Self-Resonant Frequency: The Inductor Spec That Ends Your Bandwidth

Self-resonant frequency (SRF) is the point above which a chip inductor behaves like a
capacitor, and it is the real ceiling on where the part is still useful. Across the full 5,410-part
inductor extract from Walsin Technology (Walsin), the published SRF(min) figure ranges
from 0.015 to 20,000 — a number that cannot be read as one consistent scale, because 997 rows
(18.4%) publish exactly 0, and the series with the lowest real ceiling, WQQC, tops out at just
5.2 against a catalogue maximum of 20,000.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds Walsin’s full inductor
parametric export of 5,410 real parts (one QA test row, Test123999, is excluded from every
count here). Every part number below is real and checked against that extract.

What is self-resonant frequency and why does it cap usable bandwidth?

Above SRF, an inductor’s parasitic capacitance dominates and the part stops acting inductive.
A design that relies on inductive reactance above a part’s SRF is relying on a capacitor
instead, which is the wrong component for the job. As a working rule, keep your operating
frequency below roughly a third of the part’s SRF to stay clear of the resonance peak.

What is the real range of SRF(min) across Walsin’s inductor catalogue?

4,409 of 5,410 rows publish a nonzero SRF(min) value. Across those rows, the figure spans
0.015 (WLCW2520Z0J150PB, a 15,000 nH part) to 20,000 (several 0603(0201) parts in WLCM,
MCI and MCI-TM) — a published range of more than six orders of magnitude, which only makes
sense once you accept the column mixes scales rather than reading as one consistent number.

What does an SRF(min) of exactly 0 mean?

Not that the part resonates at zero frequency — it means the figure is not published. 997 of
the 5,410 real rows carry exactly 0 in SRF(min), concentrated in series built around
impedance rather than inductance: MCB/MHC Automotive Series (150 of 150 rows), CSME Series
(89 of 89), MCB-S Series (81 of 81), WLBD(HC) Series (71 of 71) and MHC-S Series (71 of 71) are
entirely zero. These are the same families whose Inductance column reports in ohms rather
than henries, which fits: a bead specified by impedance at 100 MHz does not have a
conventional inductor self-resonance figure to publish.

Which series has the lowest SRF ceiling in the catalogue?

WQQC Series, by a wide margin. Its 20 parts — a semi-custom family built in 14 irregular
rectangular sizes rather than standard imperial case codes — top out at 5.2, where the next
lowest ceiling in the catalogue, AIP Seires, reaches 48.0, more than 9x higher. Every other
series with a published SRF exceeds 40 at minimum.

Both are low-nH, low-RDC, high-current parts (2.9–4.4 A rated), built in flat, wide,
non-standard footprints rather than the usual square imperial cases. A flatter, wider winding
geometry plausibly increases parasitic capacitance and lowers SRF, which is consistent with
the pattern, but we have not confirmed the construction detail with Walsin.

Can I compare SRF(min) across two different series directly?

Only with caution, and sometimes not at all. The WLCW and WQCW wirewound families use the same
part-number scheme and the same case sizes, yet at 1608(0603) and 2012(0805) — and nowhere
else — their SRF(min) figures for otherwise identical parts differ by exactly 1,000x. See
WLCW vs WQCW wirewound inductor families
for the full measurement across 448 matched part-number pairs. The same two-scale pattern shows
up inside the WCI series individually — see
Walsin WCI multilayer inductors — where the
1005(0402) size reads 1.16–12.9 and every other WCI size reads in the hundreds to thousands.

Until Walsin confirms the unit in writing, treat any cross-series or cross-size SRF comparison
as directional only, not exact.

The short version

SRF(min) spans six orders of magnitude in Walsin’s export, but the column mixes a real
resonance figure with a “not published” zero and at least two different numeric scales. WQQC
has by far the lowest real ceiling in the catalogue at 5.2. Check the actual value against
your operating frequency, and do not compare SRF across series or sizes without confirming the
scale first.

Send us your operating frequency and inductance target and we will shortlist the real parts
that clear it, with the specific units question flagged where it applies.

Browse the full Walsin inductor range or ask us to cross a part.

Check it against the catalogue yourself. Cross-reference accepts one part number or a whole BOM column and prints the mismatches as plainly as the matches — qualification stays with you, which is the honest division of labour. Ready stock covers the inductor lines held in Hong Kong.

Frequently asked questions