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first of all, I searched enough, but did not get the simple answer... What's the different between color ring & power Inductor... enter image description here

Is it all about wattage?

Color rings are mainly 0.25W, Don't know the other one's watt...

I'm trying to remake a "DC boost" circuit with MT3608(B6289)... Can I use a color ring Inductor Instead of this...?

enter image description here

Schematic: enter image description here

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    \$\begingroup\$ It is not all about wattage. There are things like core frequency response (resonant frequency and parasitic capacitance), noise, shielding, losses, and core material (which can limit the type of construction). The "ring" inductor is called an axial inductor. You can use it, if it fits the bill but as you noticed its lower power but if can support your current then sure. \$\endgroup\$
    – DKNguyen
    Commented Jan 27, 2020 at 5:19
  • \$\begingroup\$ Thanks... Anyway, I'm trying to use it on a low power unit, I think It should work, worth a try... \$\endgroup\$
    – BLUE
    Commented Jan 27, 2020 at 5:27
  • \$\begingroup\$ Tiny axial inductors tend to have a high DC resistance, which translates to a low Q value, its efficiency as an inductor. The small bobbin or pot-core type often use the heaviest gauge of wire possible, thus have a much higher Q. \$\endgroup\$
    – user105652
    Commented Jan 27, 2020 at 6:01

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The most important property of an inductor used in an inverter circuit is the current allowed to run through it. A tiny axial inductor may have the same inductance as a radial one but most likely it has a much smaller maximum current.

The inductance needed depends on the voltage spread you want to achieve.

I recommend to stick to the datasheet of the regulator chip closely. They usually give figures which inductors you should use for which voltage and current.

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  • \$\begingroup\$ Thanks, I re-check the datasheet, and yes, there is "Inductor Selection" written... \$\endgroup\$
    – BLUE
    Commented Jan 27, 2020 at 6:42
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Inductors have several important specifications. It does not matter what the construction is, axial lead, pot, whatever, as long as it meets your specifications. Generally the larger and more expensive component will tend to have better specifications. Once you've met your converter specifications, for power throughput or efficiency, there's no need to go better.

Read the specifications for the component you're going to buy. If they aren't supplied, don't buy the component, unless you're prepared for measurement or trouble.

Once you've met the headline inductance specification, the next two are DC resistance and maximum current before saturation Imax. DCR is easy to measure yourself, Imax is rather trickier.

In a boost converter, the Imax is perhaps the most important, The inductor has to be able to draw the peak input current (not the smaller mean or output current), without losing inductance to saturation. If the inductor saturates, the current drawn will rise precipitately, probably blowing up your driver IC switch, and increasing I2R losses dramatically even if the switch survives. A higher Imax allows you to store more energy per cycle in the inductor, so increase power throughput.

DC resistance is important for losses, and for heating of the component due to the current flowing. Lower resistance is better.

Another parameter that will be relevant is Self Resonant Frequency or SRF. This is due to the capacitance between the windings forming an LC resonator with the inductance. For standard power converter circuits, you'd use the component at a switching frequency well below the SRF.

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  • \$\begingroup\$ To some degree the construction does matter, as it may force the use of small gauge wire, hurting the Q value and its saturation value. Except for RFC chokes for RF signals, I normally stay away from small axial inductors. I would never use one in a SMPS. \$\endgroup\$
    – user105652
    Commented Jan 27, 2020 at 6:06
  • \$\begingroup\$ @Sparky256 you see the 2nd half of that sentence - go by the specifications. An axial leaded one may use thinner wire, it may not. While different constructions generally have different target applications, if your applcation can be met by a particular specification, go with it. A decade ago, I found the little 3.2x2.5mm blue SMD inductors were right for a set of very small DC-DC converters I needed to iimplement, they are built pretty much like the axial ones, but without leads. \$\endgroup\$
    – Neil_UK
    Commented Jan 27, 2020 at 7:31

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