In order to understand the dynamics of the LTZ1000 temperature regulation loop better in order to estimate the chip temperature response due to ambient temperature fluctuations, I am attempting to produce a model of the thermal impedance of the chip by fitting a Foster RC ladder (later transforming this to the equivalent Cauer filter) to the transient thermal impedance charateristics of the LTZ1000. The datasheet curves for the transient thermal impedance for the LTZ1000 are inconsistent (they indicate a junction to ambient thermal resistance of around 170C/W) with the tabulated thermal resistance (unless this is just the junction to case thermal resistance - the datasheet doesnt actually specify which thermal resistance junction to case or junction to ambient is specified.) Has anyone obtained transient cooling curves for the LTZ1000 to compare with the datasheet curves? Even a measurement of the junction to ambient temperature difference as a function of heater dissipation would be useful. Whilst monitoring the chip temperature when the heater is driven with a fixed power as used when measuring the transient thermal impedance is easily done by measuring the Vbe of the temperature sensing transistor Q2, monitoring the temperature of the LTZ1000 chip is a little tricky once the temperature regulation loop is closed as the temperature sensing transistor Q2 can no longer be used to sense chip temperature fluctuations. However the base emitter voltage of Q2 could perhaps be used for this. Bruce