LED temperature protection
AN2531
16/40
7 LED
temperature
protection
The STEVAL-009V1 was designed for high power RGB LEDs with a nominal power even
higher then ten watts. As the lifetime of LEDs significantly decreases with temperature, the
proper temperature management must be implemented to check and limit its maximum
values.
Two different temperature protections are used in this design as shown in
- the
STLM20 temperature sensor and NTC (negative temperature coefficient) resistor. The
STEVAL-ILL009V3 uses an NTC resistor directly assembled on the aluminum LED board
(OSTAR projection module). The STEVAL-ILL009V4 has assembled the STLM20
temperature sensor in the middle of LEDs on the PCB. The microcontroller checks the
voltage from the sensors and sets the correct output PWM signal on the OE pin of the LED
drivers. The microcontroller can increase the duty cycle of the PWM signal (0% duty cycle is
max bright and 100% duty cycle is no bright) or can turn OFF the RGB LED if over
temperature occurs. Software implementation is up to designers. Temperature protection
calculation using the STLM20 or NTC is presented in
.
Figure 10.
Temperature protection
AM00293
STEVAL - ILL009V4
STEVAL - ILL009V3
STLM20
Micro
ADC
Vc
R
NTC
