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Best way to amplify the signal generated from a phototransistor?

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biomedhed

New Member
If i direct a laser beam through a piece of a certain material of differing density onto a phototranistor, what would be the best way to amplify this signal?

i.e. through an op amp, or through a couple of transistors?

The output will be fed into a computer via "powerlab" and therefore needs to be in the range of 1mv to 1V.

Any help would be much appreciated.
 

Chippie

Member
Couple of things spring to mind...

What phototransistor?

What voltage are you running it from...

With the voltage range you spec...you are looking at something that has a gain of around 1000...Op amp looks favourable...You may need to stage the gain...
 

biomedhed

New Member
Couple of things spring to mind...

What phototransistor?

What voltage are you running it from...

With the voltage range you spec...you are looking at something that has a gain of around 1000...Op amp looks favourable...You may need to stage the gain...
Phototransistor is this > SFH300-3 Phototransistor > Maplin

The unit when finished will be ran from a 9 - 15V regulated supply depending on what's available in the lab.

SO would a simple non inverted op amp circuit do the job?

Cheers
 

Chippie

Member
I dont think you will achieve a gain of 1000 from a single op amp...you may need to string a few together...
 

audioguru

Well-Known Member
Most Helpful Member
An ordinary opamp has a gain of about 200,000 from dc to about 5Hz. Negative feedback can be added to reduce the gain and increase the cutoff frewquency.

Or additional opamp amplifier circuits can be used for a higher cutoff frequency with more gain.
 

Chippie

Member
An ordinary opamp has a gain of about 200,000 from dc to about 5Hz. Negative feedback can be added to reduce the gain and increase the cutoff frewquency.

Or additional opamp amplifier circuits can be used for a higher cutoff frequency with more gain.

Think my figure must but a bit off...damn keyboard!! or the extra zero's got lost in the post....

I'd expect to see a number of op amps with feedback loops to keep them from oscillating....
 

biomedhed

New Member
Think my figure must but a bit off...damn keyboard!! or the extra zero's got lost in the post....

I'd expect to see a number of op amps with feedback loops to keep them from oscillating....

Any chance of providing me with a circuit diagram?
 

audioguru

Well-Known Member
Most Helpful Member
Think my figure must but a bit off...damn keyboard!! or the extra zero's got lost in the post....

I'd expect to see a number of op amps with feedback loops to keep them from oscillating....
An opamp only oscillates when it is built on a horrible breadboard with wires all over the place. On a properly designed pcb or Veroboard it works perfectly.
 
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