Voltage output from photodiode in photovoltaic mode - diyAudio
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Old 14th January 2009, 07:39 PM   #1
bigwill is offline bigwill  United Kingdom
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Question Voltage output from photodiode in photovoltaic mode

Really simple question I've had surprisingly little luck getting the answer to from google:

What are the sort of voltages you can expect from a photodiode operated in photovoltaic mode?
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Old 15th January 2009, 03:16 AM   #2
jcx is offline jcx  United States
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the photocurrent forward biases the PN junction, flowing thru it in an internal loop following the ideal diode/shockley diode formula

for single crystal Si you might get .3 -.5V depending on illumination, light wavelength, temperature...

for linear measurement the photodiode is usually connected across the input of a transimpedance amp that holds the V to 0 so all of the photocurrent flows through the feedback R


you can get an optoisolator that stacks photodiodes in series to generate enough V to turn on a MOSFET
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Old 15th January 2009, 09:36 AM   #3
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But such voltage would be with picoamps of current (common diode). Even a DMM would load it down to a few microvolts if you tried to measure it.

Cheers!
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Old 15th January 2009, 04:19 PM   #4
bigwill is offline bigwill  United Kingdom
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Taking into account everything just said, I find it odd that I've been able to measure 1.2V from a normal red LED lit up brightly It even charged a 33uF electrolytic capacitor in about 15 seconds!
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Old 15th January 2009, 04:23 PM   #5
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Quote:
Originally posted by bigwill
Taking into account everything just said, I find it odd that I've been able to measure 1.2V from a normal red LED lit up brightly It even charged a 33uF electrolytic capacitor in about 15 seconds!
Different bandgap.
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Old 15th January 2009, 04:31 PM   #6
bigwill is offline bigwill  United Kingdom
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Well now I have found a fun floating bias source for MOSFETs without using batteries or expensive photovoltaic optocouplers
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Old 15th January 2009, 05:12 PM   #7
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Quote:
Originally posted by bigwill
Well now I have found a fun floating bias source for MOSFETs without using batteries or expensive photovoltaic optocouplers
I have never tried this myself. I would think, since white LED's use a secondary emission, they might only work as sources. BTW you can power over fiber optics with high powered lasers with 50% or more efficiency. There are safety issues.
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Old 15th January 2009, 05:14 PM   #8
bigwill is offline bigwill  United Kingdom
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Time to change my speaker cables to optical fibres and my amp to a modulated laser!
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Old 15th January 2009, 05:16 PM   #9
bigwill is offline bigwill  United Kingdom
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Regarding LEDs, I would use the exact same types for both the source and receiver
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Old 15th January 2009, 10:52 PM   #10
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I have actually used LEDs for a floating bias supply.
Figures a and d work in the real world.
The other figures are just wild lateral thinking on my part.
Probably not practical.

http://tinyurl.com/8wpwzl

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