Voltage output from photodiode in photovoltaic mode

bigwill · 14th January 2009, 07:39 PM

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?

jcx · 15th January 2009, 03:16 AM

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

Geek · 15th January 2009, 09:36 AM

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!

bigwill · 15th January 2009, 04:19 PM

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!

scott wurcer · 15th January 2009, 04:23 PM

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.

bigwill · 15th January 2009, 04:31 PM

Well now I have found a fun floating bias source for MOSFETs without using batteries or expensive photovoltaic optocouplers

scott wurcer · 15th January 2009, 05:12 PM

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.

bigwill · 15th January 2009, 05:14 PM

Time to change my speaker cables to optical fibres and my amp to a modulated laser!

bigwill · 15th January 2009, 05:16 PM

Regarding LEDs, I would use the exact same types for both the source and receiver

zapnspark · 15th January 2009, 10:52 PM

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

Cheers.

ZAP

14th January 2009, 07:39 PM	#1
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	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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15th January 2009, 03:16 AM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	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

15th January 2009, 09:36 AM	#3
Geek diyAudio Member Join Date: Sep 2004	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!

15th January 2009, 04:19 PM	#4
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	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!

15th January 2009, 04:31 PM	#6
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Well now I have found a fun floating bias source for MOSFETs without using batteries or expensive photovoltaic optocouplers

15th January 2009, 05:14 PM	#8
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Time to change my speaker cables to optical fibres and my amp to a modulated laser!

15th January 2009, 05:16 PM	#9
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Regarding LEDs, I would use the exact same types for both the source and receiver

15th January 2009, 10:52 PM	#10
zapnspark diyAudio Member Join Date: Sep 2006 Location: Midwest	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 Cheers. ZAP

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