How Electrolytic Capacitors Effect the Reliability of LED Drivers

Electrolytic capacitors in LED drivers

In 2008, MEAN WELL released their first LED driver, the CLG-150 series and took their first steps into the new and unknown LED lighting market.

  

Mean Well CLG-150-12 LED driver

MEAN WELL has since sold an immeasurably large number of LED drivers. Recently, an opportunity arose for MEAN WELL to receive back several of the CLG-150 LED drivers, which were manufactured in 2008. A detailed investigation and analysis were executed, and the result is shared below. 

The number of the components used in a single LED driver can vary from dozens to hundreds, depending on the power output and topology of the LED driver.   

A critical part of the design process is working out the exact lifetime of each components to evaluate its reliability. The expected lifetime of the LED driver is determined by the quality of its critical components, especially fans and electrolytic capacitors. In order to provide an accurate assessment of the LED driver’s lifetime, the MEAN WELL design must pass recognised verification processes including ORT (ongoing reliability), DMTBF (demonstrated mean time between failures), thermal shock testing…etc. 

In this article we will focus on the verification and evaluation of the electrolytic capacitors’ lifetime.  

Aluminium electrolytic capacitors can be affected by operation conditions such as temperature and load. After a long period of operation, the capacitance will reduce and the dissipation factor (tanδ) will increase, eventually effecting the lifetime. This phenomenon is called the diffusion effect, which means the electrolyte diffuses into the sealing material, eventually spread externally.  

Normally, the lifetime of the aluminum electrolytic capacitor can be evaluated by using the law of Arrhenius (reaction rate of chemical diffusion). The electrolyte dries up after a period of operation, causing the capacitance to reduce and the equivalent series resistance (ESR) to increase. The lifetime can be decreased by 50% when the ambient temperature rises 10℃. In contrast, if the temperature drops 10℃, the lifetime can be doubled. 

The relation between lifetime & failure rate is demonstrated in the following tube curve chart: 

LED driver tube curve chart

Initial Malfunction Period 

In order to avoid the initial malfunction period, MEAN WELL identifies any defective components by carrying out a 100% burn in test. As a result, most LED drivers sold by MEAN WELL will already in the accidental malfunction period. 

Accidental Malfunction Period 

The LED driver’s stability and reliability are related to the MTBF (meantime between failure). The failure rate is quite low in this period, and is determined by the user’s installation and operation conditions (ambient temperature, derating, air flow, vibration…etc.). 

Consumption Malfunction Period 

Following the accidental malfunction period, LED drivers move into the consumption malfunction period, during which, most failures are related to components aging, such as fans and capacitors. 

As mentioned above, a failure during the accidental malfunction period is related to the user’s installation and application conditions. Factors such as ambient temperature, derating, ventilation, violation…etc. Are usually the root cause of the failure of the LED driver. 

From here, our discussion focuses on the relationship between the ambient / case temperature, load condition and lifetime. 

MEAN WELL uses a method from a well-known electrolytic capacitor manufacturer to execute a product’s lifetime verification. For example, the CLG-150 series LED driver is fully potted, the output stage is designed with a 10000 hours / 105℃ electrolytic capacitor from a renowned Japanese brand. The lifetime vs load vs temperature is explained as below. 

Relation Between Usage Lifetime, Load, and Ambient Temperature 

With the relationship between lifetime and load, when the ambient temperature is 55℃ and the load is operated at 100% the lifetime is about 35Khrs. However, if the load is reduced to 75%, then the lifetime can be 1.6 times longer. 

With the relation between lifetime and ambient temperature, when the load is at 75% and the ambient temperature is 55℃, the lifetime is about 57Khrs. If the ambient temperature is reduced to 45℃, then lifetime will be doubled (114Khrs). 

These relationships are illustrated in the following chart: 

Electrolytic capacitor life time vs temperature chart

Relationship Between Usage lifetime and Case Temperature 

The potting compound used in the CLG-150 LED drivers makes it difficult to measure the internal temperature of the capacitor. Therefore, the external case temperature is used instead. If the case temperature is less than 55℃, the lifetime is about 100Khrs. However, when the case temperature rises to 70℃, the lifetime reduces to 35Khrs, as shown in the below graph: 

Electrolytic capacitor usage lifetime vs case temperature graph

Analysis of Electric Performance and Reliability 

Analysis of the electrical performance of CLG-150 LED driver, which has been used for 10 years on a street lighting application, was conducted to analyse the driver’s electrical performance and reliability. The main abstract of this analysis is shown below. 

