Thermal management of through-hole leds

[Lauri Alanko]

I have some leds in 8 mm through-hole packages, rated for 0.5 W,
maximum steady current 100 mA. The legs are extra wide at the top, but
there is no other built-in heat sink. These are chinese cheapos from
ebay and no proper datasheet was supplied.

I intend to lay these out in a lattice on a stripboard, but I'm
worried about thermal issues. How closely can I position the leds? Do
copper strips provide enough additional heat dissipation area, or do I
need to etch and drill a PCB? At the very least I suspect I should
leave the legs sticking out from the board instead of cutting them.

Also, is there some way to measure the temperature of the led to check
if heat dissipation is sufficient?

Typical through-hole leds are low-power so heat isn't much of an
issue, and typical power leds are SMD and have dedicated heat sinks.
0.5 watt through-hole leds seem to be in a grey area and I can't find
much information on them. Any advice is appreciated.

Thanks,


Lauri

 

[George Herold]

On Tuesday, July 30, 2013 4:46:49 AM UTC-4, Lauri Alanko wrote:

I have some leds in 8 mm through-hole packages, rated for 0.5 W,

maximum steady current 100 mA. The legs are extra wide at the top, but

there is no other built-in heat sink. These are chinese cheapos from

ebay and no proper datasheet was supplied.



I intend to lay these out in a lattice on a stripboard, but I'm

worried about thermal issues. How closely can I position the leds? Do

copper strips provide enough additional heat dissipation area, or do I

need to etch and drill a PCB? At the very least I suspect I should

leave the legs sticking out from the board instead of cutting them.



Also, is there some way to measure the temperature of the led to check

if heat dissipation is sufficient?



Typical through-hole leds are low-power so heat isn't much of an

issue, and typical power leds are SMD and have dedicated heat sinks.

0.5 watt through-hole leds seem to be in a grey area and I can't find

much information on them. Any advice is appreciated.



Thanks,

I don't know about the 8mm leds. But for the 5mm ones if you look into the package you can see that the lead going to the anode (more positve end in normal operation) is mounted right to the device, whereas the cathode lead is a wire bound. (I don't know if this is universal or just the most common configuration). So I'm thinking that if you make a big copper pour for the anode side of the led that will help conduct some of the heat out of the led. Of course you still need to get rid of the heat in the copper on the pcb. To measure the temp you might try sticking a little thermocouple on the same anode leg.

George H.

Lauri

 

[John Larkin]

On Tue, 30 Jul 2013 08:46:49 +0000 (UTC), Lauri Alanko <la@iki.fi> wrote:

I have some leds in 8 mm through-hole packages, rated for 0.5 W,
maximum steady current 100 mA. The legs are extra wide at the top, but
there is no other built-in heat sink. These are chinese cheapos from
ebay and no proper datasheet was supplied.

I intend to lay these out in a lattice on a stripboard,

Hi, what do you mean by "stripboard?" Not those plug-in plastic breadboards, I
hope.


but I'm

worried about thermal issues. How closely can I position the leds? Do
copper strips provide enough additional heat dissipation area, or do I
need to etch and drill a PCB? At the very least I suspect I should
leave the legs sticking out from the board instead of cutting them.

The legs will help a little, but their surface area is small. Best thing would
be to solder the chip-side leg (as George says) to as much copper as possible,
as close to the LED as possible.

Air flow would help a lot, like a small fan.

Also, is there some way to measure the temperature of the led to check
if heat dissipation is sufficient?

A small thermocouple or thermistor glued to an LED in the middle of the array.
Wrap the lead wires around the LED a turn or two.

Typical through-hole leds are low-power so heat isn't much of an
issue, and typical power leds are SMD and have dedicated heat sinks.
0.5 watt through-hole leds seem to be in a grey area and I can't find
much information on them. Any advice is appreciated.

What are you making?


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[Michael Black]

On Tue, 30 Jul 2013, John Larkin wrote:

On Tue, 30 Jul 2013 08:46:49 +0000 (UTC), Lauri Alanko <la@iki.fi> wrote:

I have some leds in 8 mm through-hole packages, rated for 0.5 W,
maximum steady current 100 mA. The legs are extra wide at the top, but
there is no other built-in heat sink. These are chinese cheapos from
ebay and no proper datasheet was supplied.

I intend to lay these out in a lattice on a stripboard,

Hi, what do you mean by "stripboard?" Not those plug-in plastic breadboards, I
hope.


From the period reading electronic hobby magazines from the UK,

"stripboard" is perfboard with strips of foil along the holes along one
axis. So it's not perfboard with copper all over, but perfboard with
strips of copper. You cut where you don't need continuity.

Michael

but I'm
worried about thermal issues. How closely can I position the leds? Do
copper strips provide enough additional heat dissipation area, or do I
need to etch and drill a PCB? At the very least I suspect I should
leave the legs sticking out from the board instead of cutting them.

The legs will help a little, but their surface area is small. Best thing would
be to solder the chip-side leg (as George says) to as much copper as possible,
as close to the LED as possible.

Air flow would help a lot, like a small fan.


Also, is there some way to measure the temperature of the led to check
if heat dissipation is sufficient?

A small thermocouple or thermistor glued to an LED in the middle of the array.
Wrap the lead wires around the LED a turn or two.


Typical through-hole leds are low-power so heat isn't much of an
issue, and typical power leds are SMD and have dedicated heat sinks.
0.5 watt through-hole leds seem to be in a grey area and I can't find
much information on them. Any advice is appreciated.

What are you making?


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[Ian Field]

"George Herold" <gherold@teachspin.com> wrote in message
news:f28174e7-0e98-4f00-b89b-dfae4fdf4071@googlegroups.com...

On Tuesday, July 30, 2013 4:46:49 AM UTC-4, Lauri Alanko wrote:
I have some leds in 8 mm through-hole packages, rated for 0.5 W,

maximum steady current 100 mA. The legs are extra wide at the top, but

there is no other built-in heat sink. These are chinese cheapos from

ebay and no proper datasheet was supplied.



I intend to lay these out in a lattice on a stripboard, but I'm

worried about thermal issues. How closely can I position the leds? Do

copper strips provide enough additional heat dissipation area, or do I

need to etch and drill a PCB? At the very least I suspect I should

leave the legs sticking out from the board instead of cutting them.



Also, is there some way to measure the temperature of the led to check

if heat dissipation is sufficient?



Typical through-hole leds are low-power so heat isn't much of an

issue, and typical power leds are SMD and have dedicated heat sinks.

0.5 watt through-hole leds seem to be in a grey area and I can't find

much information on them. Any advice is appreciated.



Thanks,

I don't know about the 8mm leds. But for the 5mm ones if you look into
the package you can see that the lead going to the anode (more positve end
in normal operation) is mounted right to the device, whereas the cathode
lead is a wire bound. (I don't know if this is universal or just the most
common configuration).

It used to be a reliable indication that the cathode was always the
"pedestal" lead frame, but around the 80's or 90's they came up with a new
material for ultra-bright LEDs with the "pedestal" lead frame was the anode.

So I'm thinking that if you make a big copper pour for the anode side of
the led that will help conduct some of the heat out of the led. Of course
you still need to get rid of the heat in the copper on the pcb. To
measure the temp you might try sticking a little thermocouple on the same
anode leg.

A good idea in principle - but melting loads of solder on carries the risk
of cooking the LED before current flow gets anywhere near it.

Low melting point solder maybe, but the last time I saw any it was cadmium
based - probably banned by RoHS.