OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 42)

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3.3.2.5. Application solution 5 – overtemperature
management: microcontroller (MCU) approach
Since the cost of small 8-bit microcontrollers has dropped
over the past years, they have become an affordable solution
for implementing simple functionalities and increasing the
fl exibility of a system at the same time. These microcon-
trollers are equipped with various kinds of peripherals, e.g.
A/D converters (8–10 bits), which allow the measurement of
analog input coming from an NTC, as well as a light sensing
circuit. I2C or UART-embedded HW peripherals allow ex-
changing data via a communication bus or interfacing other
ICs (e.g. light sensors such as SFH7770 can be directly con-
nected via I2C bus).
In terms of temperature/overtemperature management,
this type of MCU (e.g. Microchip PIC12F1822 or Atmel
Tiny25/45) offers a high level of fl exibility as it can be
programmed to achieve different goals:
Different NTC sensors can be interfaced by saving different
NTC characteristics in the MCU memory.
• The NTC signal can be “transformed” into Vset output (and
therefore Iout) via a very fl exible and fully customizable relation.
• Some MCUs, e.g. the types mentioned on the left, have an
embedded temperature sensor which can be used to eval-
uate the temperature of the LED module. In this way, it is
possible to save MCU resources/pins for other functions
such as sensing inputs.
• Information on the LED module and the luminaire, e.g.
current temperature value, set-up parameters and warning
temperature, can be communicated to the user in various
smart ways: via digital bus (by wire), by infrared receiver
and transmitter or by using an LED coding approach (e.g.
turning a dedicated LED on and off at a certain frequency).
• The LED module itself can be used to warn the user in
advance of a possible overtemperature problem. For this
purpose, the LED module can be put into “blinking” mode
by turning the light on and off or switching it between its
maximum and minimum level (see fi gure 43).
This MCU approach is illustrated by the schematic diagram
on the right.
LEDset APPLICATIONS