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PHOTO DIODE HELP

 
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ramses_II
HG Junior


Joined: 21 Sep 2006
Posts: 10

PostPosted: Tue Oct 10, 2006 1:26 pm    Post subject: PHOTO DIODE HELP Reply with quote

I have a question about photo diode

HOw does it work in a circuit??

It allows a current to flow when there is no light, and doesn't allow current to flow when there is light.....or reverse

this is the picture how I think it works:




The LED should turn on when there is no light and it should turn off when there is light......IS this true or not?

PLZ HELP!!!!!!!!!!!!!!!
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Modio
HG Contributor


Joined: 23 Apr 2006
Posts: 29

PostPosted: Tue Oct 10, 2006 8:09 pm    Post subject: Reply with quote

the photodiode works by turning on the light when there is none

and might i suggest a course in electronics? i took one and it really helped me out


Last edited by Modio on Tue Oct 10, 2006 8:21 pm; edited 1 time in total
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Tue Oct 10, 2006 8:13 pm    Post subject: Re: PHOTO DIODE HELP Reply with quote

ramses_II wrote:
I have a question about photo diode

HOw does it work in a circuit??

It allows a current to flow when there is no light, and doesn't allow current to flow when there is light.....or reverse

this is the picture how I think it works:




The LED should turn on when there is no light and it should turn off when there is light......IS this true or not?

PLZ HELP!!!!!!!!!!!!!!!


Hi Ramses,

That is how most of them work (high resistance in the dark). However look up the specs. of the device. Just like a photo-cell the amount of current that they can pass is generally very small. It is probably not enough to light an LED. There are lots of different versions though so you might find one that can pass enough current and directly drive the LED.

The result may not be what you want though since bright light it would cause the device to conduct and light the LED (if it could pass enough current).
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Tue Oct 10, 2006 8:16 pm    Post subject: Reply with quote

Here is a great page with some more info:
http://en.wikipedia.org/wiki/Photodiode
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ramses_II
HG Junior


Joined: 21 Sep 2006
Posts: 10

PostPosted: Wed Oct 11, 2006 4:41 am    Post subject: Reply with quote

Yeah i know that it should let small current flow but I was just wondering how does it work, i would of put a transistor between so the photodiode can turn on the led......

BTW- i have a 1 question more:

I have a phototransistor "tsop 1138" and I'm just wondering how does the phototransistor work???

And why does it have 3 legs???

PLZ HELP

and a circuit with explanation would really help!
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Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Wed Oct 11, 2006 7:17 am    Post subject: Reply with quote

ramses_II wrote:
Yeah i know that it should let small current flow but I was just wondering how does it work, i would of put a transistor between so the photodiode can turn on the led......

BTW- i have a 1 question more:

I have a phototransistor "tsop 1138" and I'm just wondering how does the phototransistor work???

And why does it have 3 legs???

PLZ HELP

and a circuit with explanation would really help!


That device contains a photo diode PLUS lots of other goodies...
http://www.vishay.com/docs/82006/82006.pdf

Have a look at the block diagram, the photo diode is the left most item in the picture (the diode with squiggles going to it). The pins on the left of the block diagram are marked. In this case the three pins are
* Operating Voltage
* Ground
* Output Signal
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Wed Oct 11, 2006 7:24 am    Post subject: Reply with quote

This device represents a typical photodiode

http://www.silonex.com/datasheets/specs/103193.htm

Note the low current (micro amps)
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ramses_II
HG Junior


Joined: 21 Sep 2006
Posts: 10

PostPosted: Thu Oct 12, 2006 12:55 am    Post subject: Reply with quote

IF I want to use it as a photo diode for Infrared light i just
connect the suplly to the pin 2 and the output is pin 3?

So when it detects infrared light it will let current flow from pin 2 to pin 3?
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