Electrical Engineering Stack Exchange
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Questions tagged [photodiode]

A photodiode converts light to an electric current.

A photodiode creates a current proportional to illuminance when light falls on it. We distinguish between visible light and infrared (IR) photodiodes. A phototransistor integrates a transistor with the diode to increase sensitivity.

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Does this photodiode circuit work?

Oli used this circuit in an answer, and it pops up a lot on Google images too. But does it work? If it does a theoretical explanation will be welcome.
stevenvh
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What was used to detect light before the invention of photodiodes/phototransistors?

Were there technologies before photodiodes/phototransistors or similar semiconductors, which could be used to start or stop machinery based on the amount (or presence/absence) of light falling on them?
vsz
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Photodiode amplifier circuits - why use an op amp instead of just a resistor?

Beginner question here. I've built a photodiode light sensing circuit in class and internship such as this one: I don't understand what it is doing over a simple circuit such as this one: Can anyone help me out?
Eddie Huang
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Forward drop of diode vs forward drop of LED

It is always said that forward voltage drop in the diode is around 0.7 volts. LED also being a diode, why does it have a greater forward voltage drop of around 3 Volts? What is the model of LED that explains this higher voltage drop?
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What causes the trough of a sine wave to become sharp?

I am using a white LED to send a 5 V p-p: +2.5 V to +7.5 V, DC offset of 5 V, sine wave of frequency 1 kHz as shown in the transmitter circuit. The current generated by the photodiode is converted to voltage using the load resistor. The receiver…
rockky007
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How do I connect a photodiode?

I'm trying to design a circuit to measure the ambient visible light (380nm to 750nm). Accuracy isn't too important. I've been looking at photodiodes, but I'm not sure how to connect them up. I need the following requirements from my circuit: low…
Eamorr
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Why does the voltage of the photodiode "bounce"?

I have setup a BPW-21 photodiode as shown below: The photo-diode is activated by an oscillating laser beam. I expected to get a clean +5V to 0V transition at point A when the laser beam falls on the photodiode and a 0V to +5V transition when the…
Abhishek
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How to Use SFH235 IR Photodiode Correctly?

I have an SFH235 ir photo-diode (which datasheet can be found here) and only basic knowledge of electronics. I want to connect the photodiode to an Arduino (the grand-plan is to add an ir diode and build a distance sensor). I understand that…
Artium
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Triggering generic transistors with UV or green light?

Flashes of UV light can create electron-hole pairs in transistors. Or at least reports of the "UV flash bug" claim this happens in microprocessors. People observed raspberry pies reset when subjected to a bright flash. I'd like to do a demonstration…
ions me
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Reducing noise in audio circuit (optical pickup + op amp)

I am building an optical pickup using a photodiode connected to a LM741 op-amp. My circuit is similar to this one: Except that I've added a passive high-pass filter after the output of the op-amp, to eliminate DC (since I am using 0V and +12V as my…
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Measuring light levels with a photodiode and an ADC

I'm trying to use a photodiode to measure light levels via an ADC on an ATMega168. I've got the microcontroller code working properly (measuring values on a pin and reporting it as an led brightness) but I'm having trouble getting the photodiode to…
wcmartin
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Photon count with ADC, am I doing it right?

I have this LED and I want to characterize this photodiode. The LED should produce light of 370 nm, but I measured it and it is around 358 nm, and at that wavelength the quantum efficiency (\$\eta\$) of the photodiode is 0.5141. Now, I feed the…
Fernando Franco Félix
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Why do we use an opamp to produce a voltage output above 1V in this circuit?

I wonder what advantages (regarding noise or other important factors) the opamp circuit: holds over a circuit consisting of only a photodiode and a resistor (the resistor has to be placed where the voltage (V) is): The math should be the…
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How to keep decompensated op amp in linear region?

Background For transimpedance applications, you want to keep op amps in their linear region and avoid op amp saturation and overdrive recovery. This can be done with a simple automatic gain control circuit when using a unity gain stable op amp…
DavidG25
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Adding Photodiode to LTspice

I am very new to LTspice. I would like to ask "How can I add a photodiode in the Ltspice?" Is ideal photodiode (or any specific) model already included in the LTspice or do I need to create third party model for photodiode? If it is already…
Sui
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