CDRH104R Inductor Set and a Brief Trip Through History.

I needed some inductors for a project, and CDRH104R-type inductors seemed the best fit.
I only needed a few, so it would have been easier to buy them locally. But after browsing AliExpress, I decided to get a set of 10 values, five of each. Inductors are pretty useful things to have around for a radio hobbyist, and I figured it was a good call—they'd come in handy.
But that's just the preamble; the real story comes later.

These inductors cost quite a bit more here, and they're used fairly often. You don't always need just one value, which is why I ordered the set in the first place.
I once did a review featuring inductors, but those were bigger and more powerful.

It arrived in a small white envelope, with a sturdy zip-lock bag inside.


The inductors themselves were inside the bag.
10 values, five of each.
Values in microhenries: 10, 15, 22, 33, 47, 68, 100, 150, 220, 330.
I'll get to the measurements a little later; for now, here's a photo of how they arrived.
Everything comes on tape except for one value.


A piece of the tape. Everything looks neat so far; no complaints.


After that, I tested one inductor of each value. I'll hide the measurements behind a spoiler since there are a lot of photos.


The widest point is around the terminals.


Thickness: 3.78 mm.


The markings vary: some are bolder, others fainter, but overall they're fine.


The wire gauge varies with the inductor's inductance: the lower the inductance, the higher the current rating and the thicker the wire. Inductors with low inductance have a two-wire winding.


I won't claim these inductors are genuine, but their build quality, dimensions, and key parameters are all consistent with the .pdf]datasheet from Sumida.
Unfortunately, I can't check the DC resistance yet—I don't have the equipment—so, alas :(

Next, as I mentioned at the beginning of the review, a brief look back at the history.
Inductors have been made and used for a very long time. They come in all sorts of sizes, types, and values, and so on.
They're used as filter components to suppress interference, as ballasts in fluorescent (and other) lights, and as components that can store energy.
A typical home computer can easily have more than fifty of them.
There's the input inductor in the power filter, the passive power factor correction inductor, the group regulation inductor, and the output inductors. There are plenty on the motherboard too—in the CPU power supply, on the hard drive board, and on the graphics card. Even the sound card has some, though there they're usually used to suppress interference.

They were used in the past too, but became much more widespread with the advent of switching voltage converters.
They make it easy to build step-up, step-down, and buck-boost converters. And since these are switching converters, there's an inductor at the output as well. In short, you can't do without them these days.

But I'm getting carried away.
Time to move on to the practical part. But let me warn you right away: this review won't cover any cutting-edge converters running at several MHz.
It'll all be much simpler—and perhaps all the more interesting for it.

The old hands will surely recognize this circuit, but I'm almost certain many beginners won't.

A long time ago, back when I was still building caller ID units for people, there was the same need as today: getting 5 V to power electronics.
We mostly used KR142EN5A-series linear regulators—specifically, the KR142EN5A.
But everyone knows that despite its simplicity and low cost, it has one major drawback: low efficiency. This is especially noticeable when there's a large difference between the input and output voltages.
Then I happened upon this circuit design by chance. The internet didn't exist yet, and I no longer remember where I found it.

The trick is that a standard KREN regulator, a KT973 transistor, an inductor, and a few other small components form a switching step-down regulator.
No, PWM regulator ICs already existed, and there were even books about using them, but they were usually either very expensive or very hard to find.

The switching step-down converter circuit is very simple.
Its specs are, of course, pretty modest—not in the same league as modern PWM controllers with input ranges approaching 100 V or currents of 12–15 A.
The circuit works well over a 10–20 V range, with a load current of about 0.5 A (I didn't need any more than that), and a maximum of 1 A.


Using this schematic, I laid out a PCB, but with modern components.
I couldn't find a KT973 at home, so I replaced it with MJD117. It's also a Darlington transistor, with high gain but a higher voltage drop when switched on.


I made the PCB and picked out a handful of components, including an inductor from the ones described at the beginning of the review.


I soldered the board together.


The board turned out very compact; its length is about the same as the width of a matchbox.


The board worked as soon as I applied power, although the voltage was a little high.


I'll hide the board test under a spoiler since there are a lot of photos.

So, what can I say?
This circuit and board are shown mainly to demonstrate that even with a basic linear regulator (KR142EN), you can build a small converter whose efficiency is not much worse than that of modern converters (even inexpensive ones). I'm not considering circuits built around good ICs, with synchronous rectification and so on.
Obviously, these days even a dirt-cheap MC34063 circuit would be cheaper, smaller, more powerful, and better. But I wanted to show how things were before those came along. :)
This version doesn't serve any particular practical purpose—unless you happen to find yourself on a deserted island with only a linear regulator, a transistor, a few components, and a car battery, and want to charge your beloved smartphone so you can play your favorite birds. :)))

But just in case anyone wants to build my version of this converter, here's an archive with the schematic, PCB layout, and the inductor datasheet.

So, to sum up.
The inductors are perfectly decent, with good build quality.
They cost 2–3 times less than in our local brick-and-mortar stores.
The only downside is that you still have to pay for them, even if less.
The assortment includes a convenient range of values, covering most hobbyist applications.

I hope you found my review useful, or maybe just interesting. I did my best.