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Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.
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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?

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On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?


The only holes are mechanical fixing holes, none go through the
copper.

To complete the prototype I'm removing the insulation layer around a
couple of holes to give bare aluminium on the top and creating an ac
ground with capacitors from 0V and +50V to solder tags secured by the
mounting srews.
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Raveninghorde wrote:

Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb


Is that on one side ?


is not earthed causing problems with current control


What sort of problems ? Decouple every few LEDs to GND if it's HF ?


presumably due to much higher stray capacitance than we had on FR4.
Just got to find a neat way of earthing it.


So what material is that if not FR4 ?

Graham

p.s. 19k lumens ! What's it a replacement for ?


--
due to the hugely increased level of spam please make the obvious
adjustment to my email address


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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".


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On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?



I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.
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On Thu, 25 Jun 2009 23:50:51 +0100, Eeyore
wrote:

So what material is that if not FR4 ?

Graham


G10 perhaps. There are others available as well.
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On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL
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On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL



SMT LEDs are SMT capable (duh). That means a 500 F heat bath (or more
for RoHS). It can handle it, and likely more than one cycle.

The preheat remains the same. It is not like he used an 0.090" thick
PCB.
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On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


That is aluminum clad? There are holes through it? Are they isolated?



I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


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On Thu, 25 Jun 2009 23:50:51 +0100, Eeyore
wrote:



Raveninghorde wrote:

Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb


Is that on one side ?


is not earthed causing problems with current control


What sort of problems ? Decouple every few LEDs to GND if it's HF ?


presumably due to much higher stray capacitance than we had on FR4.
Just got to find a neat way of earthing it.


So what material is that if not FR4 ?


http://www.aismalibar.com/archivos/8...pdf?download=1



Graham

p.s. 19k lumens ! What's it a replacement for ?


A light bulb Out door space lighting.
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On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.
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On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL


The S pattern is just to keep the orientation the same for all the
leds.

The copper free areas are due to the design of the reflector which
bolts down on the board.
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On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


To follow up on that. The colour temperature is dependant on LED
current so the current needs to be correct. Dimming is done by PWM so
that the on current doesn't change.

The LED voltage is specified as 2.7V to 3.8V at room temperature with
0.4V change over the temperature range. The LED voltage variation is
bad because the LEDs are matched for brightness and colour
temperature.

Based on the above the current has to be actively controlled. In this
case using a Supertex IC.
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On Fri, 26 Jun 2009 09:46:01 +0100, Raveninghorde raveninghorde@invalid
wrote:

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.



For LEDs? Whatever happened to the tried and true series resistor?


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On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde raveninghorde@invalid
wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


NOT EACH LED.
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On Fri, 26 Jun 2009 13:04:23 +0100, Raveninghorde raveninghorde@invalid
wrote:

On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


To follow up on that. The colour temperature is dependant on LED
current so the current needs to be correct. Dimming is done by PWM so
that the on current doesn't change.


How do you insure that the same voltage is found anywhere along the
physical rail?

The LED voltage is specified as 2.7V to 3.8V at room temperature with
0.4V change over the temperature range. The LED voltage variation is
bad because the LEDs are matched for brightness and colour
temperature.

OK, so you match and cull.

Based on the above the current has to be actively controlled. In this
case using a Supertex IC.


The series resistor is for max current limiting.
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On Fri, 26 Jun 2009 09:56:13 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL


The S pattern is just to keep the orientation the same for all the
leds.

A 90 degree rotation would afford the same feature, without involving
the dissipating areas.

The copper free areas are due to the design of the reflector which
bolts down on the board.


reflector? not a diffusor?

Good luck in reflow.

RL
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On Thu, 25 Jun 2009 19:39:35 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL



SMT LEDs are SMT capable (duh). That means a 500 F heat bath (or more
for RoHS). It can handle it, and likely more than one cycle.

The preheat remains the same. It is not like he used an 0.090" thick
PCB.


Try it some time.

