How to estimate switching power supply power consumption in the inductor (1)

In switched power consumption power in many sources, including the MOSFET, input and output capacitance, controller's static electricity consumption and inductance, this article focuses on the by the inductor, inductor losses on power consumption, essentially in two parts, namely the core (core) own power consumption and Inductively wound caused by power consumption.

Inductor based on the principle of

Power Inductors through Exchange week period breakover time, the energy stored in the magnetic field, and disconnected, the energy of the storage available to load, the inductor is wound in a Ferrite cores, and the air gap of winding.

To learn more about inductors as power consumption, it must be on the basic composition of inductors, including magnetomotive force, field strength, magnetic flux density and magnetic field and magnetic susceptibility and resistance, etc.

In order to avoid an overly complex involved in the actual principle of electromagnetic fields, thereby simplifying the magnetic components.

In switching power supplies, inductor of magnetic fields are included in the core, magnetic field, mainly by the current flowing through the coil cores of the winding, with Weber (Weber) as the unit of magnetic flux density, magnetic field is multiplied by the core cross section area, magnetic density to Tesla (Tesla), equivalent to the magnetic field strength multiplied by the cores permeability.

By Henery ' s/m-permeability rate of a specific substance material itself allows flux through ability, material permeability rate higher, magnetic flux through the easier.

Power Inductors contains a combination of ferrite and air, so will its valid values are approximately between magnetic substance and air permeability.

In this case, about magnetomotive force multiplied by the intensity of the magnetic core of the effective length, the effective length is the magnetic flux around the core of the path length (figure a) and (B) of the magnetic circuit, F (t) can be seen as a source of magnetic flux, finally, reluctance is a substance on the magnetic field of the fight, but also is magnetomotive force relative to the flux ratio is also the core entity structure in the formula.

　　

　　

　　

(Figure a) magnetic circuit diagram

　　

Inductance in the operation of the two laws, namely the ampere's law (Ampere ' s Law) and the Faraday's law (Faraday ' s law), ampere's law and flows through the inductor cores magnetic field of the current size of the inductor cores, magnetic field strength in the entire core length can be considered consistent.

Faraday's law is inductors on voltage relative to the core of magnetic flux through equations. (Figure a) (A) shows the power inductors feature block diagram, figure a (B) for a power inductor equivalent magnetic circuit, to join the air gaps will be low reluctance ferrite material tandem a high magnetic components, causing most magnetomotive force appears in the air gap.

Inductor value can be calculated, as a result of ferrite materials with high permeability and therefore quite easy to make magnetic flux through, this will help maintain the magnetic flux in the inductor cores, while creating a smaller size and high likelihood of magnetic inductors.

This may also be made by the above analysis out of the equation, inductance CDMA related core material, you can use smaller cross-sectional area.

　　

Inductor works

Power inductor works as follows.

Whether it's bootstrap or buck converter, when one side of the switch in power supply voltage to the inductor, will result in increased, according to current law, current in amperes changes will cause the change of the magnetic field magnetic material, then thrown through the inductor cores for magnetic flux density and magnetic field increases to rewrite the equation. On the other hand, in a time-switch broken off time, remove the power supply voltage, the magnetic field will begin to decline in size, resulting in lower inductance magnetic core, according to the first law of motion, reducing the pull rate will bring inductor voltage changes.

(2) to thick line shows a sine-wave method change input voltage function diagram, called a tardy turning road, and to occur incrementally to measure the relative response of nonlinear, and while there is a delay interval, thus turning called hysteresis, hysteresis interval is the inductance magnetic core power consumption of core material characteristics.

　　

　　

　　

(2) sketch of hysteresis turning road

　　

Inductor cores for power consumption

In the Exchange week period, because of the magnetic core magnetic energy changes caused by energy consumption for breakover time to be deposited on cores, magnetic energy and shuts down the extracted from the core differences between magnetic energy.

