OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 48)

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LEDset APPLICATIONS
3.5. Constant lumen output
The application example in chapter 3.3.2.5. Application
solution 4 – overtemperature management: microcontroller
approach shows that – in addition to the thermal manage-
ment of the module – more features can be added thanks
to the presence of the MCU:
• By using a general-purpose timer of the MCU, it is possible
to measure the working time of the module and store it to
memory.
• The real-time temperature measurement allows the appli-
cation of a “temperature weight” to properly estimate the
lifetime of the module.
• The knowledge of the real supply current of the LED mod-
ule allows the application of a “current weight” to properly
estimate the lifetime of the module.
Figure 50: Aging compensation: characteristic of concept.
By estimating the lifetime of the module with the mentioned inputs (estimation algo-
rithms are not within the scope of this application guide), it is possible to increase
the nominal output current of the ECG to a certain degree (up to its maximum limit)
by increasing the Vset control voltage, thus compensating the aging effects of the LED
module as shown by the orange line in fi gure 50 (the dashed gray line illustrates the
luminous fl ux decrement that occurs if the aging effects are not compensated).
The concept explained above can be implemented by storing a constant-lumen lookup
table in the MCU memory. By entering the working time of the module (e.g. in kHours),
it is possible to achieve the increase in Vset control voltage required to compensate the
aging effects of the LED module. The working time can be regularly saved in the MCU
memory (e.g. EEPROM), thus providing an accurate estimation of the lifetime.