Need help designing an SCC circuit

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mif987

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I need to design an SCC circuit using lm741 or lm941 to amplify a 2µA current from a phototransistor so that it'll work with a lm311.

Help please
 
When there's IR on the phototransistor I need a High and when the IR is interrupted I need a low.
 
I have a phototransistor a nte3034A which I'm using. The thing is that I need a CPLD to count every time the IR is interrupted. The issue is that when the phototransistor is receiving the IR its output is a high but when it's interrupted the output is near 0V but it's not detected as low, so I was told that we needed a voltage comparator. But the current emitted by the phototransistor is very low ( 2µA) and I need to increase it so the lm311 works.
 
A lousy 741 is about the last amplifier I would choose for this purpose. You need something with low-noise and low input bias current; the 741 has neither.

Go to TI.com and use their parametric search tool to pick a modern opamp.

What is an "SCC"????
 
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I thought SCC was the acronym for signal conditioning circuit... I need something to amplify the current output form the phototransistor
 
Those are two components, the Photo-transistor which you have and a resistor connected to it. You don't need any current but voltage signals to determain whether there is IR signal or not on the transistor.
 
I don't get it? This is a link to your part's data sheet. With a VCE of 10 Volts the Dark Current is about 100 nA and with a VCE of 10 Volts the Typical light current should be about 1 mA so where is this 2 uA coming from? Can you post a circuit of just how this photo transistor is configured? You should (as mentioned) have a series resistor with it. Exactly how is this configured? You should have something that resembles the attached drawing.

Next, give this link a read. Scroll down to the Photocell Circuits on the linked page. Also read about comparators.

Using a phototransistor as you are doing you should not need a comparator.

Ron
 

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Ok I'll try to explain the circuit the best I can.

The IR led has a Resistor of 470Ω. The photo transistor has a 10K resistor in the VCC input and has a IN4006JCM in its output. If I measure the current in the output it gives me 2µA.

I attached an image ( not the best diagram) of the Led and phototransistor.

My circuit needs to do the following:

When the signal between the LED and the Phototransistor is interrupted, the other component I'm using (CPLD) to do a count. SO basically everytime the signal is interrupted, the CPLD will count so I know how many times was the signal interrupted.
 

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mif987 absolutely dont need any comparators and messing with currents but only voltages! you ned to make a pull up resistor to get what you want
 
Do what Steven87 has said. Make your receiver like the drawing I posted #1 of the two and use 10 K for the collector resistor. Take your output at the collector as I drew it. The drawing you posted makes no sense and won't work.

Ron
 
Thanks to all! I'll try to put a better picture later of the circuit I'm building. By the way, anyone knows the code or number of a signal conditioning component?
 
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