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Clive Arthur
Guest

Fri Jan 06, 2017 5:59 am   



On 05/01/2017 19:20, Winfield Hill wrote:
Quote:
Clive Arthur wrote...

I want to run a microcontroller circuit at about 3V 10mA
on the high side of a several kilovolt supply. I know
there are various solutions, but I'd like to use a
'solar cell' to supply isolated power.

A home-made transformer is completely practical.
I made a 0 to 250V supply, floating on top of 15kV,
using a simple TL494 driving a 1:1:10 transformer
at 50kHz. I used a 0.47-inch dia core and machined
a special two-section bobbin, with 1-inch inner dia,
giving 0.25-in insulation. The two sections were
separated by 0.20 in, overall bobbin length 0.8 in.
This performed flawlessly. (The feedback scheme I
chose for the supply was a bit dicey, requiring two
30kV 150M resistors, with considerable care for the
mounting and insulating.) Reference RIS-623.


Thanks, Win, but Tim is right, it should be fun and a bit different.

I've used packaged photovoltaic isolators before for micropower things -
a few uA at a few V is quite usable and of course it's DC-DC with no
switching so really simple to do.

In the present case, I rather think the customer would like the
reassurance of a visible air gap, and if achievable, a low efficiency of
1% is simply not an issue.

Cheers
--
Clive

Phil Hobbs
Guest

Fri Jan 06, 2017 6:26 am   



On 01/05/2017 04:59 PM, Lasse Langwadt Christensen wrote:
Quote:
Den torsdag den 5. januar 2017 kl. 22.42.58 UTC+1 skrev John Larkin:
On Thu, 5 Jan 2017 14:46:04 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/05/2017 01:53 PM, John Larkin wrote:
On Thu, 5 Jan 2017 10:24:01 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Thursday, January 5, 2017 at 12:42:48 PM UTC-5, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some orders of
magnitude, so I'm considering using one or more photovoltaic cells with
one or more LEDs shining on them. It's all in an enclosure, so there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW? I guess blue LEDs
would be best? An efficiency of 1% (a 3W input) would be fine, even a
bit less. Just musing at the moment and if anyone has any ball-park
feelings or experience that would be good.

Cheers
--
Clive

There are high isolation DC-DC converters out there, not cheap, but ultimately superior to a photvoltaic system.
http://www.mouser.com/search/Refine.aspx?Keyword=164194258&Ns=Pricing%7c0&FS=True&Ntk=P_MarCom

A home-made inductive coupling thing wouldn't be difficult. It could
work through a piece of plexiglas for visible isolation, or just be
traces on opposite sides of a PC board. That could be really cheap in
production.

Or wind a ferrite toroid to make a transformer, and use really well
insulated wire.

But as you say, it's a lot easier to buy an appropriate dc/dc
converter.

For uA of current using a stack of photodiode optocouplers could work,
but for mA inductive coupling is likely the way to go.

The Starbucks near me has those "Powermat" chargers where you stick an
inductor ring to your phone's charging port and lay it on the inductor
ring on the table; I guess they chop the AC up to a high enough freq
that air makes a decent enough core, and a loop only slightly larger
than a quarter can transfer enough energy to charge up a smartphone in
under an hour

Let's spread the rumor that the field will cause warts or insanity or
something.


the promise of wireless power seems to be able to cause some forms of insanity

https://ubeam.com/technology/

https://youtu.be/ukgnU2aXM2c?t=14m21s


And in general:

http://liesandstartuppr.blogspot.com

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

bitrex
Guest

Fri Jan 06, 2017 8:30 am   



On 01/05/2017 08:53 PM, krw_at_notreal.com wrote:
Quote:
On Thu, 5 Jan 2017 14:46:04 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/05/2017 01:53 PM, John Larkin wrote:
On Thu, 5 Jan 2017 10:24:01 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Thursday, January 5, 2017 at 12:42:48 PM UTC-5, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some orders of
magnitude, so I'm considering using one or more photovoltaic cells with
one or more LEDs shining on them. It's all in an enclosure, so there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW? I guess blue LEDs
would be best? An efficiency of 1% (a 3W input) would be fine, even a
bit less. Just musing at the moment and if anyone has any ball-park
feelings or experience that would be good.

Cheers
--
Clive

There are high isolation DC-DC converters out there, not cheap, but ultimately superior to a photvoltaic system.
http://www.mouser.com/search/Refine.aspx?Keyword=164194258&Ns=Pricing%7c0&FS=True&Ntk=P_MarCom

A home-made inductive coupling thing wouldn't be difficult. It could
work through a piece of plexiglas for visible isolation, or just be
traces on opposite sides of a PC board. That could be really cheap in
production.

