Electronics > Beginners

Photodiode circuit design

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StillTrying:
I've found the light shape from reds to be slower and curved, and super bright green and blue the fastest and squarest.
I won't be trying to get the fastest speeds out of the green and blues because I've got a 100W white COB waiting for >>100W testing!

jlmoon:
Just a curious question, how come you're setting the gain on 2nd op amp to 6.8?  Wouldn't it be ok to set that to unity or 1?  Using the 2nd amp as a follower or buffer only?

stcoso:

--- Quote from: StillTrying on March 30, 2019, 07:40:00 pm ---I've found the light shape from reds to be slower and curved, and super bright green and blue the fastest and squarest.
I won't be trying to get the fastest speeds out of the green and blues because I've got a 100W white COB waiting for >>100W testing!

--- End quote ---

I've tried also with some green led and found them slower. I used an IR led and it was the fastest.
I'm trying to build this little probe because i need it to measure a UV source (20W 365nm) that i've already built and rise/fall time are really important.

I suppose :D white LED are really bad (microseconds?) at turning on/off because of phosphorescence (turn off especially).

stcoso:

--- Quote from: jlmoon on March 30, 2019, 07:55:52 pm ---Just a curious question, how come you're setting the gain on 2nd op amp to 6.8?  Wouldn't it be ok to set that to unity or 1?  Using the 2nd amp as a follower or buffer only?

--- End quote ---


Short and thruthful answer: basically i don't know what i'm doing :-DD ... but, as i (maybe wrongfully :D) understood to achieve higher bandwidth without compromising stability and noise i needed lower gain in the first stage.


StillTrying:
"white LED are really bad (microseconds?) at turning on/off because of phosphorescence (turn off especially)."

As long as they're not warm white, white LEDs are faster than that ~160ns.
The last 2 pics in my link above reply#8 are RedGreenWhite5mm.gif and UV+Blue LED.gif  The UV edges are fast.

"Short and thruthful answer: basically i don't know what i'm doing"

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