Sensor-less LED temperature sensing
Tunable Dimmable White
How to mimic accurately the light bulb with LED
Three must haves:
1. Follow exactly the Black Body radiation curve
2. Logarithmic correction for eye sensitivity when dimming
3. Accurate correction of temperature effects on LED performance
Tunable Dimmable White
1. Follow exactly the Black Body Radiation curve
R+G+B LEDs
R+G+B+A LEDs
- Missing white color points
- All color points, but expensive
Tunable Dimmable White
1. Follow exactly the Black Body Radiation curve
W+R LEDs
- Cannot follow Planckian curve
W+A LEDs
- Best trade-off
Chosen solution
Tunable Dimmable White
2. Logarithmic correction for eye sensitivity
Correlated Color Temperature (CCT) vs. dimming level
Incandescent lamp
Analytical CCT
Normalized light intensity
(b)
Δu’v’
CCT (K)
(a)
Noticeable limit
Normalized light intensity
Analytical model for CCT vs. Flux implemented in control model,
follow within the noticeable limit the incandescent lamp
Sensor-less LED Tj sensing for optimal color & flux
3. Accurate correction of T effects on LED performance
Conventional method
sensors
Drive currents
Thermal modeling
Compensation calc.
• Expensive (sensors, wirings,
computational power)
• Too slow
• Inaccurate
• dependent on heat sink
• dependent on operating conditions
Smart LED driver provides colour and light output stability at any temperature and age
NXP method
force
sense
Drive currents
20+ patent filings
Tj determination
LED control model
• No external sensor
• No extra wirings
• Fast (20 µs demonstrated)
• Accurate (~ 1°C res.)
• Enables dynamic light control
• Independent on heat sink
• Independent on operating conditions
• No need for thermal modeling
• Self-calibrating for aging compensation
Tunable Dimmable White
Summary
(a)
(b)
Yellow/Amber
Phosphor
Yellow/Amber
Phosphor
Blue LED
Blue LED
►
Amber LED
Amber LED
“Conventional way”:
 White + Red LEDs, “wrong” colors when
dimming
►
NXP differentiating solution:
 White + Amber LEDs
 Sensor-less LED Tj sensing
 Follow exactly the black body radiation curve
 Unique solution for color dimming down to
1% bulb equivalent