The circuit is as follows

Photodiode transimpedance amplifier

I'm powering the op-amp from a 9V battery.

It gives me constant 3.6V at the output and it doesn't change with changing the illumination of the diode.

I tried replacing the 1M resistor with 10K and 10R, but it doesn't change anything.

I've double checked the pinout and it appears to be correct based on the datasheets that I can find.

The offset pins are floating in my circuit if this is of importance in this case.

When I swap LF356N with LM258N or CA3140 it works as expected with the output reacting to changes in the illumination.

What am I doing wrong?


LF356 is not a single-supply op-amp - ie. the input common mode range (and output swing with a load to the negative rail) do not include the negative rail. The CA3140 and LM358 are single-supply op-amps.

The op-amp in your circuit can only be in balance when both inputs are at the negative rail, hence it cannot work with the LF356. As you can see from the datasheet the op-amp needs the inputs to be at least 4 or 5V above the negative rail to be guaranteed to work properly. The output swing is a similar problem- it cannot approach the negative rail closer than a few volts, depending on the load.

enter image description here

If you add a negative supply (eg. -5V), just for the op-amp negative rail, it will work properly.

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  • \$\begingroup\$ How many times does this crop up....... \$\endgroup\$ – Andy aka May 1 '18 at 16:53
  • \$\begingroup\$ @Andyaka At least weekly I think. \$\endgroup\$ – Spehro Pefhany May 1 '18 at 16:54
  • \$\begingroup\$ Sorry, didn't know how to read the datasheet properly. \$\endgroup\$ – axk May 1 '18 at 17:01

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