Basic IR circuit

[joseche]

Hi there,
I am trying to use the radio shack IR detector 276-0142.
It says:
Vce = 70v
Vec = 5v
Ic = 50mA
Spectral bw: 620-980nm

So what I did is to put a voltaje source of 9v, then a 115Ω, then the detector, then a led, then ground. This means that when the detector is totally ON it will let a current of (9-1.2)/115 = 67mA

Means that if the detector were completely closed the led will be toasted (receiving 67mA) but I am not beaming it strong enough.

Is this idea ok ?, how can I know what to expect if the emitter on that same package says it transmits 950nm ?, this means that if I put the emitter right next to the detector the led should receive the 67mA ?, why is the Vce so high ?

Sorry if these questions sound silly, I am just a wannabe in the EE field.

Thanks

 

[ericgibbs]

hi j,
The Vce, Vec, Ic are absolute maximum ratings for the devices.

For the photo-detector use a series resistor, in the collector of the detector, with the LED to limit the current to approx 15mA.

For the emitter diode use a series resistor to limit the current to approx 20mA.

EDIT:
Look at and run this asc Sim
If you dont have the opto coupler model, let me know.

 

[joseche]

the detector is always on .... why ?????

I turned off the lights in the room and everything and it is always on, in fact I checked putting emitter and it lights on with both so the problem is not that I am using the wrong item...

What can it be ?

 

[ericgibbs]

the detector is always on .... why ?????

I turned off the lights in the room and everything and it is always on, in fact I checked putting emitter and it lights on with both so the problem is not that I am using the wrong item...

What can it be ?

hi j,
Please post a circuit showing how the photo transistor is connected.

Did you run my simulation asc file.???

 

[audioguru]

The detector had too much current so now it is shorted and it appears to be turned on all the time.

 

[joseche]

I have exactly what you have on the right side of your circuit,

9v - 470ohms - led - detector - ground

and the led is always on, is it possible that the long leg of the detector is the cathode ?

 

[audioguru]

When you use parts from RadioShack then you don't know the manufacturer's name, you don't get a detailed datasheet and they charge much more than a real part from a real electronics parts distributor.

They say it is a photo-transistor, not a photo-diode but maybe they are wrong.
A photo-transistor connected backwards will not conduct all the time but a photo-diode will.

 

[joseche]

hey audioguru, seems like you hit it, I found this on radioshack's website:

Comments about RadioShack Matched Infrared Emitter and Phototransistor Detector:

This package has been misnamed. The phototransistor is actually a photodiode. I tested this with a multimeter. resistance changed based on how far away an abject was. I then tested it in a an led circuit. The led's brightness was determined on how far away the object was. However if you need a photodiode application this is perfect.

So, seems like #1 it is a photodiode, and #2 the legs are wrong, longest should be on the ground side. I will try when I get home today.

Thanks