Photo-Transistor Circuit

Thread Starter

tritechinc

Joined Dec 21, 2015
4
Has anyone ever seen a circuit like this before? The emitter is tied to VCC.

Please note that the diode is a photo-diode, there is an emitter circuit but it is not shown. I am trying to copy a small circuit board from a defective IR receiver. There are no schematics and the company is long gone. I traced out the circuit paths and diode checked the transistor. I do not know the resistor value because that is what failed, I should be able to figure that out doing a little math. (The top blew off so I can not read the code, the entire thing is smt and on a board 2cm x 2cm.)

Can anyone help me?
 

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Thread Starter

tritechinc

Joined Dec 21, 2015
4
Red is VCC (+12vdc), Blk is GND and YEL is the circuit output of which has +12vdc on it. When the circuit operates it should pull YEL to ground. I don't understand why the emitter is tied to VCC, then goes through that resistor to the transistor base. I want to know if this circuit would actually work, if not then I have something wrong. (But I don't think I do)
 

hp1729

Joined Nov 23, 2015
2,304
Has anyone ever seen a circuit like this before? The emitter is tied to VCC.

Please note that the diode is a photo-diode, there is an emitter circuit but it is not shown. I am trying to copy a small circuit board from a defective IR receiver. There are no schematics and the company is long gone. I traced out the circuit paths and diode checked the transistor. I do not know the resistor value because that is what failed, I should be able to figure that out doing a little math. (The top blew off so I can not read the code, the entire thing is smt and on a board 2cm x 2cm.)

Can anyone help me?
Wow! given those three parts the most likely configuration (figure G) is the farthest from your findings. :)
 

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hp1729

Joined Nov 23, 2015
2,304
There is no the right opto transistor, so I can't analyze further, the circuit could be like as the right one.

View attachment 96989
Have you considered just putting a voltage on it and see what it does? +5 V to red, ground to back. Tie a pullup resistor from yellow to +V. Shine a light on the sensor (IR TV remote?) and see if the output goes low.
 
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