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Electronic Design Verification Tests for LED Driver: Analysis and Implementation of Worst Case Tests
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Procedia Computer Science 00 (2019) 000–000 Available online at www.sciencedirect.com Procedia Computer Science 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Computer Science 158 (2019) 116–124
3rd World Conference on Technology, Innovation and Entrepreneurship (WOCTINE) 3rd World Conference on Technology, Innovation and Entrepreneurship (WOCTINE)
Electronic Design Verification Tests for LED Driver: Electronic Design Verification Tests for LED Driver: Analysis and Implementation of Worst Case Tests Analysis and Implementation of Worst Case Tests M. Caner Başol1,* , Ö. Emre Pepeç1, K. Yılmaz Kaya1, Murat Ayaz2 M. Caner Başol1,*, Ö. Emre Pepeç1, K. Yılmaz Kaya1, Murat Ayaz2 1
R&D Department, Akım Metal R&D Center, Istanbul 34459, Turkey of electric andMetal energy, University Kocaeli34459, 41001,Turkey Turkey R&D Department, Akım R&D Center,ofIstanbul 2 Deparment of electric and energy, University of Kocaeli 41001, Turkey 2 1 Deparment
Abstract Abstract Nowadays, LED (Light Emitting Diode) luminaires are beginning to dominate the lighting market with the increasing importance Nowadays, LEDas(Light Emittinglife Diode) luminairesThis are cause beginning to dominate the lighting withofthe increasing importance of features such cost, product and efficiency. to increase competition in the market production LED drivers and enforce of features suchtoasoffer cost,the product lifequality and efficiency. This to increase competition in the production of LED drivers enforce manufacturers highest product to thecause market at the lowest cost. Designs with low cost targets can and cause some manufacturers to system offer the highest quality product to the market at the lowest cost.InDesigns withitlow cost importance targets can to cause some problems such as instability and working in unsafe areas due to restrictions. this respect, is great complete problems such as system instability andbefore working unsafe come areas onto due tothe restrictions. respect, it is greattoimportance complete “Electronic Design Verification Tests” theinproduct market. In In thisthis study, it was aimed design andtoimplement “Electronic Verification Tests” product onto“Electronic the market. In this study, it was aimed to design anddrivers implement “The WorstDesign Case Situation Tests” forbefore LEDthe driver. In come addition, Design Verification Tests” for LED are “The Worstin Case mentioned detail.Situation Tests” for LED driver. In addition, “Electronic Design Verification Tests” for LED drivers are mentioned in detail. © 2019 The Author(s). Published by Elsevier B.V. © 2019 2019 The Published Elsevier B.V. © The Authors. Author(s). Publishedbyby B.V. committee of the 3rd World Conference on Technology, Innovation and Peer-review under responsibility of Elsevier the scientific Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship Entrepreneurship Entrepreneurship Keywords: LED driver, electronic design verification tests, life tests, accelerated life test, life prediction, the worst case tests, on–off tests, ageing tests,LED feilddriver, tests, PLC based design on-off verification setup Keywords: electronic tests, life tests, accelerated life test, life prediction, the worst case tests, on–off tests, ageing tests, feild tests, PLC based on-off setup
1. Introduction 1. Introduction In recent years, efforts to increase energy efficiency in lighting systems have accelerated. Especially with the In recent years, efforts to increase energy efficiency in LED lighting systems havehave accelerated. Especially with the development of semiconductor technology, high efficiency lighting systems been widely used. However, development of semiconductor technology, high efficiency LED lighting systems have been widely used. However, the high costs compared to traditional lighting systems, force LED driver manufacturers to produce high quality the high costs lightingproblems systems,such forceasLED driver manufacturers to produce highareas quality products at lowcompared cost [1,2].toIntraditional low cost design, system instability and working in unsafe are products at low cost [1,2]. In low cost design, problems such as system instability and working in unsafe areas are coming insight. coming insight. * Corresponding author. Mehmet Caner Basol *E-mail Corresponding author. Mehmet Caner Basol address: [email protected] E-mail address: [email protected] 1877-0509 © 2019 The Author(s). Published by Elsevier B.V. 1877-0509 2019responsibility The Author(s). Published bycommittee Elsevier B.V. Peer-review©under of the scientific of the 3rd World Conference on Technology, Innovation and Entrepreneurship Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship
1877-0509 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship 10.1016/j.procs.2019.09.034
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Fig. 1. “Electronic Design Verification Tests” for LED driver and flow chart
Therefore, “The Electronic Design Verification Tests” of LED driver are great importance. Target of these tests is detecting errors in the design of the LED driver or in the manufacturing process before submitted to end user. In this study, design validation tests are discussed and a programmable logic controller (PLC) based on-off test setup has been developed for “The Worst Case Tests”. “Electronic Design Verification Tests” consist of four tests: “Life Tests”, “The Worst Case Tests”, “Ageing Tests” and “Field Tests”. 2. Electronic Design Verification Tests for LED Driver 2.1. Life Tests In terms of competitive capacity, it is a crucial issue that LED drivers must have a sufficient lifetime. The designed product must reach the declared life time under certain conditions. Life tests are important for confirming the declared life time of products. Power supplies (SMPS, Switched Mode Power Supply) such as LED drivers; they consist of components such as switching element, diode, magnetic elements, resistance, MLCC (Multi Layer Ceramic Capacitor) and electrolytic capacitors. Among these components, the weakest link is the electrolytic capacitors due to its internal structure and this is shown in Figure-2 [3-4]. Therefore; the life of the electrolytic capacity determines the life of the product.
