Dear Saad Motahhir, frequency is one of the parameters in the design of an inductor. The inductor can be designed for a single frequency or a range of frequencies (due to harmonics). Therefore, your question should be made the other way around. For what frequency or frequencies your inductor is designed to operate? The magnetic field (W) store and current (i) in the coil are frequency dependent, the inductance is L = 2.W/(i^2). With W in Joules and i in Ampere for a given frequency. So for each frequency considered your inductor has a different inductance. A very simple Finite Element progam can show you that.
Dear José, thank you for your answer, i have another questions, first, what is the relationship between the inductor and the frequency ? Second, i have an inductor with 50Hz as frequency mentioned in its specification, so my question is can i use it build a DC-DC converter controlled by a command which has 1k HZ as frequency ?
Thank you,
Hi Saad. In principle, let's say "ideally," an inductor can "support" any frequency. Depending what the inductor is used for, of course, you will notice the effect of varying frequency, but the inductor, in the ideal, won't care.
For example, an inductor used in a transformer can in principle operate at any frequency, but the transformer will not support the same amount of power transfer as frequency changes. All else equal, the amount of current induced from the primary coil to the secondary coil will decrease, as frequency decreases, so a transformer designed for 400 Hz can be smaller than an equivalent transformer designed for 50 Hz operation.
The impedance of an inductor is Z = j(2 * pi * f)*L, where L is inductance. This says that the impedance rises as frequency rises, so that less current will flow through the inductor, all else equal, when frequency goes up. That's in part why transformers that operate at 50 or 60 Hz are so large and heavy, compared with those used at hundreds or thousands of Hz.
Then there are the practical realities. Inductors will usually also present some amount of capacitance. So inductors specified for low frequencies may possibly have higher stray capacitance than those specifically designed for high frequencies, resulting in the higher frequencies possibly shunting across the coils? A similar effect occurs in big electrolytic capacitors, where they begin to create resistive loads to very high frequencies, instead of behaving like capacitors.
To answer your question, can you measure the impedance of this coil, at 1 kHz? Try it and see how far it deviates from the theoretical. The stray capacitance might not be significant. Then the only negative aspect would be that the inductor, specified for 50 Hz, is much bulkier than it would need to be!
Thank you dear, but how we can design an inductor for a such frequency ?
Dear Saad,
Here you have a clue on how to design an inductor to any frequency:
http://ecee.colorado.edu/copec/book/slides/Ch14slides.pdf
For very high frequencies beware of stray losses.
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