RL
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On Fri, 26 Jun 2009 20:12:27 -0400, legg wrote:

On Thu, 25 Jun 2009 19:39:35 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL



SMT LEDs are SMT capable (duh). That means a 500 F heat bath (or more
for RoHS). It can handle it, and likely more than one cycle.

The preheat remains the same. It is not like he used an 0.090" thick
PCB.


Try it some time.

RL


THINK, idiot. If it is made by an SMT device vendor, and it is claimed
to be an SMT part, then it can handle an SMT reflow oven thermal cycle.
If it cannot, it is NOT an SMT part.

If it is an RoHS SMT part, it has an even higher temperature handling
capacity.

Only idiots that attempt to spirit their assemblies through the reflow
oven too quickly have problems with thermal profiles.


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On Fri, 26 Jun 2009 20:10:27 -0400, legg wrote:

On Fri, 26 Jun 2009 09:56:13 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL


The S pattern is just to keep the orientation the same for all the
leds.

A 90 degree rotation would afford the same feature, without involving
the dissipating areas.

The copper free areas are due to the design of the reflector which
bolts down on the board.


reflector? not a diffusor?

Good luck in reflow.

RL


Our reflow is not up to this job and will be replaced if this goes
into production. I'll replace it anyway as soon as I get sight of the
right second hand machine.

I had the boards assembled by the company who made the blank pcbs.
They specialise in this stuff. They did a great job, 48 hours from
gerbers to assembled boards.

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On Sat, 27 Jun 2009 10:08:29 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Fri, 26 Jun 2009 20:10:27 -0400, legg wrote:

On Fri, 26 Jun 2009 09:56:13 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 22:28:13 -0400, legg wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

Why the 'S' pattern, and why copper-free areas (if thermals are an
issue)?

Must be a really hefty pre-heat for reflow. Are the leds compatible to
this fab step, at all?

RL

The S pattern is just to keep the orientation the same for all the
leds.

A 90 degree rotation would afford the same feature, without involving
the dissipating areas.

The copper free areas are due to the design of the reflector which
bolts down on the board.


reflector? not a diffusor?

Good luck in reflow.

RL


Our reflow is not up to this job and will be replaced if this goes
into production. I'll replace it anyway as soon as I get sight of the
right second hand machine.

I had the boards assembled by the company who made the blank pcbs.
They specialise in this stuff. They did a great job, 48 hours from
gerbers to assembled boards.


It's not often true, that what you don't see, can't hurt you. I
suggest that you inquire as to the equipment and techniques that were
used successfully.

RL
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On Fri, 26 Jun 2009 09:46:01 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

That is aluminum clad? There are holes through it? Are they isolated?



I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


It's hard to imagine that the pcb adds much capacitance. You could
measure it.

Maybe the instability comes from a shared-ground problem.

John

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On Fri, 03 Jul 2009 15:11:10 -0700, John Larkin
wrote:

On Fri, 26 Jun 2009 09:46:01 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

That is aluminum clad? There are holes through it? Are they isolated?


I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


It's hard to imagine that the pcb adds much capacitance. You could
measure it.

Maybe the instability comes from a shared-ground problem.

John



Surface mount solder stripped and tinned segments of 16 Ga. SPC wire
along the trace runs between devices. Much better than mere clad media
alone.

I would have designed it that way. Bare 'pads' right on the traces
that allow one to add wire segments as those I described. It turns any 4
oz pwa into a proper, point-to-point wired device. That makes the pwa
just a backbone for the conductors, as it should be. It already is, but
it would also definitely be better with the added wires. Every milliohm
counts.
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On Fri, 03 Jul 2009 15:11:10 -0700, John Larkin
wrote:

On Fri, 26 Jun 2009 09:46:01 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

That is aluminum clad? There are holes through it? Are they isolated?


I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


It's hard to imagine that the pcb adds much capacitance. You could
measure it.

Maybe the instability comes from a shared-ground problem.