Fig. 2. The Weakset link at power supply: “Electrolytic Capacitors” [3]
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The answer of "Why do electrolytic capacitors determine the product life?" is the electrolytic fluid [3-4]. Thanks to this fluid, the desired capacitance value is reached in smaller volumes [3-4]. Reduction of fluid will reduce the capacitance value of the capacitor and increase the internal resistance of the ESR (Equivalent Series Resistance) which will cause it to overheat [3-4]. According to the literature; electrolytic capacitor life is completed when the ESR reaches a multiple of the nominal value, the leakage currents exceed a certain level or capacitance value decreases 80% of the nominal value [3].
Fig. 3. ESR – electrolytic liquid correlation [3]
2.1.1. Life Prediction for Electrolytic Capacitors : When calculating the life of the electrolytic capacitor, the formula in Equation-1 determined by the empirical tests and based on the "Arrhenius Rule" is used. This formula is used when the current exceeding the rated current is smaller than the rated current value [4]. 𝐿𝐿 = 2
𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − 𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶_𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 10
(1)
In the formula, the TRated parameter is the declared capacitor temperature while the TCap_Case parameter is the surface temperature at the top of capacitor. On condition that the current through capacitor is lower than the declared capacitor current; when the capacity temperature drops every 10°C, the life increases double (Arrhenius Rule). Accordingly, the capacitor of 105°C, 2000 hours; if the top surface temperature is 75°C, the life will be 16000 hours [4]. With this calculation, the appropriateness of the selected capacity is checked before the accelerated life test is performed. 2.1.2. Accelerated Life Test: The electrolytic capacitor which has the lowest life is determined with "Life Prediction of Electrolytic Capacitor Test". The stated capacitor is applied to the local heating and the lifetime is determined. Thereby the test is expedited by using the “Arrhenius Rule” (When the capacity temperature drops every 10°C, the life increases double). However, when the capacitor temperature increases to high levels, it causes the internal structure to deteriorate. For that reason, the local heating can be done up to a certain temperature [5]. Otherwise, the product life is incorrectly determined due to high temperature applied [5]. Figure-4 shows an experimental setup diagram for "Accelerated Life Test".
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Fig. 4. “Accelerated Life Test” setup diagram [5]
2.2. The Worst Case Tests Switching elements used in power supplies such as LED drivers; due to their structure, breakdown voltage and maximum current values change with temperature. Especially MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) have positive temperature coefficient. This means, breakdown voltage of MOSFET reduces with decreasing temperature [6]. Figure-5, shows “Breakdown Voltage–Junction Temperature” graphic of MOSFETs. According to this graphic, the MOSFET's breakdown voltage at -20°C decreases to 93% of the breakdown voltage at 25°C [6].
Fig. 5. “Breakdown Voltage–Junction Temperature” and “Drain Current–Case Temperature” graphics [6]
As shown in Figure-5, with the increase of temperature, maximum current of MOSFET is also decreased. For the silicon structure MOSFETs, when the higher voltage and current than can be applied; it becomes dysfunctional. LED driver is designed without considering the diminishing voltage and current values according to temperature, MOSFET failures may occur [7]. As for that magnetic elements are likely to get saturation at high temperature and high current [8]. For this reason, "The Worst Case Situation Tests" are important to verify the designed magnetic elements and used semiconductors.
