[buescher]

Yeah. That and the LM393/LM339 type comparator-not exactly unknown though. But if I see those used appropriately in a circuit, it's the opposite effect of seeing 741 op-amps and 555 timers and TIP120 transistors.

Another one - the 33063/34063 type low-voltage DC/DC switchers. Like the TL431, hobbyists almost never use them but they're all over the place.

[SAI_Peregrinus]

I'm a big fan of the LT3574 switching regulator[1]. Makes it very easy to split an input supply out to dual rails for op-amps, or just for general regulation. It provides an isolated output without needing optoisolators or a sense winding on the transformer. And since they're flyback converters they can output a voltage above or below the input, allowing for wide variation in the input needed. And in typical LT fashion the datasheet is extremely thorough and well-written. Including a step-by-step design example. And plenty of reference designs. I use the +-12V output one quite a bit for powering op-amps, it lets me make use of the fixed 5V output third channel on my bench supply!

Not the cheapest though, about $7 each in qt1 on DigiKey, but that's rarely an issue at the hobby scale. And the ability to use a cheaper transformer and not need an optoisolator can make it save BOM cost even at large scale production.

[1] https://www.analog.com/media/en/technical-documentation/data...