Highly Accelerated Life Test of LED Power Taisuke Sueda
ASTR 2015, Sep 9 -‐ 11, Cambridge, MA
1
HALT HALT・・・ It is proposed along with the dedicated device in the 1980s as Highly Accelerated Life Test. It is referred to as Limit Test in IEC62506 issue. Combined stress of temperature and vibration ［temperature stress］ -100℃～＋200℃ Thermal change 60℃/min ［vibration stress］ Six axis broadband vibration
HALT coverage
Rate of accident cause ※ Findings of National Institute of Technology and Evaluation in JAPAN (NITE)
Other, 14%
Temperature, 40%
Humidity, 18%
VibraJon, 28%
HALT coverage Temperature and vibraJon accounts for nearly 70% of failure factor.
HALT is combined stress of temperature and vibration.
LED lighJng market
Growth is expected at 10% per annum
※http://www.ledsmagazine.com/articles/print/volume-9/issue-9/features/led-lighting-market-holds-steady-in-2012magazine.html
LifeJme of LED LifeJme of LED fluorescent lamps is 5 to 10 Jmes longer than the lifeJme of convenJonal fluorescent lamps ⇒ It also requires the high reliability in power supply. convenJonal fluorescent lamps
lifeJme 5
6000～12000 hours
LED fluorescent lamps
40000～50000 hours
Test sample 354mm 38.5mm
Power supply of LED fluorescent lamps Product SpecificaJons PFC E-‐cap
AC
PFC
6
Output E-cap
Back converter circuit
Circuit configuraJon
DC
outside dimension
38.5×26.2 ×354mm
mass
0.25kg
rated input
AC100～242V, 75VA,50/60Hz
rated output
DC195V,0.350A
ambient temperature
-20℃～35℃
InstallaJon condiJon of test sample
Air duct LED Power supply
Vibration table 7
SchemaJc diagram of a test system ・ Only LED power supply is installed in the test chamber HALT LED power supply
Data logger AC source
LED lamp 8
FuncJonal Test
To operate the sample in a stated test Jme, we search the Jming when the sample doesn’t work or the measurement value changes. controlling Measurement item acceleraJon pickup thermocouple ・ A/F (AcJve Filter) output voltage, Microcomputer output port voltage, control power voltage, and input and output voltage, current ・ temperature：8 points, Key components ・ acceleraJon (only at the Jme of the vibraJon stress test) ・ FuncJonal test is carried out by changing the input voltage to check the minimum operaJng voltage. （ Since the sample was started by 69V, go up the voltage from 69V ） A/F output voltage Microcomputer output port control power voltage input and output voltage, current
Normal signal(20℃,69Ｖ)
acceleraJon pickup
Results ・LED power supply has sufficient margin for the product specs to high temperature stress and vibraJon stress. ・Sample was destroyed by -‐40 ℃ for low temperature step stress. → RCA for destrucJon in low temperature stress LOW TEMPERATURE STEP STRESS HIGH TEMPERATURE STEP STRESS RAPID THERMAL TRANSITION VIBRATION STEP STRESS COMBINED STRESS TEST
LOL -‐30℃ LDL -‐40℃ UOL 120℃ UDL 160℃ -‐20℃⇔110℃ 5cycl correct operaJon VOL 60Grms VDL 65Grms OL 65Grms DL 70Grms
Electrical characterisJcs at 20℃ and -‐30℃
If the temperature is low, to ensure that the ripple of the A / F output voltage increases at startup. A/F output voltage Microcomputer output port control power voltage input and output voltage, current Normal signal at 20℃
Signal at -‐30℃
Electrical characterisJcs at -‐40℃ ・Ripple current is further increased. ・Large current is generated at the Jme of failure.
A/F output voltage Microcomputer output port control power voltage
Ripple current is further increased.
