Used HY3708 transistors

Along with the FDA59N30 transistors I recently showed, I ordered a couple of other types. Today I'm reviewing one of them: the relatively low-voltage FDA59N30.

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This won't be a very long review, but I'll try to make it as informative as possible.
I ordered three types, one of them for the low-voltage side of an inverter, and partly just out of curiosity.


The manufacturer is Huayi. Damn, even the name sounds a bit indecent—definitely Chinese. But lately I've been coming across transistors from this company more and more often: datasheet


Transistors from this company were actually used in one of the inverters I modified. When I wrote the review of the previous transistors, for some reason I thought I'd ordered the same ones, but I got them mixed up. The inverter had HY3906, which can handle more current and have lower resistance, but are rated for 60 V rather than 80 V. I specifically wanted the 80 V ones.


The key specs are 80 V and up to 170 A.


They're standard switching transistors, but when I read further through the datasheet, I was a little surprised to find that they can also operate in DC mode.


They clearly look used. No surprises there, though I wish the leads were a bit longer.


The first key parameter is gate capacitance.


I put together a simple “test rig,” though afterward I realized I could have soldered on a socket so I wouldn't have to clip on the alligator clips every time.


A reminder: gate capacitance is measured with the transistor under voltage. For the HY3708, that's 25 V. Gate capacitance depends on this voltage and on what else is connected.
The photo shows three measurements:
1. No voltage applied; only the RLC meter is connected.
2. No voltage applied; the power supply is connected, but its output is off.
3. With voltage applied—the correct result.

According to the datasheet, it should be around 6100 pF. In reality, it was closer to 5900–6100 pF.


I also measured the on-resistance, this time using a YR1030 milliohm meter, and put all the results in a table.
1. The top section shows the capacitance and resistance measurements for all 20 units.
2. The bottom section shows the on-resistance versus gate voltage for five samples.


Of course, the proper way to measure resistance is as specified in the datasheet: by measuring the voltage drop at a specified current and gate voltage. For these transistors, that's 85 A and 10 V. But I don't have an easy way to get 85 A, so I tested them at 20 A instead. It's also easier to calculate that way.


I made a few changes to the test rig and screwed the transistors under test onto a heatsink.


The test included transistors numbered 1, 5, 10, and 20. Their channel resistance came out to around 34–35 mΩ, which is very close to the values measured with the milliohm meter.


Naturally, you might wonder why I tested transistors 1, 5, 10, and 20, but not 15. It's simple: some of the transistors have solder on the flange, which prevents them from sitting properly on the heatsink.


Apparently, these are “quirks” of the desoldering process. One transistor even had a resistor stuck to the back, soldered onto the flange—a bonus :)


Conclusion.
In my opinion, these look like genuine transistors—or, more precisely, genuine Chinese transistors. Interestingly, in my experience, Chinese components are much less likely to be counterfeited.
So if you need this type, I recommend them. They're good.

That's all for now. I hope you found this useful.