I wanted to build low light UV detector, I mean the measurement of light with wavelength 405 nm. I found two schemes:

First circuit:


And the second circuit:


I wanted to use operational amplifier TLE2072CP and diode BPW21R. The bandwidth doesn't matter because I'll be observing light intensity which is DC level output voltage.

I wanted to use second op amp in TLE2072CP as non-inverting amplifier for additional signal amplification.

The circuit will be in shielding box, I assume in the second circuit, ground should be connected to shielding box, but I don't know what should be connected to shielding box in the first circuit.

Which of these two schemes will be better for my application?


Due to your suggestions, I've tried to plot second circuit: mycircuit link.

Some values and components are missing, how the circuit should look like?

  • 2
    \$\begingroup\$ Have you considered an optical (UV band pass) filter? After that it should be a matter of amplification and calibration. \$\endgroup\$
    – Abel
    Sep 17, 2022 at 3:26
  • 4
    \$\begingroup\$ The BPW21R is not sensitive to UV. It has been specifically constructed to be sensitive only to visible wavelengths as much as possible. Even it's unfiltered cousin, the BPW20R is not sensitive to UV due to the window material. Right now, GenUV available from Digikey seems to have the most easily available UV selective photodioes so no visible or NIR filters are required (which also oxidize from atmospheric moisture) which cuts down on cost a lot. The photodiodes can still be quite pricey though depending on the area you choose. From 2-5x the cost of your BPW21R with less active area. \$\endgroup\$
    – DKNguyen
    Sep 17, 2022 at 3:40
  • \$\begingroup\$ Those are both essentially the same circuit. The 1st one goes to a little more effort to split the supply rail to supply to the opamp's non-inverting input, but that's really the only difference between them. \$\endgroup\$
    – brhans
    Sep 17, 2022 at 3:59
  • \$\begingroup\$ What kind of UV light source are you expecting to measure? Many such sources are modulated,not nice and constant, because gas discharge isn't a stable process. \$\endgroup\$
    – Whit3rd
    Sep 17, 2022 at 5:25
  • \$\begingroup\$ The two circuits are electrically the same ... except for the reference point on BNC in the first (floating center point "not related" to the power supply). Note also that OPAMP decoupling capacitor not present ... \$\endgroup\$
    – Antonio51
    Sep 17, 2022 at 6:22


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.