Another phase of this road test deals with power LEDs. I wanted to publish something to show progress in this area and I finally have enough parts to build an initial demonstration.
This blog covers preliminary connection of the TI TPS92512EVM-001TPS92512EVM-001 to some power LEDs to get a feel for how much heat is generated. Making the box for the module took some time, but is not the focus of this phase.
Here are some of the calculations and data I am messing around with to figure out heatsinks and drive currents:
6 LEDs nominally able to handle 3 Watts each with appropriate heat sinks.
Driver efficiency = 90%
LED efficiency = 25%
Input power = 12 V x 1.4 A = 16.8 W
Power to LEDs = .9 x 16.8 = 15.12 W
Power to each LED = 15.12 / 6 = 2.52 W
Power as light from each LED = 2.52 x .25 = .63 W
Power as heat from each LED = 2.52 x .75 = 1.89 W
Total heat to dissipate from 6 LEDs = 11.34 W
Max junction temperature = 130 C (for long life)
Max heatsink temp = 55 C (to avoid burning skin)
Here is a flat plate heat sink chart I found on the internet - I am not sure how good it is yet:
It indicates I need 100 sq cm, however in my test this still got too warm, so I need to increase the heatsink area.
I increased the heatsink area from 101 square cm to 250 sq cm and it eliminated overheating. The temperature now stays below 46 C. The aluminum I am using is too thin to work optimally - the edges are 10 degrees cooler than the middle. If the material was thicker it would conduct more heat to the edges and they would play a larger role in dissipating the heat. Here is a picture of the beefed up heatsink:
Here is another little application idea for white LEDs that I completed some time ago:
The ring light is mostly used for macro photography, but I often use it for other indoor video work.
The ring of LEDs is a commercial "angel eyes" circuit card normally used for headlights, so it runs off 12-15 volts. It has 33 LEDs. The ring I used has an inner diameter of 83.8 mm and an outer diameter of 100 mm. It is powered from a custom module I designed that converts 5 V to 12-15 V, so I can use a standard USB power supply to run it. The 3D printed ring diffuser and quick-connect tripod mount allow access to my camera battery and memory card.
I have an extra ring and it just occurred to me how it can be easily modified to run of the TI power LED driver, simply short all resistors. Here is what it looks like, although I am running at low current to avoid over saturating the camera.
Incidentally the Würth LEDs look like they would fit on this ring PCB, however I'm not sure it would provide adequate heatsinking as they are much brighter LEDs.
What you can do with the Würth LEDs is connect them on aluminum circuit cards intended for other form factor LEDs.
Here is what that looks like - I have soldered twice as many LEDs as the card was intended to carry, one on each lead - using the central heatsink pad to connect each pair. I was worried that all central pads were common, which would prevent this from working, but it turns out they are all isolated from each other. You will need a fairly high power soldering iron as the aluminum card is hard to heat up. It is also tricky to get some heatsink compound under each LED and get them to lie flat for good contact. But it is possible as shown here:
Here is what they look like turned on - again at low current to allow the camera to capture a reasonable picture:
The LED Road Test page is here:
http://www.element14.com/community/roadTests/1481
The Lighting Group page is here:
Here are links to my other blog entries for this road test:
LED Road Test - Proposal - Blog 0 Jan 1, 2016
Light Emitting Diodes Road Test - Blog 1 Nov 1
LED Road Test - 3D Printed Housings - blog 2 Nov 10
LED Road Test - Dodecahedron Light Fixture Blog 3 Nov12
LED Road Test - Wearable Interactive Lights - Blog 4 - Nov 13
LED Road Test - Interactive Trophy - Blog 5 Nov 16
LED Road Test - Making Household Objects Interactive - Blog 6 Nov 22
LED Road Test - Power LEDs - Up & Running - Blog 7 Nov 24
LED Road Test - Star Wars - The Force Awakens - Blog 8 Nov 28
LED Road Test - Selfie Phenomenon - Blog 9 Nov 29
LED Road Test - MSP EXP430FR4133 Launchpad IDE - Blog 10 Dec 6
LED Road Test - Vehicle Situational Awareness System Blog 11 Dec 14
LED Road Test - Vehicle Situational Awareness System Indoor Demo - Blog 12 Dec 20
LED Road Test - Maple Leaf Christmas Decoration - Blog 13 Dec 24
LED Road Test - Reflow Soldering Power LEDs - Blog 15 Jan 10
LED Road Test - Induction Heating Reflow Soldering - Blog 16 Jan12
LED Road Test - Summary - Blog 17 Jan 15
Associated Video Links
Creating a Light Fixture using 123D Design
Wearable Interactive Arc Reactor
Interactive Illuminated Household Objects
Star Wars - Let The Force Be With The Light
Vehicle Situational Awareness System in Operation
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