I am working on a product requiring a photo sensor to detect white light, I need the largest possible dynamic range (1000:1 light levels) at the minimum cost.

Response time: 200 us rise/fall
Photo-conductive operation- (needs to sink current in proportion to light levels)
Long term / temp stability not required, device will autocal for every measurement.
No need for good linearity, I am not building a measuring device, just a lights on/off detector, with a large range of potential light intensities.

Looking at the range of options, phototransistors seem to typically have a poor ratio of dark current to light current, but tend to be cheaper.

Photodiodes seem to have a better ratio of dark/light currents and are fast, but the parts are MUCH more expensive.

Are there any tricks to getting the wide dynamic range I seek? As cheap as possible?

 

Hello,

Perhaps the following PDF might give you some ideas:
http://educypedia.karadimov.info/library/Sharp photodevices.pdf

This is a link from this page of the EDUCYPEDIA:
http://educypedia.karadimov.info/electronics/composemiconductors.htm#Phototransistor_technology

There is also a seperate page for the photo diodes:
http://educypedia.karadimov.info/electronics/composemiconductorsphoto.htm

Bertus

 

Hello,

Perhaps the following PDF might give you some ideas:
http://educypedia.karadimov.info/library/Sharp photodevices.pdf

This is a link from this page of the EDUCYPEDIA:
http://educypedia.karadimov.info/electronics/composemiconductors.htm#Phototransistor_technology

There is also a seperate page for the photo diodes:
http://educypedia.karadimov.info/electronics/composemiconductorsphoto.htm

Bertus

Thank you Bertus.

 

I am working on a product requiring a photo sensor to detect white light, I need the largest possible dynamic range (1000:1 light levels) at the minimum cost.

Response time: 200 us rise/fall
Photo-conductive operation- (needs to sink current in proportion to light levels)
Long term / temp stability not required, device will autocal for every measurement.
No need for good linearity, I am not building a measuring device, just a lights on/off detector, with a large range of potential light intensities.

Looking at the range of options, phototransistors seem to typically have a poor ratio of dark current to light current, but tend to be cheaper.

Photodiodes seem to have a better ratio of dark/light currents and are fast, but the parts are MUCH more expensive.

Are there any tricks to getting the wide dynamic range I seek? As cheap as possible?

BPW34 is not that expensive

 

I am working on a product requiring a photo sensor to detect white light, I need the largest possible dynamic range (1000:1 light levels) at the minimum cost.

Response time: 200 us rise/fall
Photo-conductive operation- (needs to sink current in proportion to light levels)
Long term / temp stability not required, device will autocal for every measurement.
No need for good linearity, I am not building a measuring device, just a lights on/off detector, with a large range of potential light intensities.

Looking at the range of options, phototransistors seem to typically have a poor ratio of dark current to light current, but tend to be cheaper.

Photodiodes seem to have a better ratio of dark/light currents and are fast, but the parts are MUCH more expensive.

Are there any tricks to getting the wide dynamic range I seek? As cheap as possible?

Photodiodes (can be) very fast but are not too sensitive - Phototransistors have gain which makes them more sensitive, but they're slower.

Cd-S LDRs are the easiest to interface, and are the closest match to the human eye response curve - but they're *REALLY* slow, and I'm not too sure about RoHS compliance (Cadmium is *VERY* toxic!).

 

Thanks all for your feedback, I will be experimenting with a bunch of sample parts, both photodiodes and transistors.
I have a feeling the photodiode is going to be the winner.

 

You don't state the light levels, but even so you should be able to develop a signal from 10 mv to 10 volts with a photo diode easily enough.