Choosing an Inductor for a Buck Converter

Size a buck converter inductor on saturation current, not rated current, and expect to
ask Walsin Technology (Walsin) for it directly. Only 146 of the 5,410 real parts in
Walsin’s inductor export publish a saturation current figure at all, and they sit in just 3
of the 47 series — CSME, CSMEA and MIP-H. The other 5,264 parts give rated current alone,
which tells you the thermal limit, not the point where the core stops working.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the full Walsin
inductor parametric export used in this post — 5,410 real rows once the one known QA test
row is excluded. Venatech holds no Walsin inductor datasheet PDF, and 208 parts across the
VEFL, WIP, SCM, SCA and BIH series have no datasheet at all. Confirm every specification below
against Walsin’s own documentation before design-in. Every part number is real.

Why is rated current the wrong number for a buck converter inductor?

Rated current is usually a thermal limit — the current at which self-heating raises the
part’s temperature by a fixed amount, typically 20°C or 40°C above ambient. Saturation
current is a magnetic limit — the current at which the core stops storing energy linearly
and inductance collapses. In a buck converter, exceeding saturation current during a load
transient drops the inductance exactly when the control loop needs it, which can spike
peak current far faster than the thermal rating would suggest. Designing to rated current
alone assumes the two limits line up. The data shows they frequently do not.

How many Walsin inductors actually publish saturation current?

146 of 5,410, or 2.7%. Venatech has published this figure before: it is the headline fact
behind Rated current vs saturation current in chip
inductors. The other 5,264
rows give rated current only, and for a buck converter design that is the wrong number to
rely on without separate confirmation.

Which Walsin series publish saturation current, and which do not?

Exactly three, and the split is all-or-nothing by series — no series publishes it on some
parts and not others.

That means WLCW (791 parts), WCI (720 parts) and WQCW (569 parts) — the three largest
series in the whole export — publish no saturation current at all, alongside every other
series including the automotive-marked ones. If your buck converter candidate is outside
CSME, CSMEA or MIP-H, the figure simply is not in Walsin’s parametric data and has to come
from elsewhere.

Can saturation current be lower than rated current?

Yes, and when it happens it is the exact trap a buck converter designer needs to avoid. All
4 MIP-H Series parts publish both figures, and the gap is large:

MIP1608H4R7MBP is the extreme case: rated 600 mA, saturated at 60 mA, a tenfold gap. A
design that sized this part on rated current alone would be running the core deep into
saturation at one tenth of the number printed in the rated-current column. By contrast, the
CSME and CSMEA series generally publish saturation current above rated current — their
1.0 µH parts are rated 3.2 A and saturate at 4 A, and their 2.2 µH parts are rated 2.2 A
and saturate at 3 A — which is the more common pattern for a dedicated power inductor but
is not something you can assume without the figure in hand.

What should I do if my series does not publish saturation current?

Three options, in order of reliability. First, ask Walsin for the saturation current of the
specific part number — it may exist outside the parametric export we hold. Second, if no
figure is available, treat the published rated current as an upper bound you have not
verified against core saturation, and build in margin rather than designing to the limit.
Third, consider a CSME, CSMEA or MIP-H part if the application allows it, since those are
the only series where both figures are confirmed in writing by Walsin’s own export. None of
these substitute for a datasheet, which Venatech does not hold for any Walsin inductor
line; always confirm before committing a design.

For the construction differences behind current rating across Walsin’s inductor families,
see Multilayer vs wirewound chip
inductors. The full range, including CSME,
CSMEA and MIP-H, is on the Walsin inductor page.

The short version

Saturation current, not rated current, is the number a buck converter design should be
sized against. Walsin’s own export publishes it on only 146 of 5,410 parts, concentrated
entirely in CSME, CSMEA and MIP-H. Where it is published, it can sit well below rated
current — by a factor of ten on MIP1608H4R7MBP — which is exactly the failure mode
relying on rated current alone would miss.

Send us your target inductance, current and footprint and we will tell you which Walsin
series actually publishes a saturation current figure for it, or confirm that none does.

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