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2.2.1. Continuous Working Test for Semiconductor and Magnetic Components at High Temperature and High/Low Input Voltage: LED drivers must operate at the declared high temperature and at high/low input voltage. The input voltage at which the LED driver operates at its most inefficient, is determined and the test is performed at the determined input voltage and high temperature. The semiconductors (MOSFET, diode etc...) and magnetic components used in the LED driver must be below the high temperature value in the datasheet (For semiconductor, junction temperature < 150°C) [6]. Thanks to this test; it is confirmed that the semiconductor and magnetic components remain in the safe zone under the declared conditions. 2.2.2. On-off Test at High Temperature and Low Input Voltage: LED drivers must operate at the declared high temperature and low voltage. The current passing through the MOSFET increases due to the current drawn from input at the low input voltage. However, the maximum current value of MOSFET decreases at high temperature [6]. Thanks to this test, MOSFET is tested under boundary conditions (High temperature and low voltage) by keeping it under transient response stress. It is also confirmed that magnetic elements will not be saturated by operating under the boundary conditions. By means of the designed on-off test device, the on-off condition is simulated. 2.2.3. On-off Test at Low Temperature and High Input Voltage: The voltage on the MOSFET is maximum level during off time at high input voltage and maximum load condition. In addition to this, breakdown voltage decreases with decreasing temperature. Thanks to test, MOSFET is tested under boundary conditions (High input voltage, maximum load and low temperature). With on-off test device, there are generated the oscillations on the input voltage and therefore on-off status is simulated. 2.2.4. On-off Test at Nominal Condition: The purpose of this test, which is longer than the other on-off tests, is to test varistor, fuse, capacitors and magnetic components by generating voltage stress. Especially, the protection elements such as fuse, varistor etc. are tested under high voltage oscillations and “In-rush” current at transient response. 2.3. Ageing Tests The LED driver is continuously tested under voltage pulses or by making sudden transitions between the declared temperature values (High and low temperature). The purpose of this test, is to test protection elements such as fuse, varistor, TVS (Transient Voltage Suppression) and semiconductors such as MOSFET, diode [9]. Figure-6 shows “Ageing Test Rack” of LINSUN Group for LED driver.
Fig. 6. LINSUN Group’s “Ageing Tests Rack” for LED drivers [9]
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2.4. Field Tests A great number of LED drivers is operated especially in harmonic zones. The objective is to test whether drivers are affected by the environment and each other while working. 3. On-off Test Device Implementation for The Worst Case Tests For “The Worst Case Tests” of “Electronic Design Validation Tests” on the LED drivers, the experimental setup which is called MCB OLYMPUS-1, was designed as shown in Figure-7. The MCB OLYMPUS-1 can be used up to 1500W and can operate in between 180 - 264 VRMS voltage range. The device is designed using Delta DVP-14SS and the input voltage and power are monitored by the SMB Technics branded energy analyzer. In addition, the number of LED driver is monitored by the energy analyzer. The device also has an “Emergency Stop” button to cut-off energy in case of emergency.
Fig. 7. MCB OLYMPUS-1, on-off test device
The flow diagram of control algorithm of “The Worst Case Tests” is shown in Figure-8. According to the flow diagram, in order to be able to start the test process, one of “The Worst Case Tests” must be selected. Then, the configuration values (On time, off time, number of cycle and ambient temperature) are determined according to LED driver features. Afterwards, the safety conditions must be provided. If the safety conditions are met, then test is started. The first cycle is performed according to the specified working period (On and off time) and the safety requirement is checked. If the safety conditions are not met, the safety conditions are met and the status of the test is determined. The test values determined in each cycle are recorded. When the runtime expires, the program ends.
Fig. 8. MCB OLYMPUS-1, control algorithm of “The Worst Case Tests”
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Before starting “The Worst Case Tests”, the functionality of the test device was examined. Figure-9 (Left side) shows the input voltage and current (In-rush current, cold start) of the SMB Technics branded Compact-B LED driver. It can be seen that the input voltage is up to 351 V PEAK and it also has an input in-rush current of 16.2 APEAK, 250 µs and the test device does not prevent in-rush current and transient voltage oscillations. Thanks to the on-off test device (MCB OLYMPUS-1), voltage oscillations and in-rush currents are generated at on-off transitions.
