Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need help designing an SCC circuit

Status
Not open for further replies.

mif987

New Member
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
 
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"????
 
Last edited:
I thought SCC was the acronym for signal conditioning circuit... :p 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
 

Attachments

  • Photo Trans.gif
    Photo Trans.gif
    6 KB · Views: 331
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.
 

Attachments

  • Diagram.jpg
    Diagram.jpg
    16.2 KB · Views: 214
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?
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top