Or wind a ferrite toroid to make a transformer, and use really well
insulated wire.

But as you say, it's a lot easier to buy an appropriate dc/dc
converter.

For uA of current using a stack of photodiode optocouplers could work,
but for mA inductive coupling is likely the way to go.

The Starbucks near me has those "Powermat" chargers where you stick an
inductor ring to your phone's charging port and lay it on the inductor
ring on the table; I guess they chop the AC up to a high enough freq
that air makes a decent enough core, and a loop only slightly larger
than a quarter can transfer enough energy to charge up a smartphone in
under an hour

My last couple of phones have had this built in. It's know as Xi
(pronounced "chee"). I "hang up" my cell phone on one when I get
home.


If you're the type of plug-in hybrid driver who finds it just too
burdensome to plug in a cable, you can even have one for your car. ;-)

https://www.pluglesspower.com/learn/plugless-glance-guide-bmw-i3/


Guest

Fri Jan 06, 2017 8:30 am   



On Thu, 5 Jan 2017 21:21:00 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/05/2017 08:53 PM, krw_at_notreal.com wrote:
On Thu, 5 Jan 2017 14:46:04 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/05/2017 01:53 PM, John Larkin wrote:
On Thu, 5 Jan 2017 10:24:01 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Thursday, January 5, 2017 at 12:42:48 PM UTC-5, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some orders of
magnitude, so I'm considering using one or more photovoltaic cells with
one or more LEDs shining on them. It's all in an enclosure, so there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW? I guess blue LEDs
would be best? An efficiency of 1% (a 3W input) would be fine, even a
bit less. Just musing at the moment and if anyone has any ball-park
feelings or experience that would be good.

Cheers
--
Clive

There are high isolation DC-DC converters out there, not cheap, but ultimately superior to a photvoltaic system.
http://www.mouser.com/search/Refine.aspx?Keyword=164194258&Ns=Pricing%7c0&FS=True&Ntk=P_MarCom

A home-made inductive coupling thing wouldn't be difficult. It could
work through a piece of plexiglas for visible isolation, or just be
traces on opposite sides of a PC board. That could be really cheap in
production.

Or wind a ferrite toroid to make a transformer, and use really well
insulated wire.

But as you say, it's a lot easier to buy an appropriate dc/dc
converter.

For uA of current using a stack of photodiode optocouplers could work,
but for mA inductive coupling is likely the way to go.

The Starbucks near me has those "Powermat" chargers where you stick an
inductor ring to your phone's charging port and lay it on the inductor
ring on the table; I guess they chop the AC up to a high enough freq
that air makes a decent enough core, and a loop only slightly larger
than a quarter can transfer enough energy to charge up a smartphone in
under an hour

My last couple of phones have had this built in. It's know as Xi
(pronounced "chee"). I "hang up" my cell phone on one when I get
home.


If you're the type of plug-in hybrid driver who finds it just too
burdensome to plug in a cable, you can even have one for your car. ;-)

https://www.pluglesspower.com/learn/plugless-glance-guide-bmw-i3/


It's not that it's a burden. Micro-Bs have a limitied life. I'd
rather charge it, every day, with the Xi xharger than cycle the
connector another time. Sure, I'd like to have one in the car, too.
You'll see more of them in cars, soon.

It's amazing that Apple didn't pick up the technogy. I probably would
have gone with an iPhone when I got my current phone if they had Xi.


Guest

Fri Jan 06, 2017 8:30 am   



On Thu, 5 Jan 2017 14:46:04 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/05/2017 01:53 PM, John Larkin wrote:
On Thu, 5 Jan 2017 10:24:01 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Thursday, January 5, 2017 at 12:42:48 PM UTC-5, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some orders of
magnitude, so I'm considering using one or more photovoltaic cells with
one or more LEDs shining on them. It's all in an enclosure, so there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW? I guess blue LEDs
would be best? An efficiency of 1% (a 3W input) would be fine, even a
bit less. Just musing at the moment and if anyone has any ball-park
feelings or experience that would be good.