Fig. 9. LED driver input voltage, “In-rush Current” and SMB Technics branded Compact-B LED Driver Family (20W to 60W)
4. The Worst Case Tests Implementation and Results LED drivers must be designed to operate at between declared temperature values and input voltages without failure. By force of “The Worst Case Tests”, by LED drivers operate at limit values; design error and manufacturing error is determined. Thereby, the faults that will be encountered in the subsequent periods are determined during the design phase. In addition to this, ensures brand assurance and potential increase at the project costs is prevented [7]. ’Worst Case Tests” consist of four tests for LED drivers: • • • • times)
Continuous working tests at 50°C ambient temperature, 264 VRMS input voltage and full load (Min. 2 hours) On-off test at 50°C ambient temperature, 198 VRMS input voltage and full load (5000 times) On-off test at -20°C ambient temperature, 264 VRMS input voltage and full load (5000 times) On-off test at nominal condition (25°C ambient temperature, 230 VRMS input voltage) and full load (50000
SMB Technics branded Compact-B LED Driver Family (Power range is between 20W - 60W.) is used in these tests (Figure-9, right side).
Fig. 10. On-off test setup block diagram at high (50°C) and low temperature (-20°C)
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Fig. 11. On-off test setup block diagram at nominal condition
Figure-10 and Figure-11 show the setup for “The Worst Case Tests”. The desired temperature values, between 20°C / +50°C, is provided by the climate chamber. The input voltage is step-up or de step-down with a low UK value (Low leakage inductance) transformer. By this way, the inrush current is not suppressed. “The Continuous Working Test” for semiconductors and magnetic components at high temperature (50°C) and high voltage (264 VRMS) was completed for 4 hours. As a result of this test; The semiconductors and magnetic components used in the Compact-B LED drivers are below the temperature values specified in their datasheet (Such as semiconductor; junction temperature <150°C); remained in the safe zone (Figure-12).
Fig. 12. Compact-B LED 30W LED driver test results at 50°C and 264 VRMS input voltage
On-off test at high temperature (50°C) and low voltage (198 VRMS) was completed by 5000 times (Figure-13, left side). As a result of this test, no failure was encountered in the Compact-B LED drivers. It has been confirmed that driver designs are appropriate and that there are no faults. It has also been confirmed that the magnetic elements are not saturated.
Fig. 13. On-off test setup with climate chamber and on-off test setup at nominal condition
The on-off test at low temperature (-20°C) and high voltage (264 VRMS) was completed by 5000 times (Figure-13, left side). As a result of this test, no failure was encountered in the Compact-B LED drivers. It has been confirmed that driver designs are appropriate and that there are no faults.
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Figure-13 (Right side) shows the setup for the on-off test under nominal conditions (20°C and 230 VRMS). This test was completed by 50000 times and no failure was found in the Compact-B LED drivers. As a result of the test, it has been confirmed that the selected protection elements (fuse, varistor, etc.) as well as the input circuit structure have been designed properly. The Compact-B LED Driver Family has successfully completed the “The Worst Case Tests”. 5. Conclusion In this study, “Electronics Design Validation Tests” which are determined for LED drivers were taken into consideration and “The Worst Case Tests” which are the most important of “Electronic Design Verification Tests” have analyzed with the experimental studies. Also, the design of a PLC based on-off test devices (MCB OLYMPUS1) is performed successfully. In conclusion, all “The Worst Case Tests” have examined and implemented for SMB Technics branded Compact-B LED Driver Family and the test results have shared at end of the study. References [1] Steigerwald, D.A.; Bhat, J.C.; Collins, D.; Fletcher, R.M.; Holcomb,M.O.;Ludowise, M.J.; Martin, P.S.; Rudaz, Illumination with solid state lighting technology IEEE Journal of Selected Topics in Quantum ElectronicsVol. 8, Issue 2, March-April 2002 Pages: 310 - 320H. [2] https://www.businesswire.com/news/home/20161107005597/en/Turkey-Light-Emitting-Diodes-LEDs-Market-Report [3] V. Süel, H.A. Onay, M.K. Akıncı, T. Özgen, “Life Prediction of Aluminum Electrolytic Capacitors Used in Two-Level Inverters”, ICENTE Conference, 2018. [4] Maniktala, S., “Troubleshooting Switching Power Converters”. [5] L. Han, N. Narendran, “An Accelerated Test Method for Predicting the Useful Life of an LED Driver”, IEEE Transactions On Power Electronics, Vol. 26, No. 8, August 2011 [6] J. Dodge, Advanced Power Technology, “Power MOSFET Tutorial”, Application Note, APT-0403 Rev B, 2, March 2016. [7] R. Malik, R. Fishbune, IBM Corporation, “Why do Power Supplies Fail, and What can be done about it?”, 2005 [8] K. Billings and T. Morey, Switchmode Power Supply Handbook, New York, NY, USA: McGraw-Hill, 2011. [9] https://www.lisungroup.com/led-driver-aging-rack.html
ScienceDirect ScienceDirect
Procedia Computer Science 00 (2019) 000–000 Available online at www.sciencedirect.com Procedia Computer Science 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Computer Science 158 (2019) 116–124
3rd World Conference on Technology, Innovation and Entrepreneurship (WOCTINE) 3rd World Conference on Technology, Innovation and Entrepreneurship (WOCTINE)
Electronic Design Verification Tests for LED Driver: Electronic Design Verification Tests for LED Driver: Analysis and Implementation of Worst Case Tests Analysis and Implementation of Worst Case Tests M. Caner Başol1,* , Ö. Emre Pepeç1, K. Yılmaz Kaya1, Murat Ayaz2 M. Caner Başol1,*, Ö. Emre Pepeç1, K. Yılmaz Kaya1, Murat Ayaz2 1
