FDA59N30 Transistors, Attempt No. 2

I recently reviewed some FDA59N30 transistors I bought on AliExpress. I mentioned then that I’d ordered a couple dozen more, and here they are.

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To be fair, delivery was relatively quick: I ordered on May 8 and received the package on June 2. I have no complaints about the packaging either; I wish everyone shipped things this way.

But there’s a catch. Some time later, the seller sent me this notice:

and gave me a link to their other store. The product link now leads to the transistors in that store, since the old listing is no longer available.
It’s a bit strange: the first store had a wide selection and lots of good reviews. Maybe they decided to change things, but I think the second store could be useful too. The prices seem to be the same, which is another indication that it’s essentially the same store.



But as I mentioned, I ordered a couple of other types of transistors too. Everything was packed in little bags and labeled.
I also ordered:
1. HY3708. They’re a good fit for the low-voltage side of inverters. I have a couple of transistors from a factory-made inverter, so I’ll have something to compare them with.
2. 20N60C3. These are high-voltage transistors used in power supplies. For some reason, they cost a fortune here.




I’ll talk about those two types another time. Today, a quick look at the FDA59N30. As you may remember, these are power transistors rated for continuous DC operation. By the way, I finished routing a new four-channel power module quite a while ago; maybe I’ll build something with it soon.


They look just as inconsistent as before—actually, no. Last time I got some with matching codes; this time there was only one or two such pairs. Everything points to these being genuinely used parts, not remarked fakes.


Even the markings vary. For example, the second transistor in the top row has a completely different style.
Almost all are from Fairchild, but there were also three from Onsemi.


The two key parameters usually checked are gate capacitance and on-resistance. Ideally, you’d also check the transconductance and breakdown voltage, but that’s difficult, inconvenient, and time-consuming.


I numbered all the transistors and started testing them.
1, 2. Gate capacitance. A reminder: to measure it correctly, you need to apply voltage to the transistor—in this case, 25 V. The photo shows measurements of the same transistor with no voltage and with 25 V applied. The correct reading is on the right; the one on the left isn’t.
3, 4. On-resistance should also be checked under load. For these transistors, that means 29.5 A with 10 V on the gate. But since milliohm-meter readings correlate directly with measurements under load, and I only needed to assess the spread, I used the simple method without current. The photo shows the samples with the lowest and highest resistance.


For convenience, I put the results in a table. The transistor with the unusual marking is highlighted in green, and the ONsemi transistors are highlighted in blue.
As you can see, most have an on-resistance of around 42–44 mΩ, but some are at 40 mΩ. It’s also worth noting that all the ONsemi transistors are around 40 mΩ as well.
If you remember my previous review, the original parts bought locally, a few Fairchild transistors from the same batch, and all the ONsemi ones were around 40 mΩ. So the results are the same, which is an indirect sign that these are genuine parts.



So, what can I conclude? It’s basically the same as last time: they’re just transistors. I’ll use them in electronic loads, since I haven’t seen any particular problems so far. I might set aside the ones with higher resistance for experiments.

That’s all for now. I’d be glad to hear your thoughts and guesses. Thanks for reading :)