The Lifespan of a PSU

PSU Lifespan

Introduction

An important question that often arises within the power electronics industry relates to the lifespan of a power supply unit. What is the usual lifespan for a PSU and what dictates its life expectancy? In this article, we examine the key factors that determine how long a power supply will last.

Power Supply Life Expectancy

 The lifespan of a power supply is typically shorter than other small signal electronic circuits due to the heat that is generated by the power supply unit. Heat accelerates and acts as a catalyst for aging key components situated within the power supply.

 

E-caps

The lifetime of a typical external AC/DC power supply is determined by the Electrolytic capacitors (E-caps). Whilst other components e.g. opto-couplers can also deteriorate over time they seldom dictate the product life to the same level as the E-caps.

E-caps wear-out over time as their electrolyte dries out. There are a number of ratios and coefficients which contribute to the wear-out mechanism calculation for a given capacitor but these are dominated by the operating temperature, ripple current and ESR (equivalent series resistance).

 

5-10 years Becoming the Norm

The typical lifetime expectation for a CPE power supply is between 5 or 10 years and many operators require that power supplies are designed to follow the IPC9592B standard which sets out two performance levels:

  • Class I – 5 years life with 40C ambient, 80% of rated load – applies to general or standard, e.g. consumer Telco applications.
  • Class II – 10 years life with 40C ambient, 80% of rated load – applies to enhanced or dedicated service e.g. carrier grade Telco applications.

Whilst the lifetime expectations mentioned above greatly exceed the PSU and CPE warranty period, operators commonly still prefer to ensure that their products are capable of remaining operational long after initial deployment, thereby ensuring customer satisfaction/retention and avoiding service call costs.

 

Design Considerations

To ensure that a power supply design is compliant with the lifetime expectations it’s essential to consider the following:

  • Efficiency – optimise the power conversion efficiency of the power supply – the dissipated power density (wasted heat in a given volume) will have a very high influence on the ambient temperatures seen by the E-caps. Power dissipated in the DC cable whilst important for compliance with energy efficiency legislation will have little effect on the lifetime.

 

  • Size – Ensure that the physical size/industrial design of the product is appropriate for the level of power provided and that the correct choice is made between wall-mount and desktop formats. Refer to ‘Desktop vs Wall-Mount’ white paper

 

  • Component layout – Avoid internal “hot-spots” e.g. Transformer windings, heatsinks, resistor fuse and ensure sufficient spacing or thermal isolation of E-caps from adjacent components which are heat generators.

 

  • Current and Voltage Rating – Carefully define the rated current and operating voltage range for the power supply as well as the test conditions to be used for the lifetime calculation following industry standards (e.g. IPC9592)

 

  • Test Conditions – Use nominal or nameplate AC input voltage as opposed to worst case operational to avoid over-specifiying the design which can drive up cost and/or size increases to cover a scenario which doesn’t accurately consider the life-time of the product in the real-life application.

 

  • E-Cap Selection – Pay particular consideration to the choice of E-cap vendor! Process capabilities vary hugely throughout the industry and its vitally important to have a robust methodology in place for E-cap vendor selection including ongoing reliability programs and guarantees.

 

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Conclusion

The PSU lifespan is decided by a number of critical factors. When carefully considered during the requirement definition of a new design, the lifetime of the PSU can be optimized to ensure trouble free service for both operators and consumers in a cost-effective manner.

To find out more about NetBit’s PSU products click here.