The $868.73 Op-Amp

Yes, you read that right; this here is an $868.73 operational amplifier, the Apex PA50A:

Apex PA50 Power Op-Amp

It doesn’t look like much, does it? Well at only ~1.5″ square, it’s not much larger than most power transistors. However, I can guarantee you it’s impressive. Most impressive. This is a power op-amp, which means it’s designed to deal with high currents and voltages. How high, you ask? Try 40 amps continuous (100A peak) at up to 130V. But you’re going to want a heat sink – this little guy may dissipate up to 400W internally.

JEDEC MO-127 HeatsinkNow sadly, these pictures aren’t mine, as I do not have a PA50 of my own. I also doubt I’d ever buy one (I just like to look at crazy-expensive parts on Digi-Key). However, this would be a fairly useful device. Normally op-amps are used at small-signal levels (from a few millivolts up to a few volts), and as such are only useful for amplifying sensors, performing filtering, etc. But with 40A and 130V to play with, you could drive multi-kilowatt speaker systems, go-kart motors, high-voltage transformers, etc (assuming stability with inductive loads). This baby would also make one serious output stage for a function generator, although its gain-bandwidth product is only 3Mhz. Interestingly, the datasheet lists “semiconductor testing” as the only potential application. Come on guys, I think a little more creativity is in order for such a product!

Now of course, you’re going to need one or two fairly beefy DC voltage sources to power the PA50, but I imagine they’ll cost you less than $800. And just what’s so special about this op-amp that drives up the cost so dramatically anyways? Frankly, I don’t know. Take a look at the following “equivalent schematic” provided in the PA50 datasheet:

PA50 Equivalent Schematic
Although this schematic doesn’t give values for individual components, we know that the final output MOSFETs (Q5,Q7,Q20,Q22) need to be rated for at least 100A (peak) and 130V. Well I’ve spec’d transistors like this in the past, and they’re not terribly expensive – perhaps $6-8 per device (double that if you want something really special). Even if all of the transistors in this package cost $10, that’s still just $220. Maybe there’s something costly about laying out all of this hardware in a single package? I’m certainly no expert in semiconductor design… Or perhaps the actual device is encased in 24k gold and diamond-studded? No, I guess they’re just trying to recoup development costs.

By the way, if you’re looking for high voltage instead of high current, try the Apex PA89, rated for ±600V output. It’s only $885.94 plus tax & shipping from Digi-Key. And don’t worry, I’m sure no one will question such a purchase. :)

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