Cheers
--
Clive

There are high isolation DC-DC converters out there, not cheap, but ultimately superior to a photvoltaic system.
http://www.mouser.com/search/Refine.aspx?Keyword=164194258&Ns=Pricing%7c0&FS=True&Ntk=P_MarCom

A home-made inductive coupling thing wouldn't be difficult. It could
work through a piece of plexiglas for visible isolation, or just be
traces on opposite sides of a PC board. That could be really cheap in
production.

Or wind a ferrite toroid to make a transformer, and use really well
insulated wire.

But as you say, it's a lot easier to buy an appropriate dc/dc
converter.

For uA of current using a stack of photodiode optocouplers could work,
but for mA inductive coupling is likely the way to go.

The Starbucks near me has those "Powermat" chargers where you stick an
inductor ring to your phone's charging port and lay it on the inductor
ring on the table; I guess they chop the AC up to a high enough freq
that air makes a decent enough core, and a loop only slightly larger
than a quarter can transfer enough energy to charge up a smartphone in
under an hour


My last couple of phones have had this built in. It's know as Xi
(pronounced "chee"). I "hang up" my cell phone on one when I get
home.

rickman
Guest

Fri Jan 06, 2017 4:26 pm   



On 1/5/2017 9:21 PM, bitrex wrote:
Quote:
On 01/05/2017 08:53 PM, krw_at_notreal.com wrote:
On Thu, 5 Jan 2017 14:46:04 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/05/2017 01:53 PM, John Larkin wrote:
On Thu, 5 Jan 2017 10:24:01 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Thursday, January 5, 2017 at 12:42:48 PM UTC-5, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various
solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some
orders of
magnitude, so I'm considering using one or more photovoltaic cells
with
one or more LEDs shining on them. It's all in an enclosure, so
there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't
in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW? I guess
blue LEDs
would be best? An efficiency of 1% (a 3W input) would be fine,
even a
bit less. Just musing at the moment and if anyone has any ball-park
feelings or experience that would be good.

Cheers
--
Clive

There are high isolation DC-DC converters out there, not cheap, but
ultimately superior to a photvoltaic system.
http://www.mouser.com/search/Refine.aspx?Keyword=164194258&Ns=Pricing%7c0&FS=True&Ntk=P_MarCom


A home-made inductive coupling thing wouldn't be difficult. It could
work through a piece of plexiglas for visible isolation, or just be
traces on opposite sides of a PC board. That could be really cheap in
production.

Or wind a ferrite toroid to make a transformer, and use really well
insulated wire.

But as you say, it's a lot easier to buy an appropriate dc/dc
converter.

For uA of current using a stack of photodiode optocouplers could work,
but for mA inductive coupling is likely the way to go.

The Starbucks near me has those "Powermat" chargers where you stick an
inductor ring to your phone's charging port and lay it on the inductor
ring on the table; I guess they chop the AC up to a high enough freq
that air makes a decent enough core, and a loop only slightly larger
than a quarter can transfer enough energy to charge up a smartphone in
under an hour

My last couple of phones have had this built in. It's know as Xi
(pronounced "chee"). I "hang up" my cell phone on one when I get
home.


If you're the type of plug-in hybrid driver who finds it just too
burdensome to plug in a cable, you can even have one for your car. ;-)

https://www.pluglesspower.com/learn/plugless-glance-guide-bmw-i3/


They don't talk about efficiency, but the charging rate is lowered by
20% so I assume the efficiency is 20% lower.

--

Rick C

Chris Jones
Guest

Sat Jan 07, 2017 8:30 am   



On 06/01/2017 04:42, Clive Arthur wrote:
Quote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

It's too much power for normal photovoltaic isolators by some orders of
magnitude, so I'm considering using one or more photovoltaic cells with
one or more LEDs shining on them. It's all in an enclosure, so there's
no significant ambient light. The cell(s) could be several square
centimeters area. I like this arrangement as the isolation isn't in any
doubt - there could be centimetres of gap.

What sort of size cells would I need for around 30mW?

The size of the cells required depends entirely on the intensity of the
light hitting them. At "1 sun" illumination you get close to 40mA per
cm2 area, but then you need probably 6 cells that size to get 3V output.
The level of illumination producing an output power equivalent to what
you get with sunlight might be quite a bit less than the power density
of sunlight (which is about 1kW/m2), if you choose the wavelength that
is used most efficiently by the PV cell.

The efficiency of ordinary silicon PV cells is pretty much independent
of light level up to a couple of suns at least. By keeping the light
concentrated (e.g. acrylic light pipe) you could use a very small cell,
or with exactly the same light source you could let the light spread out
and then you would need a bigger PV cell to collect the same amount of
light.

