Using LEDs as photovoltaics

[Clive Arthur]

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable. I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about. Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first. I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better? In any event,
being able to see it working would be advantageous in this application.

Cheers
--
Clive

 

[Martin Brown]

On 07/11/2019 10:44, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

You are probably better off with a 3v silicon PV panel like the ones on
pocket calculators or garden lights at the receiving end. There was a
thread about this recently but with a higher current requirement.

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

Finding a way to drive it with a much smaller voltage might help.

--
Regards,
Martin Brown

 

[dcaster@krl.org]

On Thursday, November 7, 2019 at 5:44:40 AM UTC-5, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable. I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.
service
I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about. Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.
service
I'll need to do some experimenting, but I'd like to narrow things down a
bit first. I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better? serviceIn any event,
being able to see it working would be advantageous in this application.

Cheers
--
Clive

Have you considered the solar cells used to power calculators? Would probably take a couple in series to get 10 volts.

Dan

 

[Johann Klammer]

On 11/07/2019 11:44 AM, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to generate a small amount of isolated power - say to turn on a MOSFET not particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit more distance.]

I have read that you should use the same colour for drive and sense, which sounds reasonable. I imagine that higher Vf LEDs produce more V, but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and illuminating it with another gave me about 2V on my DMM, short circuit current too small to measure without fiddling about. Yes, I know the yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a bit first. I think the packaged photovoltaic isolators use IR LEDs, a guess based on their Vf - would blue LEDs be better? In any event, being able to see it working would be advantageous in this application.

Cheers

<https://www.circuitbread.com/ee-faq/the-forward-voltages-of-different-leds>
They say short wavelength UV have highest forward voltage.
I believe that's what will limit the output voltage.
also they'll pull down the gate ain when unpowered,
so maybe a si blocking diode might improve things(rev I in the uA range).
Esp if you plan to pulse the drive led above limit.

 

[Sjouke Burry]

On 07.11.19 13:46, dcaster@krl.org wrote:

On Thursday, November 7, 2019 at 5:44:40 AM UTC-5, Clive Arthur wrote:
An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable. I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.
service
I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about. Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.
service
I'll need to do some experimenting, but I'd like to narrow things down a
bit first. I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better? serviceIn any event,
being able to see it working would be advantageous in this application.

Cheers
--
Clive

Have you considered the solar cells used to power calculators? Would probably take a couple in series to get 10 volts.

Dan

Just break apart a garden light.
those element are meant to charge a 1,2 volt battery,
and can easily switch on any transistor(0.6-0.9volt).
I used it to switch a tr. to drive a relay for a nightlight.

 

[bitrex]

On 11/7/19 5:44 AM, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable.  I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about.  Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first.  I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better?  In any event,
being able to see it working would be advantageous in this application.

Cheers

Not quite sure what you mean by "need a bit more distance" here, is it
because the clearance between the package pins isn't enough on the
photoisolator, or because you can't place the isolator physically close
enough to the MOSFET for it to drive it effectively?

I think I've seen this done by taking an phototransistor like the 4N28
that brings the base terminal out to a pin, connecting the transistor as
a diode, and stacking them in series, at 10 volts probably good for
couple hundred uA with the IR diode string running full tilt.

But it sounds like maybe you want to shoot power across a gap of a
couple inches, or something.

 

[George Herold]

On Thursday, November 7, 2019 at 5:44:40 AM UTC-5, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable. I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

Is there some reason you can't use a photodiode as current generator?
(I guess you'd need more in series)
You might google Forest Mimms III who has done some led on led stuff.

In general I think you'll want the drive LED to be of a shorter
wavelength than the detector led. And beware of colored lens/ plastic.

George H.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about. Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first. I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better? In any event,
being able to see it working would be advantageous in this application.

Cheers
--
Clive

 

[Clive Arthur]

On 07/11/2019 15:53, George Herold wrote:

<snip>

Is there some reason you can't use a photodiode as current generator?
(I guess you'd need more in series)
You might google Forest Mimms III who has done some led on led stuff.

In general I think you'll want the drive LED to be of a shorter
wavelength than the detector led. And beware of colored lens/ plastic.

George H.

That seems right - my 'white' LED does nothing with either red or green
laser pen at point blank, but a small UV torch seems to give more output
than using a very bright white LED lamp as a source.


