# Designing an amplifier circuit for a BPW34 photodiode

I'm designing a laser seeker circuit. I need to amplify the photodiode so that the photodiode can detect laser beams reflected from the wall. I couldn't achieve this with the amplifier circuit you see below.

What should I change?

What are the shortcomings of my circuit?

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• How did you come up with this circuit? What is that circuit supposed to be? Because it looks like only part of a transimpedance amplifier. The photodiode is backwards and floating. And even if these issues were corrected, the capacitance is FAR too large and the resistance is FAR too low. May 26 at 16:23
• The + input of an LM358 has current that causes it to go towards the positive battery voltage. The negative feedback causes the output to try to go negative (the inverted voltage of the + ouput) so light on the diode might need to be blinding to cause a positive output from the opamp. May 26 at 16:30

## 2 Answers

Look at the circuits that I have here:

Assuming you're trying to make a transimpedance PD amplifier with the PD in photovoltaic mode:

You need a path for the currents. In this case, pin 3 and the PD should be grounded.

The PD is backwards.

220Ω is way too low. Likely you'll need more than 10kΩ. Maybe 100k-ish. A cursory glance at the PD datasheet will tell you that you get 47uA typically for a massive 1mW/cm^2 irradiance. Either calculate the light level if you are able or test it with a meter before "designing" something. You need numbers and the datasheets to design.