On Semi introduced in 2006 a series of complementary power transistors, called ThermalTrak. These come in five-lead TO-264 packages and use the extra two pins for an integrated, isolated temperature-sensing diode. The transistors are reasonable parts, with 230 to 350V ratings, and with 30MHz fT. There are four sets of parts in the series, with pretty detailed datasheets, except, hah, little information about the diode. For example, what's the current ratio for the same "Vbe" drop?
There was an ON Semi press release in Jan 2006, and an EETimes article in Oct
2005.Most class-AB amplifier biasing circuits use a temperature-sensing transistor, so an adjustable Vbe ratio may be created for settable biasing.
In this note they use six output transistors (three each in parallel for push and pull), giving them six sensing diodes to wire in series. They substitute this set of diodes in place of the usual trimmed multiplied Vbe, to develop about 3.4 volts to drive two emitter-follower stages plus the output transistors. They have no provision at all for bias adjustment.
The driving transistors include one each MPSA06 and MPSA56, which are common TO-
92 parts, and which surely are not part of the heat-sink thermal-tracking system. The whole thing leaves one feeling like a great opportunity has somehow been missed.