Analysis of Electric Performance – Main Specifications 

Critical Electrical Parameter

Electrical Specification

Actual Value Measured

Efficiency

89%

90.1%

Power Factor

0.95 0.967

Ripple & noise

150mV 109mV

Set-up time

3000ms 1660ms

Rise time

80ms 23ms

Hold up time

50ms 56ms

Inrush current

65A 46.6A

Withstand voltage

I/P-O/P:3KVAC I/P-F/G:2KVAC O/P-F/G:0.5KVAC: TEST OK
Isolation resistance I/P-O/P, I/P-F/G, O/P-FG: 100mΩ/500VDC I/P-O/P: 22.4GΩ
I/P-F/G: 20.6GΩ
O/P-FG: 30FΩ
Brief Summary

After 10 years of use, the measured full load efficiency and power factor still within specification. 
This means the power components, such as MOSFETs and transformers were still working correctly.

Voltage ripple, set-up time and hld up time were also still within the specification.
This indicates that the lifetime of the capacitors at both the input and output sides were not over-aged.

Both the HI-pot and isolation still comply the relevant safety requirements, meaning the LED driver's isolation and moisture ingress protection remains intact, and it  is still able to withstand surges 

Analysis of Reliability Characteristics– Electrolytic Capacitor’s Capacitance 

Location

Specification

Actual Measurement Value

Input capacitor

C5 150µ/450V 105˚C

D=0.24

NCC CLA C:129.6µf D:0.08 ESR:0.574Ω
AUX power capacitor

C120

22µ/5V 105˚C D=0.1 NCC KY ESR=0.7Ω C:20.9µf D:0.06 ESR:0.43Ω

C55

100µ/25V 105˚C D=0.14 NCC KY ESR=0.22Ω C:89.4µf D:0.09 ESR:0.16Ω

C42

22µ/50V 105˚C D=0.19 RUB. YXM C:19.9µf D:0.08 ESR:2.2Ω

C52

47µ/35V 105˚C D=0.12 RUB. ZLH ESR=0.22Ω C:48.13µf D:0.06 ESR:0.183Ω
Output capacitor

C105

330µ/50V 105˚C D=0.1 NCC KY ESR=0.22Ω C:312µf D:0.025 ESR:0.037Ω

C106

330µ/50V 105˚C D=0.1 NCC KY ESR=0.22Ω C:313µf D:0.025 ESR:0.04Ω

C107

330µ/50V 105˚C D=0.1 NCC KY ESR=0.22Ω C:312µf D:0.025 ESR:0.04Ω

C109

120µ/63V 105˚C D=0.09 YXG-LLC ESR=0.25Ω C:111.7µf D:0.032 ESR:0.101Ω

Brief Summary

Capacitance, D (dissipation factor), and ESR (equivalent series resistance) all comply with the original component specifications. This means the design of the LED driver and the components selected meet MEAN WELL's long term reliability requirements.

Conclusion 

The priority for MEAN WELL when it comes to LED driver design and component selection is long-term reliability.  

By carrying out reliability testing (Limit of temperature ascent, ORT burn-in, thermal shock, vibration, salt spray…etc.), and the assessment of the electrical performance of the LED driver’s capacitors (isolation, lifetime…etc.) that have been in use for 10 years, MEAN WELL has demonstrated that both that their internal testing is reliable, and the quality of the LED driver is of a high standard.  

Adopting a high-efficiency design and choosing high-quality electrolytic capacitors ensure the reliability and lifetime of the LED driver.  

Selecting a trusted brand of LED driver is one of the simplest methods of upgrading the lifetime of LED lighting fixtures. 
 
MEAN WELL will continue with its policy of Total Quality Assurance & Customer Satisfaction to provide the best cost-performance LED drivers. 
 
For the lifetime evaluation and warranty statements, please contact ADM Systems on 1300 236 467

Mean Well logo

Authors: Sanford Su -  MEAN WELL Q.A. Dept & Aries Jian – MEAN WELL R&D Dept. 

Edited by: Stephen Lilley – ADM Systems Pty Ltd 

12 June 2019