Thermal ManagementMaster-class

Dr Andy E Youngandrew.young@litecool.co.uk

Overview

• Why is thermal design so important?• What are the challenges and solutions?• What factors effect..– Performance?– Reliability?– Cost?

• Where are the common mistakes made?

Let’s start with some questions for you..

Question to the audience

When you design a luminaire do you..A. Set the current and live with the lumens?B. Drive the LED harder and live with consequences?

Where is your ‘weakest link’ in thermal performance?C. PackageD. ModuleE. Luminaire body

Are you confident your thermal performanceis as good as it could be?

Why is thermal performance so important?..

Why is thermal design so important?

• Electrical current generateslight and heat

• Cooler means morelight is generated

• Maximum light needs both–High current– Low

• This is a vicious-circle!

Future Light Solutions, ULT2.0 tutorial

What are the challenges?..

What are the challenges?

• High current and low appear to be mutually exclusive

• Complicated interactions• The data provided is

incomplete, and• Where available it is

often for lab conditionseg.

What are the solutions?..

What are the solutions?• Brute force– Over-engineered heat-sinks, etc.– Build-in active technology eg. fans

• Apply thermal management technology– Close the loop in performance evaluation– Address root causes– For real-world conditions

• Good thermal design can..Build in the right technology, in the right place

convert a vicious-circle into a virtuous-circle!

What factors affect performance?..

What factors affect performance?• Goal: find design for and• is dependent on and• Denotes from LED package datasheet• Denotes from luminaire type• Denotes from thermal design

How to determine these values?

Missing value!

What factors affect performance?Missing data

• Related to the thermodynamic efficiency of the LED, referred to as the wall-plug efficiency

• Hard to find, Often guessed at eg. 80%• Can be..

Measured, or Calculated

Photopicsensitivity

Normalised Plank function

• The numbersscale thesignificanceof the variousthermal resistances

What factors affect performance?Luminaire type

Digital Lumens

0 200 400 600 800 1000 1200 1400 1600 1800 20000

0.5

1

1.5

2

2.5

What factors affect performance?From thermal design

• Conventional wisdom tells us thin layers are less resistive

• All thermal resistances are composed of two effects..

Substrate0

0.5

1

1.5

2

2.5

Exploiting the virtuous circle• Same ..

• Lower and• Achieved by thermal design of package and module

What factors affect reliability?

• Indicated by • Strongly dependent on

and

What factors effect.. Cost

• Luminaire cost– Good thermal design can reduce cost if done well– $8 on down-light– $30 on a high-bay

• Life cost– Indicated by E and L70– Strongly dependent on Tj

Common errors

1. Taking data on face value2. Thinking in 1D3. Component-by-component design4. Neglecting interfaces5. Not using TIM well6. Thermal tolerance stack-up7. Assuming it is all about the heat-sink8. Treating a luminaire body as a heat capacitor9. And then adding long fins10. Giving me less than a 5 on the feedback

Thank you from

Thermally efficientLED Modules

andrew.young@litecool.co.uk