Transcript Nieizotermiczne charakterystyki impulsowych układów zasilających

The Influence of the Mounting
Manner of the Power LEDs on
Its Thermal and Optical
Parameters
Krzysztof Górecki, Przemysław Ptak
Gdynia Maritime University
Department of Marine Electronics
Outline
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Introduction
The measurement set to measure thermal and
optical parameters of power LEDs
Investigated structures of power LEDs
Results of measurements
Conclusions
Introduction (1)
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Power LEDs are more and more frequently used in the
lighting technique.
Within last twenty years there has been observed
essential improvement of exploitive parameters of
considered class of semiconductor devices and a
decrease in their price.
In numerous publications both properties of single
LEDs and LED lamps are considered.
As the great advantage of solid-state light sources
seems to be long life time, the essential problem is to
remove heat generated in the considered devices.
In order to assure long life time it is indispensable to
take efficient cooling of power LEDs.
Introduction (2)
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Thermal properties of semiconductor devices, e.g.
power LEDs, are characterized by the transient
thermal impedance Zth(t) and the thermal resistance
Rth.
The waveform of Zth(t) depends on the construction
of the case of the semiconductor device and on
elements improving cooling, such as heat-sinks.
In this paper the measurement set to measure
optical and thermal parameters of power LEDs and
the obtained results of measurements illustrating the
influence of the selection of the cooling system of
these LEDs on the considered parameters, are
presented.
The measurement set to measure thermal
and optical parameters of power LEDs
Polarisation and control circuit
D1
D2
DUT1
DUT2
S1
IH
IM
IM1
Instrumentation amplifiers
luxmeter
A/D converter module
PC
Investigated structures of power
LEDs
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Using the measurement set presented in the previous section, the
measurements of thermal, optical and electric parameters of many
types of power LEDs operating at different cooling conditions are
performed.
Investigations were made for LEDs situated in the case TO-220, in the
case EMITTER and in the case STAR.
The power dissipated Ptot of examined diodes contains the values within
the range from 1 to 5 W, and the maximum value of the forward current
IFmax - from 0.35 to 1.4 A.
The obtained luminous flux FV has values from 51.6 to 340 lm, at the
admissible value of the internal device temperature Tjmax from 120 to
135oC.
The examined power LEDs are installed in turn on two different heatsinks of the dimensions 175x118x8 mm (the large heat-sink) and of the
dimensions 100x75x2 mm (the small heat-sink).
Results of measurements
parameter
LED on small
heat-sink
LED on large
heat-sink
Rth [K/W]
37.4
13.31
8.91
a1
0.17
0.332
0.221
35
tth1 [s]
480.25
896.55
2062
30
a2
0.459
0.167
0.045
25
tth2 [s]
84.53
346
197.25
20
a3
0.102
0.095
0.382
tth3 [s]
17.32
5.12
2.353
a4
0.154
0.289
0.309
tth4 [s]
1.855
0.999
0.588
a5
0.053
0.057
0.039
tth5 [s]
0.3
0.152
0.0387
a6
0.029
0.044
0.004
tth6 [ms]
38.76
31.09
19.34
a7
0.033
0.016
tth7 [ms]
5.92
6.98
45
40
Zth(t) [K/W]
LED without
any heat-sink
OF-HPWW-5SL
P = 5W
LED without heat-sink
LED on small heat-sink
15
10
LED on large heat-sink
5
0
0,0001
0,001
0,01
0,1
1
t [s]
10
100
1000
10000
Results of measurements (2)
6000
6000
LED on large heat-sink
5000
4000
LED on small heat-sink
4000
3000
E [lx]
E [lx]
OF-HPWW-5SL
5000
LED without heat-sink
2000
LED on large heat-sink
LED on small heat-sink
3000
LED without heat-sink
2000
OF-HPWW-5SL
P = 5W
1000
1000
0
0
0,1
1
10
t [s]
100
1000
10000
0
200
400
600
800
ID [mA]
1000
1200
1400
Results of measurements (3)
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Mutual thermal interactions
3 diodes on the small heat-sink
12000
10
sum
9
7
5
4
6000
D3 (5 W)
4000
3
Zth12(t)
2
1
0
0,0001
D1 + D 2 + D 3
8000
6
E [lx]
Zth(t) [K/W]
10000
Zth11(t)
8
2000
Zth13(t)
0,001
0,01
0,1
1
t[s]
10
D2 (3 W)
D1 (1 W)
0
100
1000
10000
0
500
1000
1500
t [s]
2000
2500
Conclusions
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From the presented results of investigations it
results that self-heating phenomena and the
mutual thermal coupling between the diodes
situated on the common heat-sink influence not
only a change of the internal temperature
values of the considered devices, but also
cause essential depreciation of illuminance.
In the extreme case, as result of thermal
phenomena, one observes a decrease in the
value of illuminance at an increase of the
forward current of the examined LEDs.
Conclusions (2)
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It is also worth underlining that as a result of
thermal phenomena, time indispensable to
obtain the steady state value of optical
parameters of power LEDs can be very long,
even up to 2 hours.
The worked out by the authors measurement
set can be useful for designers of solid-state
light sources on the stage of testing efficiency
of the designed cooling system and testings
efficiency of the brightness control circuit.