how to calculate SRF of a inductor?
the self resonant frequency (SRF) of an inductor is computed by knowing the self capacitance (C), the inductance (L) and the formula f 1/(2 * pi * sqrt(L * C))
In electronics, capacitors and inductors have parasitic inductance and capacitance, respectively. For a capacitor, the inductance is primarily due to the physical dimensions including the leads. The lead inductance can be calculated using the equation Ldc 2L[ln(2L/r) - 0.75]nH where Ldc is the low-frequency or DC inductance in nano-henries, L is the wire length in cm, and r is the wire radius in cm.[1] Since a capacitor and inductor in series creates an oscillating circuit, all capacitors and inductors will oscillate when stimulated with a step impulse. The frequency of this oscillation is the self-resonant frequency (SRF). A capacitor or inductor behaves ideally only when its working frequency is well below the self-resonant frequency. As its working frequency increases, the effects of the parasitic inductance or capacitance became more pronounced until its self-resonant frequency, when the effective capacitance or inductance is zero since it is canceled by its counterpart. This number is commonly published for each capacitor or inductor by the manufacturer.
Inductor Design. (1) Single layer air cored. L N2?r? / 254(0.9+I) L inductance in uH. N number of turns. I coil length in mm. r coil radius in mm. (2) Multi-layer air cored, height equal to inner radius. H 0.34 √L/R. N 19.9 √L/H. L inductance in uH. N number of turns. H coil height in mm. d wire diam. in mm. R coils d.c. resistance in Ohms. (3) Multi-layer with height half the inner radius. H 0.323 √L/R. N 13.2√L/H. d 0.736H/√N. symbols the same as (2). (4) Coils wound on ferrite toroids or similar. N T√L/AL. L inductance of coil. A the inductance of T turns of the particular core. Coils wound on ferrites having an open loop, their design is based on the formula for air coiled coils, as shown in (1). The final inductance is usually found by trial and error but is typically 2 to 3 times the air cored inductance.
