LED Thermal Management

27 October, 2017

Designing LED products in a rapidly growing and highly competitive market is a daunting task. Tom Gregory, 6SigmaET Product Manager, explains how thermal simulation software can support lighting design engineers

According to some estimates, lighting constitutes around one sixth of total worldwide electricity consumption – and that figure is considerably higher in industrialised nations. That represents significant power consumption – so it’s no surprise that more energy efficient lighting has been a focus for several years.

That’s seen the rise to prominence of LED lighting. Not only does it deliver more brightness per watt of electricity consumed, reducing overall energy consumption in use, but also its longer lifetime means reduced energy consumption in manufacturing.

LED lighting requires a new generation of power electronics – drivers and power supplies, of which there is a broad range commensurate with the broad range of applications in which LED lighting is being deployed. ‘Efficiency’ is the key word: an LED driver that is 95% efficient will consume substantially less power during its extended lifetime than a driver that is, say, 80% efficient.

Even if the driver is highly efficient, LED lighting designers must still contend with the issue that, of the energy supplied, only around 35% is converted into usable light: the remaining 65% is lost to heat. 

The Life of an LED

And therein lies a problem. The life of an LED – like any electronic device – depends on it being cooled appropriately. In many cases, that leads designers to review the broad range of alternative heat dissipation modes available – conduction, convection and radiation. Adhesive is often used to bond the LED with the board, and the use of thermally conductive materials can be advantageous. The size, shape, design, construction material, finish and mounting method of heatsinks will potentially be an important choice.  A Metal Core Printed Circuit Board (MCPCB) which incorporates a base metal material as a heat spreader as an integral part of the circuit board, and which can take advantage of incorporating a dielectric polymer layer with high thermal conductivity for lower thermal resistance, may well be considered.

In some applications, more active cooling paradigms – such as fans – may be an alternative: providing additional airflow can provide additional heat dissipation of up to 40%, but the noise, weight, space and reliability characteristics of fans often preclude their use. More esoteric options such as heat pipes and vapour chambers may also be an option.

The problem is exacerbated to a considerable extent by the fact that, while more traditional lighting solutions have a maximum junction temperature of around 2,000°C, that of an LED needs to be closer to 100°C if it is to achieve its desired lifetime. That’s some design challenge.

There are, inevitably, trade-offs in making those product selections and design decisions. Not least amongst these is expense, if cost goals in a competitive market are to be met. A ‘better’ heat transfer solution, for example, is likely to be more expensive than one that appears not so well-suited but is its additional capability necessary?

Banking on Thermal Simulation Analysis

Only so much help can be given to the design process by analytical calculation and experimental measurements; it is only feasible to produce a limited number of prototypes. Simulation of the results of different design approaches becomes necessary at some point – and that’s what 6SigmaET thermal simulation software was designed for.

It has been used for simulating, for example, different configurations of printed circuit board (PCB) in the design of an LED downlighter – and demonstrating that temperature drop across a specific type of PCB would be sufficiently severe to disqualify the use of a natural convection heat sink. An optimised MCPCB was simulated, an appropriate heat sink size determined using analytical methods – and performance confirmed using 6SigmaET.

6SigmaET is a computational fluid dynamics (CFD) simulation tool that can bring new levels of productivity to LED cooling design. Thanks to its ease-of-use, it overcomes many of the deficiencies of other tools available in the market. With substantial automation and intelligence – the latest Release 11 of the software, for example, now provides a novel way to remove the burden of having to manually optimise the grid by navigating the trade-off between computing performance and grid detail to provide optimum accuracy and performance – 6SigmaET is already being used by a global community of design engineers.

A recent market report by Edison forecast that the total lighting market will be worth €100 billion by 2020. In the ten years until then, LED will have increased its share from 12% to 63%. With that kind of value and growth, the LED lighting industry will only become more competitive – and the winning companies will be those leveraging the advanced tools available to reduce design risk, reduce time to market and maximise competitive advantage. 

By: Tom Gregory, Product Manager