I have a simple photodiode sensitive to a particular wavelength. I've noticed the following, for IDENTICAL lighting conditions for both situations described below:

- if I simply attach multimeter probes to either lead and measure current, I get around 760 uA.
- if, however, I add a load (10k) resistor between the two photodiode leads and insert my probes in series to measure photocurrent, I get only 50 uA.

Obviously, the photodiode has finite output power capability (i.e. you can't stick an infinite resistance between the leads and maintain the same current as zero resistance, but is there an equation characterizing the current/power output of a photodiode with respect to load resistance?

 

This https://www.thorlabs.com/tutorials.cfm?tabID=787382ff-26eb-4a7e-b021-bf65c5bf164b might help.

Your multimeter also likely has a resistors in it to measure current. So, you are effectively changing the load.

Modeling gets messy: http://www.jocet.org/vol4/323-S011.pdf

 

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Equivalent photodiode circuit consists of a semiconductor diode and current generator. The magnitude of the current is proportional to the illumination. You can make the measurements (enough 3 - 4 points), the current-voltage characteristics. Then find the spice model of the equivalent diode. To measure the current-voltage characteristics can use a voltage source, a variable resistor (10 kohm) and multimeter. Then you can use the Spice program. The conversion ratio is usually specified in datasheet.

 

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