R&D Department, Akım Metal R&D Center, Istanbul 34459, Turkey of electric andMetal energy, University Kocaeli34459, 41001,Turkey Turkey R&D Department, Akım R&D Center,ofIstanbul 2 Deparment of electric and energy, University of Kocaeli 41001, Turkey 2 1 Deparment
Abstract Abstract Nowadays, LED (Light Emitting Diode) luminaires are beginning to dominate the lighting market with the increasing importance Nowadays, LEDas(Light Emittinglife Diode) luminairesThis are cause beginning to dominate the lighting withofthe increasing importance of features such cost, product and efficiency. to increase competition in the market production LED drivers and enforce of features suchtoasoffer cost,the product lifequality and efficiency. This to increase competition in the production of LED drivers enforce manufacturers highest product to thecause market at the lowest cost. Designs with low cost targets can and cause some manufacturers to system offer the highest quality product to the market at the lowest cost.InDesigns withitlow cost importance targets can to cause some problems such as instability and working in unsafe areas due to restrictions. this respect, is great complete problems such as system instability andbefore working unsafe come areas onto due tothe restrictions. respect, it is greattoimportance complete “Electronic Design Verification Tests” theinproduct market. In In thisthis study, it was aimed design andtoimplement “Electronic Verification Tests” product onto“Electronic the market. In this study, it was aimed to design anddrivers implement “The WorstDesign Case Situation Tests” forbefore LEDthe driver. In come addition, Design Verification Tests” for LED are “The Worstin Case mentioned detail.Situation Tests” for LED driver. In addition, “Electronic Design Verification Tests” for LED drivers are mentioned in detail. © 2019 The Author(s). Published by Elsevier B.V. © 2019 2019 The Published Elsevier B.V. © The Authors. Author(s). Publishedbyby B.V. committee of the 3rd World Conference on Technology, Innovation and Peer-review under responsibility of Elsevier the scientific Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship Entrepreneurship Entrepreneurship Keywords: LED driver, electronic design verification tests, life tests, accelerated life test, life prediction, the worst case tests, on–off tests, ageing tests,LED feilddriver, tests, PLC based design on-off verification setup Keywords: electronic tests, life tests, accelerated life test, life prediction, the worst case tests, on–off tests, ageing tests, feild tests, PLC based on-off setup
1. Introduction 1. Introduction In recent years, efforts to increase energy efficiency in lighting systems have accelerated. Especially with the In recent years, efforts to increase energy efficiency in LED lighting systems havehave accelerated. Especially with the development of semiconductor technology, high efficiency lighting systems been widely used. However, development of semiconductor technology, high efficiency LED lighting systems have been widely used. However, the high costs compared to traditional lighting systems, force LED driver manufacturers to produce high quality the high costs lightingproblems systems,such forceasLED driver manufacturers to produce highareas quality products at lowcompared cost [1,2].toIntraditional low cost design, system instability and working in unsafe are products at low cost [1,2]. In low cost design, problems such as system instability and working in unsafe areas are coming insight. coming insight. * Corresponding author. Mehmet Caner Basol *E-mail Corresponding author. Mehmet Caner Basol address: [email protected] E-mail address: [email protected] 1877-0509 © 2019 The Author(s). Published by Elsevier B.V. 1877-0509 2019responsibility The Author(s). Published bycommittee Elsevier B.V. Peer-review©under of the scientific of the 3rd World Conference on Technology, Innovation and Entrepreneurship Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship
1877-0509 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 3rd World Conference on Technology, Innovation and Entrepreneurship 10.1016/j.procs.2019.09.034
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Fig. 1. “Electronic Design Verification Tests” for LED driver and flow chart
Therefore, “The Electronic Design Verification Tests” of LED driver are great importance. Target of these tests is detecting errors in the design of the LED driver or in the manufacturing process before submitted to end user. In this study, design validation tests are discussed and a programmable logic controller (PLC) based on-off test setup has been developed for “The Worst Case Tests”. “Electronic Design Verification Tests” consist of four tests: “Life Tests”, “The Worst Case Tests”, “Ageing Tests” and “Field Tests”. 2. Electronic Design Verification Tests for LED Driver 2.1. Life Tests In terms of competitive capacity, it is a crucial issue that LED drivers must have a sufficient lifetime. The designed product must reach the declared life time under certain conditions. Life tests are important for confirming the declared life time of products. Power supplies (SMPS, Switched Mode Power Supply) such as LED drivers; they consist of components such as switching element, diode, magnetic elements, resistance, MLCC (Multi Layer Ceramic Capacitor) and electrolytic capacitors. Among these components, the weakest link is the electrolytic capacitors due to its internal structure and this is shown in Figure-2 [3-4]. Therefore; the life of the electrolytic capacity determines the life of the product.
