Comment by ajross | Hacker News Reader

Comment by ajross | Hacker News Reader

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An even simpler reason is the way the device works. Like op-amps, a BJT transistor is very much a jellybean component. They all work the same. Sure, there are edge cases like high voltage/speed and very low/high power where you'd choose something different. But in general if you have a design with a BJT[1] used in a conventional way for sensor and control stuff you can drop in another part (or matched pair if you're doing something like an amplifier) of the same polarity without worry.

A current amplifier is a current amplifier, there's not a lot of complexity until you start worrying about stuff like base capacitance and whatnot.

So, sure, "at the right time" is correct, but really any good/cheap/available BJT that arrived at that time would have won.

[1] Op-amps are even more generically jellybean-like.

The "it works" part may be true for BJTs, but I think it's a stretch for op-amps. The number of Stackexchange and Reddit threads where people are struggling to debug the quirks of these ancient chips is pretty staggering.

I dunno. An op-amp is a high-impedance differential amplifier with (conceptually) infinite gain and monotonic behavior at the crossover. Hook it up in feedback to exploit those properties and walk away. Any other chip is going to work just fine as long as you aren't violating a voltage or output current spec or whatever.

It's true that it's possible to create a design that relies on a particular chip's behavior (like trying to drive an output directly and assuming it can do it vs. using, heh, a 2N2222 to drive the load). But those are pretty uniformly treated as "bad design". Op-amps "should be" jellybeans.

But these early chips are not that. The 324 has marked crossover distortion and problems with phase reversal, both have severe input and output voltage limitations, etc. Basically, they are a pain to use, especially in single-supply circuits, and there's little reason to keep using them.

They're insanely cheap. That's why they sell. They're cheap so the volume is there so they stay cheap.

I recall that I needed some 8-pin parts a while back to test something package-related. I looked around for the cheapest part I could find and guess what... it turned out that the 358 was the absolute lowest cost thing in the world in 8 pins. Cheaper even than dummy parts with no silicon in them.

That's how cheap they are.

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