Cheers
--
Clive

 

[whit3rd]

On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

Receiver area is another concern; emitters are SMALL, most light aimed at 'em will miss.
The lenses help (small LEDs with narrow output for emitters, large LEDs with wide
output might be the best receivers). A silicon solar panel has the receive-area advantage,
it'll catch a lot more photons.

Lasers, even UV types, exist; you could use a laser to hit a small target, but it still
takes several receivers in series. Enough lasers to hit 10V worth of point receivers is going
to be pricey. Maybe a cluster of receivers around a phosphor dot, and laser-illuminate the dot?

 

[bitrex]

On 11/7/19 1:11 PM, whit3rd wrote:

On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

Receiver area is another concern; emitters are SMALL, most light aimed at 'em will miss.
The lenses help (small LEDs with narrow output for emitters, large LEDs with wide
output might be the best receivers). A silicon solar panel has the receive-area advantage,
it'll catch a lot more photons.

Lasers, even UV types, exist; you could use a laser to hit a small target, but it still
takes several receivers in series. Enough lasers to hit 10V worth of point receivers is going
to be pricey. Maybe a cluster of receivers around a phosphor dot, and laser-illuminate the dot?

EL backlight material and a PV cell might work over an inch or two

 

[Clive Arthur]

On 07/11/2019 18:11, whit3rd wrote:

On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

Receiver area is another concern; emitters are SMALL, most light aimed at 'em will miss.
The lenses help (small LEDs with narrow output for emitters, large LEDs with wide
output might be the best receivers). A silicon solar panel has the receive-area advantage,
it'll catch a lot more photons.

Lasers, even UV types, exist; you could use a laser to hit a small target, but it still
takes several receivers in series. Enough lasers to hit 10V worth of point receivers is going
to be pricey. Maybe a cluster of receivers around a phosphor dot, and laser-illuminate the dot?

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when illuminated
with a single UV LED from a torch. I'm guessing a blue LED receiver (ie
without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are narrow
band receivers, so I'm not sure why the UV LED works so well as a
source. It is partly visible with a sort of yellowish tinge.

Anyway, it seems it would work. Needs some experiments.

Cheers
--
Clive

 

[Rick C]

On Thursday, November 7, 2019 at 1:27:36 PM UTC-5, Clive Arthur wrote:

On 07/11/2019 18:11, whit3rd wrote:
On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

Receiver area is another concern; emitters are SMALL, most light aimed at 'em will miss.
The lenses help (small LEDs with narrow output for emitters, large LEDs with wide
output might be the best receivers). A silicon solar panel has the receive-area advantage,
it'll catch a lot more photons.

Lasers, even UV types, exist; you could use a laser to hit a small target, but it still
takes several receivers in series. Enough lasers to hit 10V worth of point receivers is going
to be pricey. Maybe a cluster of receivers around a phosphor dot, and laser-illuminate the dot?

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when illuminated
with a single UV LED from a torch. I'm guessing a blue LED receiver (ie
without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are narrow
band receivers, so I'm not sure why the UV LED works so well as a
source. It is partly visible with a sort of yellowish tinge.

I would not expect LEDs to be "narrow band". For a photon to be absorbed it would need to have sufficient energy. That equates to being short wavelength enough which is what George H said.

As others have pointed out the area of the receiving diode is rather small so it will be hard to gather enough energy. The IV curve should be fairly flat on both the current limited side and the voltage limited side with the max power point in the knee of intersection. Try reading the voltage under the load you will need.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[George Herold]

On Thursday, November 7, 2019 at 11:35:57 AM UTC-5, Clive Arthur wrote:

On 07/11/2019 15:53, George Herold wrote:

snip

Is there some reason you can't use a photodiode as current generator?
(I guess you'd need more in series)
You might google Forest Mimms III who has done some led on led stuff.

In general I think you'll want the drive LED to be of a shorter
wavelength than the detector led. And beware of colored lens/ plastic.

George H.

That seems right - my 'white' LED does nothing with either red or green
laser pen at point blank, but a small UV torch seems to give more output
than using a very bright white LED lamp as a source.

Right, The wavelength of light that is absorbed or emitted is a measure
of the bandgap in the semi conductor.

George H.

Cheers
--
Clive

 

[John Larkin]

On Thu, 7 Nov 2019 18:27:28 +0000, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 07/11/2019 18:11, whit3rd wrote:
On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

Receiver area is another concern; emitters are SMALL, most light aimed at 'em will miss.
The lenses help (small LEDs with narrow output for emitters, large LEDs with wide
output might be the best receivers). A silicon solar panel has the receive-area advantage,
it'll catch a lot more photons.

