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'[EE]: LED as a photodiode- theory! Please help wit'
2001\06\06@185855 by Saurabh Sinha

picon face
Hi again,

Thank you for your replies to my question thus far. Advise me on the
following by choosing the most correct answer. I think it is [2] or [3].

If I have two LEDs that are radiating each other from a distance of approx.
1mm and both are driven by current sources, then:
1. The diodes will become unstable
2. Electrical power to diodes will increase
3. Voltage across diodes will increase
4. Light output of both diodes will increase
5. Light output of both diodes will decrease

Thanks.

Regards,

S. Sinha (Saurabh)
Tel/Fax: (012) 343-4912
Cell: 0825405577
E.Mail: spam_OUTssinhaTakeThisOuTspamIEEE.ORG
Visit: http://home.mweb.co.za/si/sinha [Home]
Visit: http://ieee.up.ac.za/members/saurabhs [Work] [Underconstruction]
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ICQ: 82010326

{Original Message removed}

2001\06\07@172537 by Chris Carr

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face
I haven't the time to give you an answer but I tell you what I will do for
you . I will pass this posting onto my 12 year old nephew with a few
components and some test equipment and see what answer he comes up with for
you. I'm sure he will be able to come up with something over the weekend in
between doing his homework from school.

Chris Carr

> Hi again,
>
> Thank you for your replies to my question thus far. Advise me on the
> following by choosing the most correct answer. I think it is [2] or [3].
>
> If I have two LEDs that are radiating each other from a distance of
approx.
{Quote hidden}

> {Original Message removed}

2001\06\08@120652 by Olin Lathrop

face picon face
> Thank you for your replies to my question thus far. Advise me on the
> following by choosing the most correct answer. I think it is [2] or [3].
>
> If I have two LEDs that are radiating each other from a distance of
approx.
> 1mm and both are driven by current sources, then:
> 1. The diodes will become unstable
> 2. Electrical power to diodes will increase
> 3. Voltage across diodes will increase
> 4. Light output of both diodes will increase
> 5. Light output of both diodes will decrease

I admit that I don't actually know this answer, but I suspect that you won't
see much of any measurable difference to a first approximation.  Of course
if you really want to know, don't ask, do it!  I'd like to hear the answer
when you find out.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\06\09@041012 by Peter L. Peres

picon face
The only one I can be sure of is > 1. The diodes will become unstable and
the answer is NO. Because the quantic efficiency is subunitary in both
directions (emit and photovoltaic) there will not be enough gain for any
instability to occur.

I also think that you will need some fancy instruments to check this,
because the efficiency of LEDs is very low (in both directions) and
whatever change you will observe will be attenuated by this efficiency,
squared.

Peter

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2001\06\12@033336 by Maurizio Viterbini

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face
Olin Lathrop wrote:
>
> > Thank you for your replies to my question thus far. Advise me on the
> > following by choosing the most correct answer. I think it is [2] or [3].
> >
> > If I have two LEDs that are radiating each other from a distance of
> approx.
> > 1mm and both are driven by current sources, then:
> > 1. The diodes will become unstable
> > 2. Electrical power to diodes will increase
> > 3. Voltage across diodes will increase
> > 4. Light output of both diodes will increase
> > 5. Light output of both diodes will decrease
>
> I admit that I don't actually know this answer, but I suspect that you won't
> see much of any measurable difference to a first approximation.  Of course
> if you really want to know, don't ask, do it!  I'd like to hear the answer
> when you find out.
>
from "circuits idea" Colin Pye ELECTRONIC WORLD may 2001

1 2             100k
2 0             22k
3 2             LED
2 0             100n
3 2             1M
3 2             1n
2 4             10k
4 5             1M
4 5             100n
3 4 7 0 5 TLo81 +in -in + - out

with a short description of the behavior with various LED colours in
photovoltaic mode.

> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, EraseMEolinspam_OUTspamTakeThisOuTembedinc.com, http://www.embedinc.com
>
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> ways.  See http://www.piclist.com/#archives for details.

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Maurizio Viterbini
Istituto di Fisica dell'Atmosfera
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00133 Roma
Italy

tel. +39 06 49934200
fax +39 06 20660291
email viterbinspamspam_OUTifa.rm.cnr.it

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