Taken to an extreme, if money were no object then you could use a 3W
laser diode coupled to an optical fibre (e.g. Osram SPL 2F81-2S) as your
illumination source. Even a very small cell could be used to convert the
light back to electricity, if you can find a cell that can handle such
concentrated illumination. If you wanted to use ordinary "1-sun" solar
cells then you would instead need to let the output of the optical fibre
diverge until the intensity is in the range of a few suns or less.

It is possible to achieve somewhat higher efficiencies at more than 1
sun of illumination, if the cells are designed for that (e.g. with
beefed up metal contacts for less resistance, and other optimisations).
If the cells designed for 1-sun use have a lot of internal series
resistance then this will drop too much voltage at high current
densities (many suns of illumination). Some cells are designed for
operation at tens or hundreds or even thousands of suns of concentrated
illumination but they are probably hard to obtain.

At low intensities you could probably use BPW34 photodiodes as solar
cells. I am not sure how much series resistance they have so you would
need to check that to see what is the sensible maximum current you can
use them at. Into a short-circuit they produce about 2.8mA under
sunlight, but I have not tried to use them near the maximum power point,
and the series resistance could limit the power available. The advantage
of these photodiodes over solar cells is the small size and easy PCB
mounting.

Quote:
I guess blue LEDs
would be best?
As others pointed out already, IR LEDs will be best. e.g. SFH4725S


If you use more than one PV cell in series so that you can get your 3V
output, then the current available will be limited to that produced by
the weakest (least-illuminated) cell. Therefore you might have to either
over-illuminate them all a bit, or put some attention into the optical
arrangement so that you will be illuminating the PV cells equally.

Also:
If you want to simplify the PV cell part so that you don't need many PV
cells in series but could just use a single PV cell, then you could
modulate the IR LED, and shine that onto a single PV cell generating a
modulated current at up to about 0.5V. You can then feed the PV cell
output directly into a step-up transformer to whatever rail voltages you
require. You could also have two IR LEDs and two solar cells connected
in anti-parallel, if you wanted a push-pull current waveform driving the
transformer primary.

Chris Jones
Guest

Sat Jan 07, 2017 8:30 am   



On 06/01/2017 10:32, whit3rd wrote:
Quote:
On Thursday, January 5, 2017 at 9:42:48 AM UTC-8, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA on the high
side of a several kilovolt supply. I know there are various solutions,
but I'd like to use a 'solar cell' to supply isolated power.

What sort of size cells would I need for around 30mW? I guess blue LEDs
would be best?

Not blue;; go for infrared. The sensitivity peak for silicon is 900-1000 nm,
and blue (420 nm) loses by a factor of two or three.

http://www.bentham.co.uk/pdf/PV_Technical_Note.pdf

The mass-produced remote control LEDs are possibly your best bet;
perhaps Vishay TSAL6100. They will probably need some heatsinking,
if the rated 100 mA is applied.


These days you can do much better than the IR remote control ones. Look
at the ones designed for IR illumination for security cameras, e.g.
http://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/SFH-4725S/475-3012-1-ND/3767470

Winfield Hill
Guest

Sat Jan 07, 2017 7:04 pm   



Chris Jones wrote...
Quote:

On 06/01/2017 10:32, whit3rd wrote:
On Thursday, January 5, 2017, Clive Arthur wrote:
I want to run a microcontroller circuit at about 3V 10mA
on the high side of a several kilovolt supply. I know
there are various solutions, but I'd like to use a
'solar cell' to supply isolated power.

These days you can do much better than the IR remote
control ones. Look at the ones designed for IR
illumination for security cameras, e.g.
http://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/SFH-4725S/475-3012-1-ND/3767470


I'd be very interested to see how well that one does.


--
Thanks,
- Win

whit3rd
Guest

Sun Jan 08, 2017 5:35 am   



On Friday, January 6, 2017 at 9:11:21 PM UTC-8, Chris Jones wrote:

Quote:
If you want to simplify the PV cell part so that you don't need many PV
cells in series but could just use a single PV cell, then you could
modulate the IR LED, and shine that onto a single PV cell generating a
modulated current at up to about 0.5V.


Yeah, the about-half-a-volt per photovoltaic diode is a killer.
Probably best to use a center-tapped transformer driven by two
PV solar cells, and feed constant current through two IRLEDs in
series, shorting one at a time. That way the output can be
nearly constant, AND the light-source drain is also nearly constant.

