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LEDs – Where to next?
Colin Beale | 14th April 2015 | LLFY Seminar Manchester
www.osram-os.com
LED efficiency and performance:
What are the limits?
Visible LED performance and efficiency
The influencing factors
– Power dissipated (PD) = Forward current (IF) x Forward Voltage (VF)
LED 'droop'
– Flux vs. LED forward current is not linear, what if it was?
Watts
Current
Chip
LED power dissipation…... (PD = IF x VF)
Internal quantum efficiency
– How efficient is the process inside the chip (at the junction) at 'converting'
electrons into photons?
Chip extraction efficiency
Package extraction efficiency
– How many photons can escape from the package without getting
internally reflected and absorbed by the chip and surrounding materials?
Spectral power distribution (SPD)
– How bright do our eyes perceive the emitted light to be?
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LLFY Manchester – April 2015 | OS S NE | CB
lumens
Package
– What proportion of the photons produced at the chip junction escape from
the chip without getting reabsorbed?
Chip theoretical limits:
Thin GaN (UX3)
175mA / mm2 TJ = 85°C 3000K CRI80
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LLFY Manchester – April 2015 | OS S NE | CB
Visible LED performance and efficiency
The influencing factors
– Power dissipated (PD) = LED forward current (IF) x Forward Voltage (VF)
LED 'droop'
– Flux vs. LED forward current is not linear, what if it was?
Watts
Current
Chip
LED power dissipation…... (PD = IF x VF)
Internal quantum efficiency
– How efficient is the process inside the chip (at the junction) at 'converting'
electrons into photons?
Chip extraction efficiency
Package extraction efficiency
– How many photons emitted from the chip can escape from the package
without getting absorbed by the chip and surrounding materials?
Spectral power distribution (SPD)
– How do our eyes perceive the emitted light?
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LLFY Manchester – April 2015 | OS S NE | CB
lumens
Package
– What proportion of the photons produced in the chip junction area escape
from the chip without getting reabsorbed?
Chip theoretical limits:
Thin GaN (UX3)
UX3 chip at 175mA / mm2 TJ = 85°C 3000K CRI80
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LLFY Manchester – April 2015 | OS S NE | CB
Forward Voltage (VF):
Approaching the theoretical limit
VF (350mA) V
Deep Blue UX3 chip at 350mA / mm2, TJ = 25°C
E(eV) = hc ÷ λ(m)
hc = 1.24 x 10-6
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OSRAM OS Press release
February 2015
“In view of the speed with which this
first step has been implemented, we
are confident that the improved
process can be transferred to
production by the summer of 2015. Any
further reductions in forward voltage
will then only be marginal owing to the
laws of physics."
Dr. Joachim Hertkorn – OSRAM OS
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LLFY Manchester – April 2015 | OS S NE | CB
LED 'droop'
WPE (%)
Impact of current density on efficiency at TJ = 25°C
Current density mA / mm2
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LLFY Manchester – April 2015 | OS S NE | CB
OSRAM OS Press release
September 2013
"Researchers at Osram Opto
Semiconductors have now been
able to demonstrate the physical
effect responsible for the decrease
in efficiency (droop) at typical
operating current densities........"
"This research provides
semiconductor experts in
academic institutes and in industry
with a plausible roadmap for
finding ways to suppress this
effect."
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LLFY Manchester – April 2015 | OS S NE | CB
www.osram-os.com
Cost per lumen
New LED package designs
The 5630 package
Where to next?
History
– Introduced as a backlighting LED for displays and TVs. Proliferated in lighting when
supply exceeded demand and soon became a 'lighting industry standard'
Package size and shape
– 5.6 x 3.0mm. Rectangular to suit display edge lighting
applications. Large surface area to produce even
light injection into light guides whilst keeping
LED numbers and costs low
Chip area vs. package area
– At best 1:22
Package construction
– Traditional over moulded silver plated lead frame with PPA or epoxy white outer
moulding. Phosphor filled Silicone for volume conversion
Package limitations
– Reflectivity of white outer moulding reduces impacting luminous flux and accelerating
lumen depreciation. Expensive due to volume of materials used
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QFN (Quad Flat No lead)
Next generation LED lighting packages
Why?
– White outer moulding can be eliminated to increase lifetime
– Reduces chip to LED surface area ratio
– Reduces LED package material cost
– Package extraction efficiency improved
– Minimises LED footprint for high packing density
What?
– DURIS S2
A 2016 package with the same performance as a 5630 but with
longer lifetime and lower cost
– DURIS S5 and S8
Multi chip 3030 and 5050 packages with single and
multiple chips
– SYNIOS 2720
An LED package for industrial and automotive
applications. Three chip sizes without changing
package footprint
– More to follow very soon.....
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LLFY Manchester – April 2015 | OS S NE | CB
QFN Multi chip packages
100 to 1800lm
Why?
– Minimise cost per lumen by reducing package cost – one package for
multiple chips
– Increase efficiency by driving chips at lower current,
particularly two chip versions
– Very cost effective alternative to small COB
– Works well with reflectors and certain optics
What
– DURIS S5:
3030 package: Two series or parallel connected chips
– DURIS S8:
5050 package: Six to ten series connected chips
– DURIS S10:
7070 package: 18 and 24 chip arriving very soon.....
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LLFY Manchester – April 2015 | OS S NE | CB
www.osram-os.com
Thank you for your time and attention
Enjoy your day!
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