That's a good question. It probably has to do with the manufacturing volume, the added cost, and the fact that one can get away with a more traditional solution that is good enough for many applications. There are other factors as well. One might ask why the Toshiba dual monolithic complementary JFETs are no longer in production. Sadly, times have changed. It is also true that class D amplifiers have improved and are displacing many class AB BJT designs. The biggest advantages of ThermalTraks are likely most valuable in high-end amplifier designs.
By the way, ThermalTraks got off to a tough start. First, many designers did not appreciate the best way to use them in their circuits, and the ON Semiconductor app note did not help. Secondly, there was a manufacturing problem that caused the forward voltage of the diode to jump significantly at times, probably due to some kind of thermal stress on the diode die. I saw it myself and it could cause an amplifier to be very suddenly very over-biased without warning. Charlie Hanson of Ayre and I discussed this many years ago. It drove him nuts.
Cheers,
Bob
I remember playing with the early Sanken devices that not only had the diodes but also an emitter resistor in the package, the SAP series. So you had a darlington with build-in Re and diodes, and you could build a very compact output stage with a pair of those.
Unfortunately, it was always the build-in Re that failed open at overload, making the device useless. The current STD devices chuck the Re.
Jan
Unfortunately, it was always the build-in Re that failed open at overload, making the device useless. The current STD devices chuck the Re.
Jan
You need to raise your standards!
My standards are pretty high. Criteria of optimization differ every time!
I wonder if one could make a scaled portion of the output stage with smaller devices and derive the bias level from that. I suppose that's what the OP is about too but on a much more extreme scale.
But then you have the issue of junction to ambient mismatch between the scaled devices and the main devices, so have then introduced a whole host of other problems.
But then you have the issue of junction to ambient mismatch between the scaled devices and the main devices, so have then introduced a whole host of other problems.
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