Fig. 2. The Weakset link at power supply: “Electrolytic Capacitors” [3]
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The answer of "Why do electrolytic capacitors determine the product life?" is the electrolytic fluid [3-4]. Thanks to this fluid, the desired capacitance value is reached in smaller volumes [3-4]. Reduction of fluid will reduce the capacitance value of the capacitor and increase the internal resistance of the ESR (Equivalent Series Resistance) which will cause it to overheat [3-4]. According to the literature; electrolytic capacitor life is completed when the ESR reaches a multiple of the nominal value, the leakage currents exceed a certain level or capacitance value decreases 80% of the nominal value [3].
Fig. 3. ESR – electrolytic liquid correlation [3]
2.1.1. Life Prediction for Electrolytic Capacitors : When calculating the life of the electrolytic capacitor, the formula in Equation-1 determined by the empirical tests and based on the "Arrhenius Rule" is used. This formula is used when the current exceeding the rated current is smaller than the rated current value [4]. 𝐿𝐿 = 2
𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − 𝑇𝑇𝐶𝐶𝐶𝐶𝐶𝐶_𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 10
(1)
In the formula, the TRated parameter is the declared capacitor temperature while the TCap_Case parameter is the surface temperature at the top of capacitor. On condition that the current through capacitor is lower than the declared capacitor current; when the capacity temperature drops every 10°C, the life increases double (Arrhenius Rule). Accordingly, the capacitor of 105°C, 2000 hours; if the top surface temperature is 75°C, the life will be 16000 hours [4]. With this calculation, the appropriateness of the selected capacity is checked before the accelerated life test is performed. 2.1.2. Accelerated Life Test: The electrolytic capacitor which has the lowest life is determined with "Life Prediction of Electrolytic Capacitor Test". The stated capacitor is applied to the local heating and the lifetime is determined. Thereby the test is expedited by using the “Arrhenius Rule” (When the capacity temperature drops every 10°C, the life increases double). However, when the capacitor temperature increases to high levels, it causes the internal structure to deteriorate. For that reason, the local heating can be done up to a certain temperature [5]. Otherwise, the product life is incorrectly determined due to high temperature applied [5]. Figure-4 shows an experimental setup diagram for "Accelerated Life Test".
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Fig. 4. “Accelerated Life Test” setup diagram [5]
2.2. The Worst Case Tests Switching elements used in power supplies such as LED drivers; due to their structure, breakdown voltage and maximum current values change with temperature. Especially MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) have positive temperature coefficient. This means, breakdown voltage of MOSFET reduces with decreasing temperature [6]. Figure-5, shows “Breakdown Voltage–Junction Temperature” graphic of MOSFETs. According to this graphic, the MOSFET's breakdown voltage at -20°C decreases to 93% of the breakdown voltage at 25°C [6].
Fig. 5. “Breakdown Voltage–Junction Temperature” and “Drain Current–Case Temperature” graphics [6]
As shown in Figure-5, with the increase of temperature, maximum current of MOSFET is also decreased. For the silicon structure MOSFETs, when the higher voltage and current than can be applied; it becomes dysfunctional. LED driver is designed without considering the diminishing voltage and current values according to temperature, MOSFET failures may occur [7]. As for that magnetic elements are likely to get saturation at high temperature and high current [8]. For this reason, "The Worst Case Situation Tests" are important to verify the designed magnetic elements and used semiconductors.
