductance in threephase mosfet power modules aided by means of peec simulation. Parasitic capacitance, or stray capacitance is an unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other.
Kolar, senior member, ieee abstractparasitic capacitances of conventional transformers can be used as resonant elements in resonant dcdc converters in order to reduce the overall system size. Timedomain reflectometry tdr is commonly used as a convenient method of determining the characteristic impedance of a transmission line or quantifiying reflections caused by discontinuities along or at the termination of a transmission line. Parasitic capacitance, inductance, and displacement current. Its that phenomenon in which the current lags behind the applied voltage resulting in a phase difference.
In practice, the test object capacitance is often unknown. Chapter 17 winding capacitance and leakage inductance. It is important to remember that in a majority of higher frequency amplifiers, the stray capacitance may combine easily with some stray inductance, like component leads, in order to form various resonant circuits, which can also lead to a phenomenon called parasitic oscillations. Kazimierczuk, senior member, ieee abstract a new method for predicting the stray capacitance of inductors is presented. Parasitic inductance is an unwanted effect that is present in all electronic devices. Time domain capacitors and inductors are storage devices in the time domain capacitor that is c qv, where c capacitance. Load capacitance consists of voltage divider capacitance, test object and parasitic capacitances. While the inductance is a property of a current carrying conductor to build a magnetic field, capacitance is a measure of the ability of. The lumped capacitance is very difficult to calculate by itself. Here, c is the input capacitance of mosfet, which is characterized in a standard tester in lab. This rearrangement can reduce the stray inductance in the current commutation. C is called the capacitance of the device and has units of voltage charge one faradfis the capacitance of a device that can. Selfcapacitance of inductors power electronics, ieee.
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