Hopefully, the PV cells are not so capacitive that the frequency
has to be kept low.


Guest

Sun Jan 08, 2017 8:30 am   



On Sunday, 8 January 2017 03:35:32 UTC, whit3rd wrote:
Quote:
On Friday, January 6, 2017 at 9:11:21 PM UTC-8, Chris Jones wrote:

If you want to simplify the PV cell part so that you don't need many PV
cells in series but could just use a single PV cell, then you could
modulate the IR LED, and shine that onto a single PV cell generating a
modulated current at up to about 0.5V.

Yeah, the about-half-a-volt per photovoltaic diode is a killer.
Probably best to use a center-tapped transformer driven by two
PV solar cells, and feed constant current through two IRLEDs in
series, shorting one at a time. That way the output can be
nearly constant, AND the light-source drain is also nearly constant.

Hopefully, the PV cells are not so capacitive that the frequency
has to be kept low.


I vaguely recall polycrystalline cells being very slow. Someone might correct me though.


NT

Chris Jones
Guest

Sun Jan 08, 2017 7:25 pm   



On 08/01/2017 14:35, whit3rd wrote:
Quote:
On Friday, January 6, 2017 at 9:11:21 PM UTC-8, Chris Jones wrote:

If you want to simplify the PV cell part so that you don't need many PV
cells in series but could just use a single PV cell, then you could
modulate the IR LED, and shine that onto a single PV cell generating a
modulated current at up to about 0.5V.

Yeah, the about-half-a-volt per photovoltaic diode is a killer.
Probably best to use a center-tapped transformer driven by two
PV solar cells, and feed constant current through two IRLEDs in
series, shorting one at a time. That way the output can be
nearly constant, AND the light-source drain is also nearly constant.

Hopefully, the PV cells are not so capacitive that the frequency
has to be kept low.


Good point. I think the high efficiency cells like Sunpower have quite a
bit of capacitance. If one wanted to use modulated IR and a transformer
after the PV cells, that would be one reason to prefer an optical system
that can apply concentrated light to the PV cells - then the PV cells
could be small and therefore would have low capacitance.

Bearing in mind the issue of capacitance, perhaps 6 cells in series is a
better idea.

whit3rd
Guest

Mon Jan 09, 2017 1:08 am   



On Sunday, January 8, 2017 at 4:25:25 AM UTC-8, Chris Jones wrote:
Quote:
On 08/01/2017 14:35, whit3rd wrote:
On Friday, January 6, 2017 at 9:11:21 PM UTC-8, Chris Jones wrote:

If you want to simplify the PV cell part so that you don't need many PV
cells in series...

Yeah, the about-half-a-volt per photovoltaic diode is a killer.
Probably best to use a center-tapped transformer driven by two
PV solar cells...
Hopefully, the PV cells are not so capacitive that the frequency
has to be kept low.

Bearing in mind the issue of capacitance, perhaps 6 cells in series is a
better idea.


The problem, then, is balancing the six cells in series so one of 'em isn't
a weak link. With square cells, you could aim at a four-corners spot
and infer balance from symmetry.

Chris Jones
Guest

Mon Jan 09, 2017 8:30 am   



On 09/01/2017 10:08, whit3rd wrote:
Quote:
On Sunday, January 8, 2017 at 4:25:25 AM UTC-8, Chris Jones wrote:
On 08/01/2017 14:35, whit3rd wrote:
On Friday, January 6, 2017 at 9:11:21 PM UTC-8, Chris Jones wrote:

If you want to simplify the PV cell part so that you don't need many PV
cells in series...

Yeah, the about-half-a-volt per photovoltaic diode is a killer.
Probably best to use a center-tapped transformer driven by two
PV solar cells...
Hopefully, the PV cells are not so capacitive that the frequency
has to be kept low.

Bearing in mind the issue of capacitance, perhaps 6 cells in series is a
better idea.

The problem, then, is balancing the six cells in series so one of 'em isn't
a weak link. With square cells, you could aim at a four-corners spot
and infer balance from symmetry.


If efficiency is not an important consideration then it doesn't matter
if some of the cells are over-illuminated, as long as the
least-illuminated one receives enough light to supply the output current
required. Therefore the problem of non-uniform illumination could be
solved by increasing the current through the LED, or adding more LEDs.

Clive Arthur
Guest

Wed Jan 11, 2017 1:15 am   



Thanks, all, there's been some useful discussion here. If it proceeds,
I'll post results.

Cheers
--
Clive

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