Figure 6-6: Preferred circuit arrangement for diodes (common cathode)
In case of measuring diodes the power excitation is applied to the same element where the thermal transient will be measured. In heating-up transients the fixed forward current causes decreasing power excitation due to the decrease of the forward voltage on the diode (the voltage which is actually used for temperature sensing). This effect causes problems in interpreting heating-up transients.
In the subsequent example a cooling-off transient of a small power diode will be measured. With no external cooling a quite fast thermal transient can be expected.
Unlike the transistor measurement the power steps will be relatively small (maximum 1.5 – 2 W). The maximum current rating of the diode should not be exceeded. The measurement can be implemented as described in Table 6-2.
The software provides graphical help at the configuration selection (Figure 6-7) to establish the proper connections between the T3Ster Main System Unit and the diode under test.
Figure 6-7: Help window in the measurement control software (diode measurement,
common cathode)