The temperature is inferred by the voltage drop of the pseudo-substrate diode, when the source and gate are both zero volts and we pull the drain gently negative. More current then won't give more temperature signal. The fake-diode tempco is probably highest at low currents.
At 1 mA pulldown current (my Fluke on its diode range) I'm seeing about -1.6 volts on the drain of an EPC8004, and that drop has a tempco of close to 2 mV/K. That's a nice thermometer.
I'll adjust the 5 volt supply to set the ganfet power dissipation to around a watt maybe, and occasionally pulse the p-fet off to scope the temperature. The temp measurement could be very low duty cycle, say a millisecond of measurement every second or so.
Given a full millisecond to make the measurement, I could use 1 mA as the test current. I only need as long as it takes to charge the various capacitances.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.