Three-pole devices

Bipolar transistors are three pole devices, where the power step is applied by changing the collector-base voltage and temperature change is detected by measuring the emitter-base voltage at constant current which can be high. MOSFETs are measured in a similar way.

The preferred method of transient measurement is measuring cooling off. In case of heating up, the power level changes all the time on the emitter-base junction, due to the diminishing voltage level. This is actually the effect, which we use for measurement. In case of three-pole devices, this causes only a small (1%) error.

• The calibration can be done with the T3Ster equipment and a cold-plate, for example.
• Set the lowest required temperature on the cold plate.
• Choose a proper parameter setting for a calibration process where the junction temperature does not differ from the cold-plate temperature. Program the T3Ster equipment for a low U_CB voltage value (i.e. 1V).
• Program the T3Ster equipment for the current you want to use. Set the powering to and set the Single Voltage Measurement panel to Pulsed setting. Compensate the used channel in the Set Measurement Channel panel to High.

  With these settings you can measure the high current/low temperature combination. If powering is set to then Pulsed means that the diode works at low current for 1s and then at high current for a very short (about 100µs) measurement series. The low U_CB value keeps your device in normal active state also without generating much dissipation.

• Read the forward voltage in the Single Voltage Measurement panel.
  

• Set the next required temperature on the cold plate. Read the forward voltage in the Single Voltage Measurement panel. As the highest possible forward voltage was measured at the lowest temperature, usually no further channel compensation is required.
  

If you measure devices of high backlash (like some MOSFETs), you may have problems with compensating the channel in Pulsed state. In this case use the and DC setting, i.e. apply steady power for a short time, compensate the channel and then switch to Pulsed. You may correct the compensation by shifting the measured value to the high end of the range if needed.