input and output voltage, current Expanding
Large current is generated at the Jme of failure. input currrent
Signal at -‐40℃
Temperature change at 20℃
20℃ ： temperature of each device increases with the lapse of Jme. 40
A/F transformer A/F FET Microcomputer
Temperature[℃]
35
PFC E-‐cap Diode bridge
30
Converter FET Converter transformer Thyristor
25
20
15
Power ON
Power OFF
10 0
100
200
300
400
500
600
Time [sec]
700
800
900
1000
Temperature change at -‐30℃
-‐30℃ ： Temperature of the PEC E-‐cap increases rapidly. -‐10 PEC E-‐cap A/F transformer A/F FET
Temperature[℃]
-‐15
Microcomputer PFC E-‐cap
-‐20
Diode bridge Converter FET
-‐25
Converter transformer Thyristor
-‐30
Power ON Power OFF
-‐35
-‐40 0
100
200
300
400
500
600
Time [sec]
700
800
900
1000
Temperature change at -‐40℃
-‐40℃ ： Temperature of the thyristor is irregularly rise. Temperature of other devices hardly rise. A/F transformer
-‐20
Thyristor
A/F FET Microcomputer
Temperature[℃]
-‐25
PFC E-‐cap Diode bridge
-‐30
Converter FET Converter transformer Thyristor
-‐35
-‐40
Power ON
-‐45
Power OFF
-‐50 0
100
200
300
400
500
600
Time [sec]
700
800
900
1000
Temperature change at 20℃
Returned to 20 ℃ : Temperature of the thyristor is irregularly rise. Temperature of other devices hardly rise. 40
A/F transformer A/F FET
Temperature[℃]
35
Thyristor
Microcomputer PFC E-‐cap Diode bridge
30
Converter FET Converter transformer
25
Thyristor
20
15
Power ON
10 0
100
200
300
400
500
600
Time [sec]
700
800
900
1000
Summary of temperature change
・-‐30℃ : Temperature of the PEC E-‐cap increases rapidly. ・-‐40℃ : Temperature of the thyristor is irregularly rise. Temperature of other devices hardly rise. 40
-‐10
A/F transformer
A/F transformer
PFC E-‐cap Diode bridge
30
Microcomputer PFC E-‐cap
-‐20
Converter FET Converter transformer
Diode bridge Converter FET
-‐25
Thyristor
25
A/F FET
-‐15
Microcomputer
35
Temperature[℃]
Temperature[℃]
A/F FET
Converter transformer Thyristor
-‐30
20
15
電源ON
Power ON Power OFF
-‐35
電源OFF
-‐40
10 0
100
200
300
400
500
600
700
Time [sec]
800
900
0
1000
100
200
300
400
40
Temperature[℃]
Temperature[℃]
Microcomputer PFC E-‐cap Diode bridge
-‐30
Converter FET Converter transformer Thyristor
-‐35
-‐40
Power ON
-‐45
Power OFF
-‐50 0
100
200
300
400
500
600
Time [sec]
700
800
900
1000
700
800
900
1000
A/F transformer
A/F FET -‐25
600
-‐30℃
20℃ A/F transformer
-‐20
500
Time [sec]
-‐40℃
700
800
900
1000
A/F FET 35
Microcomputer PFC E-‐cap Diode bridge
30
Converter FET Converter transformer
25
Thyristor
20
Power ON
15
10 0
100
200
300
Time [sec] 400
500
600
20℃
Summary of temperature change
・-‐30℃ : Temperature of the PEC E-‐cap increases rapidly. ・-‐40℃ : Temperature of the thyristor is irregularly rise. Temperature of other devices hardly rise. 40
-‐10
A/F transformer
A/F transformer
PFC E-‐cap Diode bridge
30
Microcomputer PFC E-‐cap
-‐20
Converter FET Converter transformer
Diode bridge Converter FET
-‐25
Thyristor
25
A/F FET
-‐15
Microcomputer
35
Temperature[℃]
Temperature[℃]
A/F FET
Converter transformer Thyristor
-‐30
20
15
電源ON
Power ON Power OFF
-‐35
電源OFF
-‐40
10 0
100
200
300
400
500
600
700
Time [sec]
800
900
0
1000
100
200
300
400
Temperature[℃]
Temperature[℃]
Microcomputer PFC E-‐cap Diode bridge
-‐30
Converter FET Converter transformer Thyristor
-‐35
-‐40
Power ON
-‐45
-‐50 0
100
200
300
400
Power OFF
LDL 500
600
Time [sec]
600
700
800
900
1000
700
800
900
1000
-‐30℃ 40
A/F transformer
A/F FET -‐25
500
Time [sec]
20℃ A/F transformer
-‐20
LOL
-‐40℃
700
800
900
1000
A/F FET 35
Microcomputer PFC E-‐cap Diode bridge
30
Converter FET Converter transformer
25
Thyristor
20
Power ON
15
10 0
100
200
300
Time [sec] 400
500
600
20℃
EsJmate of the destrucJon cause at low temperature
As a result of the degradaJon invesJgaJon, MOS FET of the PFC circuit has been destroyed. EsJmate of the destrucJon cause ① With decreasing temperature, decrease in electrostaJc capacity of the PFC E-‐cap and increase in ESR. ⇒ Ripple voltage increases. ② The breakdown voltage reducJon of MOS FET that is used for PFC circuit with decreasing temperature.
