I bought 100 units of the AO3401 and 50 units of the AO3400 from the same seller at the same time (minimum amount, sent in 10 unit strips).

I used the same soldering iron and was careful as when I was using the AO3401 for the other projects without problems. This was the first time using the AO3400.

My soldering iron is a 30W fine tip one, which connects to 220V directly, no transformer. I have been using it for over 15 years and, for example, I have repaired tablet screen ribbon cable tracks with hair-size transformer wire - the temperature is adequate for small stuff.

Only a few moments ago I learned this type of soldering iron may subjects the components to some stray voltages. I tested by holding an smd LED and touching the positive side with the soldering iron, causing it to very lightly turn on.

I guess I have been lucky so far that I havent destroyed more stuff..

 

I bought 100 units of the AO3401 and 50 units of the AO3400 from the same seller at the same time (minimum amount, sent in 10 unit strips).

Is this seller reputable and knowledgeable?

I bought my AO3400 and AO3401 on Ali Express; because I didn't feel like paying 30-40x more for something from a reputable seller. I don't know if I got rejects or counterfeits, but they work as switches and I haven't encountered anything didn't work. But I haven't checked to see if they'll handle 5A.

 

But I haven't checked to see if they'll handle 5A.

Similar situation. Bought 5 amp LM338 regulator chips from Amazon. They were wired in a constant current configuration but would only deliver 3 amps. Never again from Amazon.

 

I bought the mosfets from this shop: https://www.aliexpress.com/store/1911309

I have ordered from them in the past with problems...or maybe I havent put the parts to test properly.

 

I breadboarded the circuit using 100k and then 10k for the pull-down resistor. There was no measurable difference.

Still above the recommendation. When I get to a computer, I’ll calculate the desired resistance for the desired operation.

 

I bought the mosfets from this shop: https://www.aliexpress.com/store/1911309

I have ordered from them in the past with problems...or maybe I havent put the parts to test properly.

I consider any semiconductors purchased from Ali Express to be suspect. The sellers know little about anything they sell. I once considered buying a full reel of AO3400 because they're end-of-life. Then I remembered seeing reels of surface mount components being sold in an area of China where all they sell are counterfeits and it wasn't worth gambling $35 that they'd be something close. If I was a counterfeiter, I'd put dozens of good ones at the beginning of the reel.

You can't even be certain that the engineers employed by Chinese companies can even copy open-source designs like Arduino Uno. I have at least one where they substituted LM358 for LMV358. The former is definitely cheaper, but the latter has rail-to-rail outputs that the Uno counts on.

 

Still above the recommendation. When I get to a computer, I’ll calculate the desired resistance for the desired operation.

There is no recommended resistance. There is essentially zero current going into the gate. I usually use 10k for gate pull-up or down, but 1M will probably work.

 

A 1M pull-down resistor worked. I didn't measure turn off time for any of the resistors, but that wasn't what the OP was concerned about. A 100k pull-down would work in his test.

 

There is no recommended resistance. There is essentially zero current going into the gate. I usually use 10k for gate pull-up or down, but 1M will probably work.

Yes, I finally got it. Sorry for any confusion I caused.