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The important of Ta, Tc, Tj & Ts for LED driver and luminaires


The important of Ta, Tc, Tj & Ts for LED driver and luminaires

All of the led lighting and control products have ratings that are dependent on temperature. you many see something like Ta, Tc and Tj on the products. Most of the customers don't understand what these rating mean.

Here is a brief summary of these ratings:

1. Definitions for ta and tc

1.1 Rated maximum ambient temperature ta :

The control gear standard IEC/EN 61347 contains no definition of ta and its measurement for luminaire built-in control gear.

For independent control gear the luminaire standard applies.

The luminaire standard requires the marking of the rated maximum ambient temperature ta, if other than 25 °C.

1.2 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". 

1.3 Rated maximum junction temperature tj:

Junction temperature, short for transistor junction temperature, is the highest operating temperature of the actual semiconductor in an electronic device. In operation, it is higher than case temperature and the temperature of the part's exterior.

1.4 Rated maximum soldering temperature ts:

The ts is defined as the soldering point temperature on LEDs. LED manufacturers design the ts on the LEDs, essentially for the COB LEDs, which allows the luminaries manufacturers to design the heat dissipation according to the maximum temperature. Ts has related to the Tj of the LEDs, which there is a calculation but differs on different LEDs.

 2. Difference between tc, ta, tj and ts

2.1 Ta= ambient temperature:

The temperature range of the air surrounding the electronic control gear declared by the manufacturer

2.2 Tc case temperature:

The temperature of a reference point on the control gear housing.

2.3 Tj junction temperature

The LED operating junction temperature

2.4 Ts soldering point temperature

The soldering point temperature for luminaries heat dissipation checking and quality control.

3. Importance of ta, tc, tj and ts

The ambient temperature ta has 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 a control gear is based on its ambient temperature.

The case temperature tc is the highest permissible temperature which may occur at the tc point on the control gear housing for safe operation.This is the temperature of the device circuit itself under given conditions. 

Tj must be calculated from the Ts. TJmax = Maximum Junction temperature. This is the maximum temperature that the device tolerate.

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