MOS FET was destroyed by the peak voltage over the breakdown voltage.
PFC E-‐cap AC 19
PFC
Back converter circuit
Output E-‐cap DC
Comparison of capacitor temperature properJes
・ There is no data less than -‐40℃ in the E-‐cap datasheet. ⇒I acquire the low temperature characterisJc of the capacitor using HALT. ・ E-‐cap capacitance is reduced by half at -‐40℃. ・ Film capacitor capacitance is reduced by 10% at -‐100℃. 20
Rate of change in capacitance [%]
Capacitance Cs[µF]
10
1
0.1 film capacitor
0.01
E-cap
0.001 -120
20
-100
-80
-60
-40 -20 0 Tempetarute[℃ ]
20
Capacitance
40
60
80
0 -20 -40
-60
film capacitor E-cap
-80 -100 -120
-100
-80
-60
-40 -20 0 Tempetarute[℃ ]
20
40
60
80
Rate of change in capacitance
Comparison of capacitor temperature properJes ・ ESR of E-‐cap is rapidly increased by the low temperature. ・ ESR of film capacitor at low temperatures is several Jmes of that at 20 ℃. 100000
10 film capacitor
film capacitor
E-cap
E-cap
1
1000
tanδ
ESR[Ω]
10000
0.1
100
0.01
10 1 -120
-100
-80
-60
-40 -20 0 Tempetarute[℃ ]
20
40
60
80
ESR（ Equivalent Series Resistance ） 21
0.001 -120
-100
-80
-60
-40 -20 0 Tempetarute[℃ ]
tanδ
20
40
60
80
DestrucJon margin improvement plan
To prepare two kinds of design improvement Sample Hardware and Soiware (1) Hardware improvement plan
Film capacitor is placed in parallel with the PFC E-‐cap to prevent a decline in electrostaJc capacity at low temperature PFC E-‐cap AC
Film capacitor
PFC
Output E-‐cap Back converter circuit
DC
(2) Soiware improvement plan I add to the program the algorithm to stop operaJon if the ripple voltage is detected to be mulJple Jmes over the set threshold, and prevent destrucJon of the MOS FET.
Result of hardware improvement Both LOL and LDL were greatly improved. Before improvement Hardware improvement LOL -30℃ -50℃ LDL -40℃ -100℃ Ripple is reduced by the film capacitor . （Ripple maximum voltage 582V⇒467V） 582V ⇒ 467V
23
Before improvement at -‐40℃
Aier hardware improvement at -‐40℃
Result of hardware improvement ・ Normal operaJon at -‐50 ℃ although ripple was increased ・ -‐60 ℃ in failure ⇒ Normal operaJon when return to the -‐50 ℃ ・From -‐70℃ to -‐100℃ in failure ⇒ Normal operaJon at -‐50 ℃
Signal at -‐50℃
24
Signal at -‐60℃
Result of soiware improvement Before improvement Software improvement LOL -30℃ -30℃ LDL -40℃ -80℃ ・ LDL was improved by soiware detecJon ・ The breakdown voltage of the MOS FET is further reduced at -‐80℃. OperaJon stopped Large current
25
Before improvement at -‐40℃
Aier soiware improvement at -‐40℃
Conclusions 1. LED power supply has sufficient margin for the product specs to high temperature stress and vibraJon stress. 2. Sample was destroyed by -‐40 ℃ for low temperature step stress. MOS FET of the PFC circuit has been destroyed. 3. MOS FET was destroyed by the peak voltage over the breakdown voltage. It is caused of increase of ripple voltage caused by the decrease in electrostaJc capacity of the PFC E-‐cap. 4. As the result of comparison of capacitor temperature properJes, E-‐cap rapidly changed properJes at temperatures below -‐40 degrees, although Film capacitor characterisJcs even at -‐100 ℃ was stable. 5. As the result of hardware improvement, both LOL and LDL were greatly improved. 6. As the result of soiware improvement, LDL was improved -‐80℃ from -‐40℃. 26
