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In my design, a photo diode is connected in reverse bias with 12V. The LDO (low-dropout) voltage regulator which is used for biasing can deliver a maximum current of 500mA

My configuration:

schematic

simulate this circuit – Schematic created using CircuitLab

What I want to know is: If my photo diode gets saturated, how would it behave? Will it behave like a current source generating maximum rated current? or a short circuit allowing 500mA of supply current directly to the TIA (transimpedance amplifier)?

I'm asking because I want to put a protection diode before the TIA, which has maximum rated input current of 100mA.

I want to know the equivalent circuit of a saturated photo diode - is it a closed switch or a regulated current source?

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OP: "...please explain how would a photo diode behave in saturation which would explain my doubt in total, is it like a close switch or a constant current source with current being peak current"

A quick Google gave me two useful results:

"Once the Saturation point is reached, the behavior of the photodiode becomes more and more non-linear until the Damage threshold point is reached. At this point the photodiode is no longer able to turn excess in incident optical power into a photocurrent output and all the extra energy received by the device would be absorbed, typically as heat. This heat inside the device can easily damage it irreversibly as it endangers the fragile wire bonds on the surface of the photodiode."

Source: http://www.osioptoelectronics.com/technology-corner/frequently-asked-questions/input-light-intensity.aspx


"As the photocurrent increases, first the non-linearity sets in, gradually increasing with increasing photocurrent, and finally at saturation level, the photocurrent remains constant with increasing incident light power."

Source: http://www.osioptoelectronics.com/application-notes/an-photodiode-parameters-characteristics.pdf


PS: Seems that the question is too old. I have no idea why it appeared in recent questions. Maybe a Community edit...

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Are you sure this is really an issue? Even a large-area PD might require something like 1W of light power on the chip to get to hundred of mA of photocurrent. Dissipation at the sensor might be more of an issue if it's sustained.

Also, if you exceed the 100mA current, the TIA should simply saturate at the maximum output voltage meaning the input will go above ground, which should not damage anything. The PD can't supply current without bound on the output (compliance) voltage- it is limited to the voltage on the regulator so the worst it could do is effectively connect the TIA input to the +5.

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  • \$\begingroup\$ my photo diode has maximum response of 0.7A/W , if you think this is high, there are avalanche photo diodes which can produce much high current as the responsivity being 100A/W, so high current is possible, if excess current is given as input to TIA there is voltage that should not be exceeding at input of opamp, if exceeded may damage opamp, it varies with opamp, for example see LTC6269-10 which has limit of +2V at input terminal \$\endgroup\$ – kakeh Aug 13 '16 at 7:21
  • \$\begingroup\$ what i infact want to know is the equivalent circuit of a saturated photo diode, will it be a closed switch or a regulated current source \$\endgroup\$ – kakeh Aug 13 '16 at 7:22
  • \$\begingroup\$ please explain how would a photo diode behave in saturation which would explain my doubt in total, is it like a close switch or a constant current source with current being peak current \$\endgroup\$ – kakeh Aug 22 '16 at 10:05

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