Hello please help me! I am having trouble getting values for the equivalent circuit of a photodiode in zero bias. Lets say I would like to model this after the BPW34 photodiode, what commercially available values should I use for the capacitor and shunt resistance? And what diode should I use? The datasheet does not state the shunt resistance. Thank you!!

 

Hi otters,
Welcome to AAC.
Please post your LTSpice asc file.?
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Hi thanks for replying! Unfortunately I am unable to upload the asc file as the file location of the OPA380 i uploaded into the LTSpice is from my personal files and unauthorized personnel are unable to access it. Here is the file with a universal opamp instead

 

Hi otters,
I do not see the .asc file?

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Hi otters,
I do not see the .asc file?

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oh sorry! are you still unable to see it?

 

Hi otters.
In this .lib file look at Line #258
Use your Text editor to open and read it.

Let me know if you have a problem.
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Hi otters.
In this .lib file look at Line #258
Use your Text editor to open and read it.

Let me know if you have a problem.
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Thank you!!! so according to the model parameters, capacitance should be 72pF. However, I dont see a value for shunt resistance as well as which diode I should use.

 

Hi otters,
Look at this link showing the equivalent circuit.
I would be interested in seeing your final asc file.

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https://blog.mbedded.ninja/electronics/components/diodes/photodiodes/

 

Hi otters.
Also check out this Vishay BPW34 PDF
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Clip:
RS, and shunt resistance, Rsh, representing an additional leakage) can be neglected in most standard applications, and are not expressed in equations 5 and 7

 

Hi otters,
Look at this link showing the equivalent circuit.
I would be interested in seeing your final asc file.

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https://blog.mbedded.ninja/electronics/components/diodes/photodiodes/

View attachment 327144

thank you!! I see that this blog you sent me stated that the diode should be an ideal diode. isit possible to use a commercially available diode as I would need to simulate this circuit in real life in order to control the current as there is a photodiode prototype that will take its place eventually. Or is there any other way to control the photocurrent generated? the series resistance value stated in the Spice model is 0.1ohms. Will it be ok to ignore this resistor as when this resistor is added, the circuit becomes an inverting configuration instead of a transimpedance amplifier configuration and the gain will factor in this small resistor.

 

Spice model is 0.1ohms. Will it be ok to ignore this resistor as when this resistor is added, the circuit becomes an inverting configuration

Hi,
I would ignore a 0.1R series resistance value.
Redraw your LTSpice file and post a copy, let's see how it performs.
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hi otters,
Checkout this TI photodiode OPA.
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https://www.google.com/search?clien...ate=ive&vld=cid:5cf05a10,vid:EdX1MBvPMOw,st:0

 

Redraw your LTSpice file and post a copy, let's see how it performs.
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thank you for the advice! i have watched and read through all the links sent and this is my current design. Is there anything else i can do to improve the circuit?

 

Can quantify what optical quality you want to detect ? I need brightness wavelength and speed.

This may be done much better than what you posted.

 

Can quantify what optical quality you want to detect ? I need brightness wavelength and speed.

This may be done much better than what you posted.

Hi! Im trying to detect light under various conditions, up to 1 sun (1000W/m2), with a solar simulator. Wavelength is visible light, around 380nm to 700nm

 

Hi! Im trying to detect light under various conditions, up to 1 sun (1000W/m2), with a solar simulator. Wavelength is visible light, around 380nm to 700nm

That’s easy but how about using a log scale eye corrected spectrum over 5 decades using a single 5V LDO?
What viewing angle?

 

That’s easy but how about using a log scale eye corrected spectrum over 5 decades using a single 5V LDO?
What viewing angle?

Thank you for the suggestion! For the viewing angle the photodiode will be placed in a watch, hence the viewing angle is not constant. I think the suggested circuit will be a better option for my current project. I will research more and post another schematic soon!

 

I need help with another issue. Are my capacitor values too large? I am unsure on how to properly calculate the feedback capacitor

 

hi otters,
Try this method.
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Using negative feedback (NFB) with a single supply, you should have the anode grounded instead with a negative input cancelled by a positive output. You may use any yellow, red or IR chip LED to test your circuit. There is no need for capacitors unless you want them. All diodes have C (pF). F=1/(2pi RC)