Lasers, even UV types, exist; you could use a laser to hit a small target, but it still
takes several receivers in series. Enough lasers to hit 10V worth of point receivers is going
to be pricey. Maybe a cluster of receivers around a phosphor dot, and laser-illuminate the dot?

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when illuminated
with a single UV LED from a torch. I'm guessing a blue LED receiver (ie
without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are narrow
band receivers, so I'm not sure why the UV LED works so well as a
source. It is partly visible with a sort of yellowish tinge.

Anyway, it seems it would work. Needs some experiments.

Cheers

Cree, and several other people, make "high voltage" multi-chip LEDs,
in white and blue and other colors, 12 to 48 volts. The 12v white ones
that I have look like welding torches.

Blue-to-blue 12 volts might work.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Thursday, 7 November 2019 19:11:11 UTC+1, whit3rd wrote:

On Thursday, November 7, 2019 at 2:44:40 AM UTC-8, Clive Arthur wrote:

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

Small power makes it sound easy, but 10V is rather hard; visible light
photons aren't so high energy, it mayl take a dozen receiver cells in series to hit
that target.

In another thread about the same subject, I had done some test. I could easily generate 2V on a LED, 5 in series is 10V

 

[Martin Brown]

On 07/11/2019 20:43, Rick C wrote:

On Thursday, November 7, 2019 at 1:27:36 PM UTC-5, Clive Arthur
wrote:
On 07/11/2019 18:11, whit3rd wrote:

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when
illuminated with a single UV LED from a torch. I'm guessing a blue
LED receiver (ie without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are
narrow band receivers, so I'm not sure why the UV LED works so well
as a source. It is partly visible with a sort of yellowish tinge.

I would not expect LEDs to be "narrow band". For a photon to be
absorbed it would need to have sufficient energy. That equates to
being short wavelength enough which is what George H said.

They are fairly narrow band with a typical FWHM of 50nm around their
nominal wavelength. You might get optimum performance with the emitter
wavelength slightly shorter than the detector. Possible for some "pure"
blues and greens these days.

It is a general rule that emitters at a particular frequency are also
good absorbers at that frequency when illuminated.

As others have pointed out the area of the receiving diode is rather
small so it will be hard to gather enough energy. The IV curve
should be fairly flat on both the current limited side and the
voltage limited side with the max power point in the knee of
intersection. Try reading the voltage under the load you will need.

I like JL's idea of a single compound blue LED with 12v nominal drop.

--
Regards,
Martin Brown

 

[Clive Arthur]

On 07/11/2019 23:46, John Larkin wrote:
<snipped>

Cree, and several other people, make "high voltage" multi-chip LEDs,
in white and blue and other colors, 12 to 48 volts. The 12v white ones
that I have look like welding torches.

Blue-to-blue 12 volts might work.

Thanks, I'll look into that. Not literally.

Cheers
--
Clive

 

[Clive Arthur]

On 07/11/2019 16:00, bitrex wrote:

<snipped>

Not quite sure what you mean by "need a bit more distance" here, is it
because the clearance between the package pins isn't enough on the
photoisolator, or because you can't place the isolator physically close
enough to the MOSFET for it to drive it effectively?

A visible gap and visible light is comforting when switching high
voltage, and makes for a simple 'mechanical' interlock.

But it sounds like maybe you want to shoot power across a gap of a
couple inches, or something.

A few mm would do.

Cheers
--
Clive

 

[Chris Jones]

On 07/11/2019 21:44, Clive Arthur wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable.  I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about.  Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first.  I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better?  In any event,
being able to see it working would be advantageous in this application.

Cheers

Could you use one modulated IR LED (e.g. SFH 4725S), driving one BPW34
photodiode that feeds a small step-up transformer and rectifier? It will
not be suitable for turning the output voltage on or off quickly as the
smoothing cap after the rectifier will slow things down. You can also
have two photodiodes in anti-parallel for push-pull drive to the step-up
transformer but you'd have to illuminate them with two LEDs in anti-phase.

 

[Clive Arthur]

On 08/11/2019 13:51, Rick C wrote:

<snipped>

I like the idea of using some photocells, but the world is a strange place.

Farnell and RS don't seem to sell anything suitable, which indicates
they're a bit hard to find. I suspect they'd be quite big too.

LEDs are easy to find, so if they work well enough...

Cheers
--
Clive