Photodiode current to voltage converter HELP

hgmjr

Joined Jan 28, 2005
9,029
Here is the Application Note available on National Semiconductor's website that describes the circuit you have posted.

Figure 3 in this application note is basically the same circuit you are asking about.

hgmjr
 

Thread Starter

dickcruz

Joined Jan 7, 2007
20
Yeah, I am aware of that. I infact got the picture extracted out of there. I still need to know how the circuit works.
I also want to know whether i can use a LM741 as an op amp in stead of the one shown ; and use a SLSD71N2 as the photdiode.

I have also considered looking at the LED photometer by forrest M. but i've had moderate success in making the instrument vary output with light. How exactly does the LED act as a detctor? Any thing i should know?

Thanks
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

The photometer circuit is AC only. Look at how the components respond to the photodiode's change in conduction.

741 op amps are pretty useless animals any more. Use an op amp with a much higher input resistance and lower leakage.
 

Thread Starter

dickcruz

Joined Jan 7, 2007
20
Hi,
So i can't use a stepdown trans. with a rectifier to get a 5vdc?
What can i substitute for the op-amp??
and
Could someone please tell me how the circuit works?

Thanks
 

Distort10n

Joined Dec 25, 2006
429
What exactly do you not understand about the circuit? National's application note covers the basics well enough.

Looks to me that you can use this figure in pulsing type of applications obviously centered around 2.5V. It is also rather bulky if you are just going to use a voltage feedback amplifier.
I understand why they have the transistor there to isolate the photodiode capactiance from the summing junction, but it seems extraneous.
Use a blocking cap in series with the output and then rectify it.

What are you planning to do with your rectified voltage?
 

Thread Starter

dickcruz

Joined Jan 7, 2007
20
Ok that's what i needed i dint know what the transistor was doing there and it got me in a fix.
I just plan to connect it to a volt meter to calculate the voltage.

But im still not able to find a substitute for the op-amp it seems that the one in the schem. is deprecated.

Ill need this to be able to complete the circuit.

This is one of my first few circuits so it was hard to shift from theory to practical so would it be ok i uploaded a picture of the stripboard i soldered?

Thanks Guys
 

beenthere

Joined Apr 20, 2004
15,819
For that matter, an outfit called TAOS makes packaged light-to-voltage converters. They come in TO-92 packages for just about $1.25. Mouser carries them. Sensitivity goes from about 1050 nm to 240 nm. Hard to beat.
 
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