Consequently the percentage of inductor peaktopeak current increases This

Consequently the percentage of inductor peaktopeak

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Consequently, the percentage of inductor peak−to−peak current increases. This discontinuous mode of operation is perfectly acceptable for this type of switching converter. Any buck regulator will be forced to enter discontinuous mode if the load current is light enough. HORIZONTAL TIME BASE: 5.0 ms/DIV Figure 23. Continuous Mode Switching Current Waveforms VERTRICAL RESOLUTION 1.0 A/DIV 2.0 A 0 A 2.0 A 0 A Inductor Current Waveform Power Switch Current Waveform Selecting the Right Inductor Style Some important considerations when selecting a core type are core material, cost, the output power of the power supply, the physical volume the inductor must fit within, and the amount of EMI (Electro−Magnetic Interference) shielding that the core must provide. The inductor selection guide covers different styles of inductors, such as pot core, E−core, toroid and bobbin core, as well as different core materials such as ferrites and powdered iron from different manufacturers. For high quality design regulators the toroid core seems to be the best choice. Since the magnetic flux is contained within the core, it generates less EMI, reducing noise problems in sensitive circuits. The least expensive is the bobbin core type, which consists of wire wound on a ferrite rod core. This type of inductor generates more EMI due to the fact that its core is open, and the magnetic flux is not contained within the core.
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LM2576 17 When multiple switching regulators are located on the same printed circuit board, open core magnetics can cause interference between two or more of the regulator circuits, especially at high currents due to mutual coupling. A toroid, pot core or E−core (closed magnetic structure) should be used in such applications. Do Not Operate an Inductor Beyond its Maximum Rated Current Exceeding an inductor’s maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate. Core saturation occurs when the flux density is too high and consequently the cross sectional area of the core can no longer support additional lines of magnetic flux. This causes the permeability of the core to drop, the inductance value decreases rapidly and the inductor begins to look mainly resistive. It has only the DC resistance of the winding. This can cause the switch current to rise very rapidly and force the LM2576 internal switch into cycle−by−cycle current limit, thus reducing the DC output load current. This can also result in overheating of the inductor and/or the LM2576. Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor. 0.4 A 0 A 0.4 A 0 A Inductor Current Waveform Power Switch Current Waveform Figure 24. Discontinuous Mode Switching Current Waveforms VERTICAL RESOLUTION 200 mA/DIV HORIZONTAL TIME BASE: 5.0 ms/DIV GENERAL RECOMMENDATIONS Output Voltage Ripple and Transients Source of the Output Ripple Since the LM2576 is a switch mode power supply regulator, its output voltage, if left unfiltered, will contain a
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  • Spring '19
  • Margaret Earle
  • Switched-mode power supply, Vout

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