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Photodiodes saturating in ambient light

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T3sl4co1l:
That's why I said use an inductance, or something emulating it -- the resistor allows the photodiode to saturate and the gain drops towards zero.

Tim

twospoons:
In a previous job I built an IR laser receiver using BPW34s that could detect a 1pJ pulse in full sun. Your pulse is ~10nJ, so it should be fairly easy. The circuit used the BPW34s in photovoltaic mode (no bias) and fed the photocurrent through a small pulse transformer to remove the DC current produced by ambient light. There was a fairly high gain pulse amplifier after that, built using BFT92 BJTs.

If you dont want to use photovoltaic mode, which can be a bit slower, then you might want to try using a gyrator as the bias load (one BJT, one cap, one resistor).
Both methods shown below, but ignore the component values - they're just the schematic editor defaults.

David Hess:

--- Quote from: aussie_laser_dude on May 10, 2020, 02:28:29 pm ---a dc restoration loop? I'll investigate that.
--- End quote ---

If the photodiode amplifier is inverting, then an integrator which is also inverting can compare the output to zero and subtract a current from the input to stabilize the output.  This produces a high pass response from the integrator's low pass response.

https://e2e.ti.com/support/amplifiers/f/14/t/300533?AC-Coupled-Photodiode

This integrator trick also works with instrumentation amplifiers to produce a high pass response.

aussie_laser_dude:
Thanks for the messages guys, lots of info to take in. Sorry i messed up my terminology, i've used reverse bias mode and also photovoltaic mode (not photoconductive). Both circuits have similar outputs in sunlight, but the reverse bias circuit has a much stronger signal in the shade. Should fully understand the battery/resistor saturation theory later today after a few more tests, also nearly got a bjt pnp amplifier ready to test and op amps are in the mail so this is exciting!

Twospoons, was the IR wavelength of your device above 800nm? It's got quite impressive specs for being bathed in sunlight, i'm guessing the design had an optical low pass / bandpass filter?

StillTrying:
All you've got to do to prevent saturating is to lower the 13k to about 2k2.

Start simple to find out what the photo diode's output current is.
https://www.eevblog.com/forum/beginners/more-help-with-ir-photo-diodes-please/msg3035868/#msg3035868

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