Precision Photodiode comparator

Hello Julien,

The LM311 is a RoHS alternative part to the LM111.

The datasheet was written nearly 30 years ago and we don't have any further detials on this application. Depending on what you are trying to implement there might be a more modern solution availible...

Hope this helps

Thomas

Hello Tomas,

I am trying to implement a plasma detector (in a black tank) but I have to made it compact.

I already find a way with three stages : a photodiode preamplifier, a non inverter amplifier (G=3) and a non inverter comparator to have a TTL output.

However, I would be pleased if you have a smaller way to implement it.

Julien

Julien;

In order to help you it is necessary to know the bandwidth that you need for the amplifier, the input signal current, and any other parameters that you may have.

I used TLC277CD operational amplifiers with a single 5V supply.

The maximum output swing bandwidth is BOM = 320kHz and the Unity gain bandwidth is B1=1.7MHz but the photodiode signal input will be a low frequency.

I used a DPW34 photodiode with a photocurrent Ip=80uA

Julien;

The bandwidth you need is ? "Low frequency" is not too specific. I cannot find a "DPW34"-- who makes this photodiode. Is there a certain input signal level that you need the comparator to trigger on?

Sorry, I made a mistake it's a BPW34 from OSRAM. Actually, I don't really know how to define the bandwidth. It's for a detection not communication (ON/OFF).

Julien;

If you are simply sensing the presence of light, your bandwidth requirement will be minimal and this simplifies the required circuit considerably.

A precision op amp such as an OPA335 can be used as a comparator; its output will be TTL-compatible when it is operated on a single 5V supply. Speed is no problem so an op amp without feedback works as a comparator just fine. Here is a TINA circuit that should work with 80uA from your photodiode-- it triggers on 24uA.

Use TINA-TI v9 to open it.

Thank you for your help.

It works well with R2=100k and I also added two resistors to make an hysteresis.

I still have another question : What is difference between the OPA335AIDBVT and OPA335AIDBVTG4?

Julien,

The G4 suffix indicates that the part is lead-free. Today, both versions are lead-free. When lead-free requirements were new, we needed separate part numbers to assure customers that customers that they were receiving a lead-free parts. We have kept both designations so that customer's documentation does not need to be changed.

There are no electrical differences.

Regards, Bruce.