Loading effect problem

[MobiNaz]

Hello all,

I am trying to bias a diode by a photodiode under illumination. If I measure the voltage generated by the photo under laser illumination, it gives me 480mV.
But then I introduce the diode in parallel to the diode (thats how it is going to be)

Photo|| Diode

The voltage across the photo reduces to 200mV and the current is less then what I require. Reducing of photodiode's voltage indicates that the diode resistance is less than that of photodiode. But less current indicates that the diode resistance id high such that it draws less current.

How do I cater this problem?

Introduce a resistor in parallel such that I and V become what I require, increase the photodiode intensity or area, have I understood the problem correctly?



Thanks in advance.

 

[FvM]

The measurement suggests that most of the current available from the photodiode (short circuit current Isc) at the present illumination level is flowing through the diode.

So what's the exact problem? Are you expecting a higher Isc value or a different diode I/V characteristic?

 

[jiripolivka]

The best way is to use the two diodes (active and passive) connected to the opposite inputs of a fast opamp. Then they are not loaded and do not affect each other. You can use the "passive" diode to reduce ambient light effect if needed as well as achieve a temperature compensation.