John


The prototype was on standard FR4 and worked fine. We had to add an RC
damping circuit to get it stable on the Cobritherm board. I've got 2
led strings and controllers on each board and noticed that the two
channels syncronised to the same frequency. This definitely didn't
happen on FR4.

I'll measure the capacitance to see if it was the problem.

As to shared ground I'm sure that that wasn't the problem, which
probably means it is. The first rule of fault finding is that the
fault is where you are not looking for it.


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On Fri, 03 Jul 2009 15:11:10 -0700, John Larkin
wrote:

On Fri, 26 Jun 2009 09:46:01 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:22:21 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 07:11:19 -0400, Spehro Pefhany
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde
raveninghorde@invalid wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.

That is aluminum clad? There are holes through it? Are they isolated?


I think he is nuts. Looks like copper to me. What PCB houses use Al
clad media? What etching process works with AL cladding?

What solder sticks to Al cladding.

Current control should be easy and precise, even with ALL of them
floating without "earth" grounding.



The pcb is an aluminium plate with a very thin insulator and a copper
layer.

http://www.aismalibar.com/archivos/8...pdf?download=1

Current control was stable on FR4 prototype but the higher capacitance
is causing interaction between current controllers.


It's hard to imagine that the pcb adds much capacitance. You could
measure it.

Maybe the instability comes from a shared-ground problem.

John


Apparently the dielectric between the copper cladding layer and the
aluminium core is only 12um in this product. I think from previous
work that this can raise capacitance into the 400pF/cm^2 range. I had
thought from the previous description that he was using an al-cored
stack-up (fr4 layer insulation).

I don't know what control or modulation method is being used, so I
can't comment on sources of chaotic behaviour. I hope he's substituted
a known-good control section at some point, before beginning to
suspect the new layout.

Previous comments re thermals on copper-clad Al are amplified
three-fold with this particular material. It takes a lot of energy to
make an Al plate follow the recommended thermal profile of the opto
expected standard reflow. Dwell times are particularly difficult to
terminate.

RL
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On Sat, 04 Jul 2009 02:40:01 -0400, legg wrote:


Apparently the dielectric between the copper cladding layer and the
aluminium core is only 12um in this product. I think from previous
work that this can raise capacitance into the 400pF/cm^2 range. I had
thought from the previous description that he was using an al-cored
stack-up (fr4 layer insulation).


That should have been 120um.

RL
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Raveninghorde wrote:

Eeyore wrote:
Raveninghorde wrote:

Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb


Is that on one side ?

is not earthed causing problems with current control


What sort of problems ? Decouple every few LEDs to GND if it's HF ?

presumably due to much higher stray capacitance than we had on FR4.
Just got to find a neat way of earthing it.


So what material is that if not FR4 ?


http://www.aismalibar.com/archivos/8...pdf?download=1


Ah thanks, that might come in useful for a project a colleague and I have in mind.


p.s. 19k lumens ! What's it a replacement for ?


A light bulb Out door space lighting.


What's the current luminaire ?

Graham


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Raveninghorde wrote:

Capt. Cave Man wrote:

Current limit resistors ARE the cheapest, most efficient "current
control".


No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


A while back I developed a low minimum Vf ( about 0.5V ? possibly less )
constant current source using a switching circuit and ultra low Vcesat Zetex
devices. There were only good for about 1-2A IIRC though.

It simulated OK but not built yet.

I imagine Cap'n Cave Man must be DimBulb a.k.a AlwaysWrong.

Graham


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On Sat, 11 Jul 2009 15:37:04 +0100, Eeyore
wrote:

I imagine Cap'n Cave Man must be DimBulb a.k.a AlwaysWrong.

Graham



We were talking about LEDs. Don't limit the current, and you get a
fried LED.


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life imitates life wrote:

On Sat, 11 Jul 2009 15:37:04 +0100, Eeyore
wrote:

I imagine Cap'n Cave Man must be DimBulb a.k.a AlwaysWrong.

Graham


We were talking about LEDs. Don't limit the current, and you get a
fried LED.


