Need Help building Photo diode

Thread Starter

intel123

Joined Nov 1, 2011
3
Hi All,

I am novice in electronics. I am trying to build a simple photo diode circuit. I have a photo-diode SD 057-11-21-011. (Advance photonics) (It has fast onset i have been told). I am really thankful if someone can suggest me a circuit to build simple light detection circuit using this photo diode. I am trying to study timing delays between trigger generation and stimulus generation.

Thanks, Jinal.
 

wayneh

Joined Sep 9, 2010
16,114
You should add the word "circuit" to your title. More folks here know how to build circuits than how to build diodes. ;)

But maybe even before that you should poll for ideas to accomplish your goal, which should be clearly explained. You're going to need a lot more than a working photodiode, and the system should be blocked out end to end before you worry too much about the circuit details. I think there may be better, cheaper, simpler ways to accomplish your end goal.
 

Adjuster

Joined Dec 26, 2010
2,148
Let's keep this accurate, when advising a beginner: an ORP12 is a light dependant resistor, aka photo-resistor.

It is a viable light sensor, albeit rather slow to respond, but it is not a photo-diode.
 

Bernard

Joined Aug 7, 2008
5,285
I've never used a photo diode, but I believe it is used in a reverse biased mode; the more light the leakier it gets. Output is taker from a series load resistor. VCC to cathode, 10k anode to -[ ground], anode to one comparator input, 10 to 100 mV bias on other--or something like it.
 

MrChips

Joined Oct 2, 2009
19,383
Here is a start:



Play around with the value of R1 (10K to 10M ohms).
You can add an amplifier if you need to detect very low light levels.

Edit: Turn the diode around.
 
Last edited:

Adjuster

Joined Dec 26, 2010
2,148
It is often more convenient to take the output from a load resistor referenced to ground, even though this may tend to let in higher frequency noise from the supply through the diode capacitance.

At lower frequencies, a reverse biased photodiode tends to act as a current source, so taking the output across the diode you may see nearly the full extent of any power supply voltage variation. The DC output voltage seen across the diode is therefore not good as an indication of the mean optical input. The voltage across a load resistor is normally quite a good indication of the input level.

Photodiodes are typically used with reverse bias in applications where a fast response is required. Such bias minimises the junction capacitance and maximises the output current.

Some (but not all) photodiodes can generate an output current at zero bias, or even deliver a small positive voltage into a load resistor. This, after all, is the principle of the solar cell. Using a photodiode at zero bias can combat the effects of dark (leakage) current, but even with suitable devices the output may be a little less. The response tends to be slower due (among other things) to the diode capacitance being raised.

Specialised devices called Avalanche Photo Diodes (APDs) have an internal carrier multiplication process which increases their output when a critical high reverse bias is applied. These devices are rather difficult to use, non-linear and can be very noisy. They often require a minimum bias to respond at all, and personally I'd be happy to live out my days without ever seeing one again.

For circuits having a better speed/output voltage compromisethan the simple load resistance, try Googling "transimpedance": I may come back on this later but don'thave time for now. Good luck!
 

wayneh

Joined Sep 9, 2010
16,114
...please let me know what is the another alternate?
Describe, in as much detail as you can, what you hope to accomplish.
You mentioned "...trying to study timing delays between trigger generation and stimulus generation". But you didn't define what that means. You could be studying snails or whales for all we know.
 

Thread Starter

intel123

Joined Nov 1, 2011
3
I tried simple photodiode in reverse bias and connected it with 9v battery. Across 10K resistor I checked the output. I could see almost a 5V of jump on oscilloscope in signal when I flash a light in front of photo-diode.

If possible I also want to generate a trigger when light is detected by photo-diode. I am not sure how can I do it. If anyone have suggestion please let me know.
 
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