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2.2.1. Continuous Working Test for Semiconductor and Magnetic Components at High Temperature and High/Low Input Voltage: LED drivers must operate at the declared high temperature and at high/low input voltage. The input voltage at which the LED driver operates at its most inefficient, is determined and the test is performed at the determined input voltage and high temperature. The semiconductors (MOSFET, diode etc...) and magnetic components used in the LED driver must be below the high temperature value in the datasheet (For semiconductor, junction temperature < 150°C) [6]. Thanks to this test; it is confirmed that the semiconductor and magnetic components remain in the safe zone under the declared conditions. 2.2.2. On-off Test at High Temperature and Low Input Voltage: LED drivers must operate at the declared high temperature and low voltage. The current passing through the MOSFET increases due to the current drawn from input at the low input voltage. However, the maximum current value of MOSFET decreases at high temperature [6]. Thanks to this test, MOSFET is tested under boundary conditions (High temperature and low voltage) by keeping it under transient response stress. It is also confirmed that magnetic elements will not be saturated by operating under the boundary conditions. By means of the designed on-off test device, the on-off condition is simulated. 2.2.3. On-off Test at Low Temperature and High Input Voltage: The voltage on the MOSFET is maximum level during off time at high input voltage and maximum load condition. In addition to this, breakdown voltage decreases with decreasing temperature. Thanks to test, MOSFET is tested under boundary conditions (High input voltage, maximum load and low temperature). With on-off test device, there are generated the oscillations on the input voltage and therefore on-off status is simulated. 2.2.4. On-off Test at Nominal Condition: The purpose of this test, which is longer than the other on-off tests, is to test varistor, fuse, capacitors and magnetic components by generating voltage stress. Especially, the protection elements such as fuse, varistor etc. are tested under high voltage oscillations and “In-rush” current at transient response. 2.3. Ageing Tests The LED driver is continuously tested under voltage pulses or by making sudden transitions between the declared temperature values (High and low temperature). The purpose of this test, is to test protection elements such as fuse, varistor, TVS (Transient Voltage Suppression) and semiconductors such as MOSFET, diode [9]. Figure-6 shows “Ageing Test Rack” of LINSUN Group for LED driver.
Fig. 6. LINSUN Group’s “Ageing Tests Rack” for LED drivers [9]
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2.4. Field Tests A great number of LED drivers is operated especially in harmonic zones. The objective is to test whether drivers are affected by the environment and each other while working. 3. On-off Test Device Implementation for The Worst Case Tests For “The Worst Case Tests” of “Electronic Design Validation Tests” on the LED drivers, the experimental setup which is called MCB OLYMPUS-1, was designed as shown in Figure-7. The MCB OLYMPUS-1 can be used up to 1500W and can operate in between 180 - 264 VRMS voltage range. The device is designed using Delta DVP-14SS and the input voltage and power are monitored by the SMB Technics branded energy analyzer. In addition, the number of LED driver is monitored by the energy analyzer. The device also has an “Emergency Stop” button to cut-off energy in case of emergency.
Fig. 7. MCB OLYMPUS-1, on-off test device
The flow diagram of control algorithm of “The Worst Case Tests” is shown in Figure-8. According to the flow diagram, in order to be able to start the test process, one of “The Worst Case Tests” must be selected. Then, the configuration values (On time, off time, number of cycle and ambient temperature) are determined according to LED driver features. Afterwards, the safety conditions must be provided. If the safety conditions are met, then test is started. The first cycle is performed according to the specified working period (On and off time) and the safety requirement is checked. If the safety conditions are not met, the safety conditions are met and the status of the test is determined. The test values determined in each cycle are recorded. When the runtime expires, the program ends.
Fig. 8. MCB OLYMPUS-1, control algorithm of “The Worst Case Tests”
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Before starting “The Worst Case Tests”, the functionality of the test device was examined. Figure-9 (Left side) shows the input voltage and current (In-rush current, cold start) of the SMB Technics branded Compact-B LED driver. It can be seen that the input voltage is up to 351 V PEAK and it also has an input in-rush current of 16.2 APEAK, 250 µs and the test device does not prevent in-rush current and transient voltage oscillations. Thanks to the on-off test device (MCB OLYMPUS-1), voltage oscillations and in-rush currents are generated at on-off transitions.