Therefore, into the core of the total energy to figure II B-H turning road, shaded area to the size of the volume on magnetic core. When the inductor current decline, magnetic field strength decreases, magnetic flux density is a figure of a different path in the second (according to the direction of the arrow) changes, the majority of energy will enter load, storage of energy and the difference between the issue of energy is the energy consumption. Core energy consumption for the turning road B-H drawn area by the volume on magnetic core, this energy by switching frequency is power consumption. Hysteresis losses according to function, the majority of ferrite, n approximately in the range of 2.5 to 3, but this only in the core has not become saturated State, while the exchange rate fall within the scope of the operation. Figure 2 in the shaded area shows the turning road, B-H first quadrant is the magnetic flux density of operation area, because most of the bootstrap and buck converter are as inductance-current operation.

Inductor cores of a second source for Eddy current losses.

Eddy current is the core material for magnetic flux variations caused by the current law, based on a double time (Lenz ' s Law), magnetic flux change will bring a creation and initial flux change in the opposite direction; this is called reverse current eddy currents, will flow into theConductive core materials, and power consumption. This can also be seen by the Faraday's law. By eddy currents caused by the core power consumption, proportional to the magnetic flux variation squared. Because of the magnetic flux rate directly proportional to the voltage, power consumption of the Vortex current increases with the square of the inductive voltage increases, and directly with its wave width. Interval relative to the hysteresis, the cores of Eddy current losses are usually due to core material of high resistance and low, usually on many core depletion, also included in the range and the hysteresis of the magnetic core Eddy current losses.

To measure core consumes typically quite difficult, because it contains a rather complex used to measure magnetic flux density in test settings, as well as on the estimation of the hysteresis turning road.

So far many inductor manufacturer did not provide this information, but some can be used to compute inductor cores of depletion of a number of characteristic curve, which can consist of ferrite materials manufacturer, peak to peak magnetic flux density and frequency functions. If you know the inductor cores the CDMA specific ferrite materials as well as the volume size, you can use the curve to effectively estimate core losses.

This type of curve, for example (Figure 3) ferrite materials, is to join the bipolar magnetic flux change signal sine wave voltage changes, when made way to square-wave pattern (contains more high frequency harmonics) and single-pole magnetic flux change, functioning DC to DC converter core depletion estimates, you can use the base frequency and 1/2 of the peak to peak magnetic flux density, inductor of volume or weight can also be calculated by measuring the or.

　　

　　

　　

(Figure III) cores depletion information map (1)

　　

Part of the inductor manufacturer has provided core depletion, or can be used to obtain a more accurate estimation of magnetic power losses in the part of the equation, manufacturers inductors information specifications, provide inductor cores consumption equation.

Magnetic core depletion is CDMA dual-mode constants (K-factors) formula, therefore you can by frequency and peaks on the peaks of inductance-current ripple function to calculate the magnetic core losses. On the other hand, manufacturers will graphically, provides many inductors product core losses.

　　

　　

　　

(Figure 4) core depletion information map (2)

　　

Inductor winding power consumption

In addition to the inductor cores for power consumption, consumption will occur in the inductor winding parts.

In DC, winding power consumption comes from the DC resistance as well as through the inductor RMS currents. Entities on a small inductor typically use smaller winding, therefore also for smaller cross-section area, resulting in a higher DC resistance. In addition, numerical large inductor will have more number of winding coil, so it will be winding length increases, the relatively high electrical resistance.

In DC, winding of DC resistance will result in the winding depletion, when the frequency increases, called surface effect (skin effect), will result in the winding resistance increases.

Surface effects occur in the inductor on current I (t) change, this current change would create orthogonal to the current flux variations; in accordance with the law, a double-flux change, will have the original flux change reverse current flux of Eddy current, so the current direction is opposite the original current. The induced magnetic flux in the conductor's central highest, while the lowest in the surface of the conductor, which will result in the center of the current density, will increase the frequency of the DC values from the original. This effect is derived by: current be pushed to the surface of the conductor, leading conductors Center lower overall current density, surface current density and higher. 由于铜的电阻率相同、且� [1] [2]