Where did I suggest not limiting the current ? I suggested a switching
constant current source with very low dissipation and wide input voltage
tolerance.

READ what people write.

Graham


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On Wed, 15 Jul 2009 00:45:25 +0100, Eeyore
wrote:



life imitates life wrote:

On Sat, 11 Jul 2009 15:37:04 +0100, Eeyore
wrote:

I imagine Cap'n Cave Man must be DimBulb a.k.a AlwaysWrong.

Graham


We were talking about LEDs. Don't limit the current, and you get a
fried LED.


Where did I suggest not limiting the current ? I suggested a switching
constant current source with very low dissipation and wide input voltage
tolerance.

READ what people write.

Graham



I read what you wrote. Yeah, you know, the jack-jawed comment about
imagining something.

I imagine that you are wrong more often than I ever could be.
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On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.



Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


You must be thinking of HPS luminaries and lamps. See ANSI standard
lamp codes S55 and S66.
LED power input for 19,000 lumens should be 30 watts or less.
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On Fri, 26 Jun 2009 13:04:23 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


To follow up on that. The colour temperature is dependant on LED
current so the current needs to be correct. Dimming is done by PWM so
that the on current doesn't change.


I has the understanding that the current dependency is stronger. Of
course both increased current lambda shift and increased thermal
lambda shifts are in the same direction.

The LED voltage is specified as 2.7V to 3.8V at room temperature with
0.4V change over the temperature range. The LED voltage variation is
bad because the LEDs are matched for brightness and colour
temperature.


And spot matched at that. Moreover you have not told us whether or
not you are mixing in phosphor type "white" LEDs in your luminaire.

Based on the above the current has to be actively controlled. In this
case using a Supertex IC.

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On Thu, 16 Jul 2009 20:08:49 -0700,
wrote:

On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".



No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


You must be thinking of HPS luminaries and lamps. See ANSI standard
lamp codes S55 and S66.
LED power input for 19,000 lumens should be 30 watts or less.


How do you get 30 watts?

The leds are Osram LUW W5AM-LXLY-6P7R.

I have 168 112 lumen leds driven at 350mA with a forward voltage of
about 3.2V +/- 0.5V. That gives me 188 watts for 18800 lumens.


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On Fri, 17 Jul 2009 11:02:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 16 Jul 2009 20:08:49 -0700,
wrote:

On Fri, 26 Jun 2009 09:52:54 +0100, Raveninghorde
raveninghorde@invalid wrote:

On Thu, 25 Jun 2009 17:20:18 -0700, Capt. Cave Man
wrote:

On Thu, 25 Jun 2009 11:40:39 +0100, Raveninghorde raveninghorde@invalid
wrote:


Here is my new light bulb, minus reflector.

168 112 lumen leds in 14 strings.

The main problem is the aluminium of the pcb is not earthed causing
problems with current control presumably due to much higher stray
capacitance than we had on FR4. Just got to find a neat way of
earthing it.


Is there not a current limit resistor at each LED?

Capacitance has an effect? Improper design then.

Current limit resistors ARE the cheapest, most efficient "current
control".


No. Resistors are not efficient they dissipate and take board space,
they are not even particularly cheap at these power levels. The leds
take about 180 Watts.


You must be thinking of HPS luminaries and lamps. See ANSI standard
lamp codes S55 and S66.
LED power input for 19,000 lumens should be 30 watts or less.


How do you get 30 watts?

The leds are Osram LUW W5AM-LXLY-6P7R.

I have 168 112 lumen leds driven at 350mA with a forward voltage of
about 3.2V +/- 0.5V. That gives me 188 watts for 18800 lumens.


Much of the literature that i have seen gives about 1/6 the power
using LEDs instead of incandescent. Oops. I did not compare apples
to apples. I knew LEDs were beating all but the exotic variations on
incandescent for lm/W. Had not realized that they were merely on par
with HPS. LEDs still win on life, having better graceful degradation
modes, on-off properties and dimmability.
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