Fig. 9. LED driver input voltage, “In-rush Current” and SMB Technics branded Compact-B LED Driver Family (20W to 60W)
4. The Worst Case Tests Implementation and Results LED drivers must be designed to operate at between declared temperature values and input voltages without failure. By force of “The Worst Case Tests”, by LED drivers operate at limit values; design error and manufacturing error is determined. Thereby, the faults that will be encountered in the subsequent periods are determined during the design phase. In addition to this, ensures brand assurance and potential increase at the project costs is prevented [7]. ’Worst Case Tests” consist of four tests for LED drivers: • • • • times)
Continuous working tests at 50°C ambient temperature, 264 VRMS input voltage and full load (Min. 2 hours) On-off test at 50°C ambient temperature, 198 VRMS input voltage and full load (5000 times) On-off test at -20°C ambient temperature, 264 VRMS input voltage and full load (5000 times) On-off test at nominal condition (25°C ambient temperature, 230 VRMS input voltage) and full load (50000
SMB Technics branded Compact-B LED Driver Family (Power range is between 20W - 60W.) is used in these tests (Figure-9, right side).
Fig. 10. On-off test setup block diagram at high (50°C) and low temperature (-20°C)
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Fig. 11. On-off test setup block diagram at nominal condition
Figure-10 and Figure-11 show the setup for “The Worst Case Tests”. The desired temperature values, between 20°C / +50°C, is provided by the climate chamber. The input voltage is step-up or de step-down with a low UK value (Low leakage inductance) transformer. By this way, the inrush current is not suppressed. “The Continuous Working Test” for semiconductors and magnetic components at high temperature (50°C) and high voltage (264 VRMS) was completed for 4 hours. As a result of this test; The semiconductors and magnetic components used in the Compact-B LED drivers are below the temperature values specified in their datasheet (Such as semiconductor; junction temperature <150°C); remained in the safe zone (Figure-12).
Fig. 12. Compact-B LED 30W LED driver test results at 50°C and 264 VRMS input voltage
On-off test at high temperature (50°C) and low voltage (198 VRMS) was completed by 5000 times (Figure-13, left side). As a result of this test, no failure was encountered in the Compact-B LED drivers. It has been confirmed that driver designs are appropriate and that there are no faults. It has also been confirmed that the magnetic elements are not saturated.
Fig. 13. On-off test setup with climate chamber and on-off test setup at nominal condition
The on-off test at low temperature (-20°C) and high voltage (264 VRMS) was completed by 5000 times (Figure-13, left side). As a result of this test, no failure was encountered in the Compact-B LED drivers. It has been confirmed that driver designs are appropriate and that there are no faults.
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Figure-13 (Right side) shows the setup for the on-off test under nominal conditions (20°C and 230 VRMS). This test was completed by 50000 times and no failure was found in the Compact-B LED drivers. As a result of the test, it has been confirmed that the selected protection elements (fuse, varistor, etc.) as well as the input circuit structure have been designed properly. The Compact-B LED Driver Family has successfully completed the “The Worst Case Tests”. 5. Conclusion In this study, “Electronics Design Validation Tests” which are determined for LED drivers were taken into consideration and “The Worst Case Tests” which are the most important of “Electronic Design Verification Tests” have analyzed with the experimental studies. Also, the design of a PLC based on-off test devices (MCB OLYMPUS1) is performed successfully. In conclusion, all “The Worst Case Tests” have examined and implemented for SMB Technics branded Compact-B LED Driver Family and the test results have shared at end of the study. References [1] Steigerwald, D.A.; Bhat, J.C.; Collins, D.; Fletcher, R.M.; Holcomb,M.O.;Ludowise, M.J.; Martin, P.S.; Rudaz, Illumination with solid state lighting technology IEEE Journal of Selected Topics in Quantum ElectronicsVol. 8, Issue 2, March-April 2002 Pages: 310 - 320H. [2] https://www.businesswire.com/news/home/20161107005597/en/Turkey-Light-Emitting-Diodes-LEDs-Market-Report [3] V. Süel, H.A. Onay, M.K. Akıncı, T. Özgen, “Life Prediction of Aluminum Electrolytic Capacitors Used in Two-Level Inverters”, ICENTE Conference, 2018. [4] Maniktala, S., “Troubleshooting Switching Power Converters”. [5] L. Han, N. Narendran, “An Accelerated Test Method for Predicting the Useful Life of an LED Driver”, IEEE Transactions On Power Electronics, Vol. 26, No. 8, August 2011 [6] J. Dodge, Advanced Power Technology, “Power MOSFET Tutorial”, Application Note, APT-0403 Rev B, 2, March 2016. [7] R. Malik, R. Fishbune, IBM Corporation, “Why do Power Supplies Fail, and What can be done about it?”, 2005 [8] K. Billings and T. Morey, Switchmode Power Supply Handbook, New York, NY, USA: McGraw-Hill, 2011. [9] https://www.lisungroup.com/led-driver-aging-rack.html