phototransistor

Thread Starter

hazim

Joined Jan 3, 2008
419
Hi all
I have some phototransistors that I need to use in my senior project. The problem is as it seems, I am not using these phototransistors correctly or something else is going wrong... as you can see in the attachment, it have only two pins; as I know, they are the emitter and the collector. Which is the emitter and which is the collector? I have tried to use it in both directions and it didnot worked with me...... I need your help please as soon as possible...
awaiting your reply..
Thanks
 

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bertus

Joined Apr 5, 2008
19,934

beenthere

Joined Apr 20, 2004
15,808
The tab marks the emitter.

Put the emitter to ground and pull the collector up to Vcc with about 47K - 100K. Phototransistors don't have much power.
 

Thread Starter

hazim

Joined Jan 3, 2008
419
I don't know what type it is bertus, but I attached a picture of it... beenthere I tried what you said but it didn't worked... I put in face to it an assured IR LED.. this didn't affect the resistor's voltage even by 1mV!

I want to use it as an IR receiver...
 

radiohead

Joined May 28, 2009
505
see the little tab on the case of the transistor? That's the emitter. The other pin is the collector. The base is the light receptor. They are typically used to detect infrared light (but can detect laser light) like when you use your remote (IR transmitter) on your DVD player (IR receiver). You might find what you need here: http://www.discovercircuits.com/I/infrared.htm
 

bertus

Joined Apr 5, 2008
19,934
Hello,

Do you have a schematic from what you have upto now?

As you say it could also be an IR led.
If it is an IR led you could measure the diode with a multimeter.(diode test).
This can also be used as sensor , but it will be less sensitive.

Greetings,
Bertus
 

ELECTRONERD

Joined May 26, 2009
1,146
If you have an oscilloscope, a sine wave generator, you could produce a sine wave and put the transistor opon the input of your scope. If its an IR LED, it will cut the negative portion (or positive if you reverse it) off. If it doesn't, then it must be a transistor.
 

Thread Starter

hazim

Joined Jan 3, 2008
419
yes I connected it right.... it gives me good condition while testing it by multimeter(diode test).... anyway I just tried these basic circuits with the phototransistor (attached) and they are not working.. I'm now convinced that the phototransistors I bought are broken!!
 

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Thread Starter

hazim

Joined Jan 3, 2008
419
it's not working neither as a phototransistor nor as a IR LED!!
 

radiohead

Joined May 28, 2009
505
the phototransistor is only a detector, there will be negligible signal present. Hence, the signal must be amplified to a useful level. Try feeding it into an op amp to boost the signal.
 

Thread Starter

hazim

Joined Jan 3, 2008
419
see the attached picture in post 8, for experimenting it I used an IR LED (emitter) but there was no change in Vo...
 

radiohead

Joined May 28, 2009
505
with that circuit, there won't be. Connect a multimeter set to measure ohms across the emitter and collector. When light is applied to the base, the resistance should drop.
 

Audioguru

Joined Dec 20, 2007
11,251
Since you used the "diode test" on your multimeter to test the "photo-transistor" and it conducted then it must be a photo-diode that has an extremely low output signal.
 

THE_RB

Joined Feb 11, 2008
5,430
I'm with Audioguru, if it tested as a diode junction it is probably a photodiode, so try connecting it REVERSED with a 47k resistor.
 
it's not working neither as a phototransistor nor as a IR LED!!
Hazim, the reason why your phototransistor doesn't work is probably because some nut hooked it up backwards! No, seriously, I have worked with infrared photo-transistors before, and they can be a lot of fun. In my own case, I was resolving a noise problem which turned out to be caused by an unshielded transformer.
 

hwy101

Joined May 23, 2009
91
I have a Shooting Chrony circuit board here that someone shot right thru the LCD display, it's pretty much toast.
It uses that same IR detector hazim is talking about.
Just had a quick look at this board it reveals the collector of this photodiode is fed to a gate of a J177 (P-channel FET) and the (source) of the FET is connected to pin 7 of an LM324, so a bit of amplification is required.
 

Thread Starter

hazim

Joined Jan 3, 2008
419
it will never work....
here is an IR receiver LED... I'm using it.. it's perfect
 

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hwy101

Joined May 23, 2009
91
It's been so long since I used one of those I totally forgot, yes they do work well for simple projects, it's a Radio Shack Part # 276-145
 

radiohead

Joined May 28, 2009
505
Radio Sh*t. I dismiss them as a cell phone store!!! They barely sell components anymore. As for IR circuits, there are thousands of them on line if you do a google search for "IR circuit schematics." Hazim, foot a dollar and buy a new IR diode and maybe another buck for an IR receiving transistor...most places will sell them as a pair. Take your circut from there....
 
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