Definitions of Ta and Tc
Rated maximum ambient temperature Ta:
The control gear standard IEC/EN 61347 contains no definition of Ta and its measurement for luminaire inbuilt control gear. For independent control gear, the luminaire standard applies.
Rated maximum case temperature Tc:
The definition according to the lamp control gear standard IEC/EN 61347 is: “highest permissible temperature which may occur on the outer surface (at the indicated place, if marked) under normal conditions and at the rated voltage or the maximum of the rated voltage range”
Importance of Ta and Tc
The ambient temperature Ta has a direct influence on the lifetime of electronic components. If the ambient temperature Ta is too high, the device cannot emit enough heat to the environment. This can result in so-called hotspots (points where the temperature concentrates). Hotspots in the air close to the components can lead to premature aging and failure of the devices. The lifetime of an LED driver is based on its ambient temperature. The case temperature Tc is the highest permissible temperature which may occur at the Tc point on the drive’s surface for safe operation.
Measurement of Ta and Tc
The ambient temperature is very difficult to measure. The measurement of the Tc temperature is easier and more reliable. As part of the design process, MOONS’ conducts measurements for both Ta and Tc and makes sure that both measurements meet the highest requirements. And the Tc is shown in datasheet like below picture. This allows the luminaire manufacturer to determine the expected lifetime of the control gear based on the Tc temperature which is easier to measure.
Position of the Tc point
Typically, the Tc point is placed directly above temperature and lifetime critical components (e.g. capacitor, coil, transformer, etc.). For more information please click the link: https://www.moonsindustries.com/c/led-drivers-a11
