Inductor Isat vs Irms: 12 of Walsin’s 142 CSME and CSMEA Parts Publish Both at the Same Value, Counted for Romania

Inductor Isat vs Irms has no single ratio at Walsin. We divided saturation current by rated current on all 146 inductors that publish both: 130 are above 1, 12 are exactly 1.00 and 4 are below 1, down to 0.10. A Romanian designer cannot carry one rule of thumb across the three series.

Only 146 of Walsin’s 5,410 real inductors publish a saturation current at all, which we counted in a separate post. This post asks the next question for a power-supply designer in Romania: for those 146, how does Isat relate to Irms? Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the inductor parametric export published by Walsin Technology (Walsin), 5,411 rows of which Test123999 is a QA test row we exclude. We hold no Walsin inductor datasheet, so every number is the export’s. Every part number below is real.

What is the ratio of saturation current to rated current in Walsin’s data?

It runs from 0.10 to 2.33. We parsed Rated Current and Saturation Current on all 146 rows, converted milliamps to amps, and divided. Isat is above Irms on 130 parts (89.0 percent), equal to it on 12 (8.2 percent) and below it on 4 (2.7 percent). The median is 1.18, the minimum 0.10 and the maximum 2.33. In the 4 below 1, the part saturates before it reaches its thermal rating.

We have not seen this ratio counted per series anywhere. The 146 parts split 89 CSME, 53 CSMEA and 4 MIP-H, and none of the three behaves like another.

Which Walsin series publish a saturation current, and what does each one show?

Three, and they disagree on the sign of the margin. We computed the ratio per series. CSME runs from 1.000 to 2.333 with a median of 1.176, CSMEA from 1.065 to 2.178 with a median of 1.217, and MIP-H from 0.100 to 0.611 with a median of 0.367.

The MIP-H case is the sharpest. MIP1608H4R7MBP publishes 600 mA rated and 60 mA saturation, a ratio of 0.10; MIP1608H2R2MBP publishes 600 mA and 230 mA, 0.38; MIP2012H4R7MBE publishes 800 mA and 280 mA, 0.35; MIP2012H2R2MBE publishes 900 mA and 550 mA, 0.61. For the thermal and magnetic definitions behind this, see rated current vs saturation current in chip inductors.

Why do 12 CSME parts publish identical Isat and Irms?

Because six inductance values in one size publish the same number twice. We listed every row with a ratio of exactly 1. All 12 are CSME0645D, size 6060, at 15, 33, 47, 68, 82 and 100 uH, each present as an M part and an N part, and every one reads Isat equal to Irms.

A thermal limit and a magnetic limit landing on the same value to one decimal place, six times across a 15-to-100 uH ladder, is more likely a convention than a measurement. The export does not say which. The file has 14 columns and none states the inductance drop or temperature rise used to define either figure.

Does the margin between Isat and Irms change with inductance or size?

Yes, and it shrinks as inductance grows. We grouped the 142 CSME and CSMEA parts by inductance. Median Isat over Irms is 1.55 up to 1 uH, 1.36 from above 1 to 4.7 uH, 1.10 from above 4.7 to 10 uH, 1.11 from above 10 to 33 uH and 1.11 above 33 uH. By case size the medians are 1.37 at 4040, 1.11 at 5050 and 1.16 at 6060.

46 of the 142 parts (32.4 percent) sit under 1.10, and 12 sit under 1.05. A designer who sized to Irms and assumed Isat would be 20 percent higher would be right on 76 of the 142 and wrong on 66. We counted it that way so the reader can repeat it.

How many of the 146 are really 80?

Fewer than they look. CSME and CSMEA publish the same part under two series names, and the tolerance letters double most rows. We took the 142 rows and removed the tolerance and series name, keeping case size, inductance, rated current, saturation current and DCR. They collapse to 80 distinct data lines. CSME0418D-2R2M and CSMEA0418D-2R2M both read 2.2 A and 3 A. So the honest sample for a CSME Isat rule is 80 data lines, plus 4 from MIP-H.

That also means the 12 equal rows are 6 distinct data lines, not 12. The wider pattern of repeated data is in chip inductor second source.

What should a Romanian designer take from a ratio that no column explains?

Treat Isat and Irms as two numbers to check, not one number with a margin. The file gives Isat on 146 parts, no test condition on any of them, and a ratio that runs from 0.10 to 2.33.

1. Read both limits against your own waveform. Compare Irms with your RMS current and Isat with your peak, as covered in the post linked above.
2. Where Isat equals Irms, assume no headroom. That is 12 parts, 6 distinct data lines.
3. Where Isat is below Irms, size to Isat. That is 4 MIP-H parts.
4. For the other 5,264 inductors, the export publishes no Isat at all. Request the Walsin datasheet for your exact part number; we hold none for inductors.

Our free cross-reference tool shows the published values beside the original and states differences instead of ticking a box. What is in Hong Kong is on ready stock: 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed. The range sits on the inductor page.

The short version

We divided Isat by Irms on all 146 Walsin inductors that publish both. 130 are above 1, 12 are exactly 1.00 and 4 are below, with a median of 1.18 and a range of 0.10 to 2.33. CSME and CSMEA keep Isat at or above Irms; MIP-H keeps it below on all four parts, down to MIP1608H4R7MBP at 60 mA against 600 mA. The margin narrows with inductance, to a median of 1.10 to 1.11 above 4.7 uH. The 142 CSME and CSMEA rows collapse to 80 distinct data lines. We will not tell you a part has headroom. We will show you the two cells. Confirm against both datasheets and qualify in your own circuit.

Send us the inductor off your BOM with your peak and RMS currents, and we will show every Walsin candidate’s Isat and Irms side by side, blanks included. And a question back: when your inductor datasheet gives one current figure, which of the two limits is it?

Frequently asked questions