Author Topic: Photo Diode, or Photo Transistor?  (Read 2670 times)

0 Members and 1 Guest are viewing this topic.

Offline TheKraken

  • Contributor
  • Posts: 8
Photo Diode, or Photo Transistor?
« on: July 11, 2013, 04:07:44 am »
I have not quite been able to figure out what it is that I would need specifically, to switch on a circuit ( with High Voltage) using an IR LED, or even a normal LED when its path is blocked ( low to no light ) to a sensor. And I quite honestly am not sure what type of sensor I should really look for. A photo-diode, or possibly a photo-transistor? It seems that the diodes that can handle upwards of 300vdc are far out of the price range for me, So i was thinking perhaps a photo-transistor would work better, although most of these things are trigger on light, instead of triggering on no light ( IR light is block, or maybe even use a small laser and laser sensor? ). The ability of the circuit to switch on extremely fast is important, and I need it to be built in a certain fashion that allows the use of the HV circuit becoming complete. Basically, the light path will be blocked, and in short order I need a HV circuit to activate in response. Voltages up to around 1kv will be used in the activated circuit, the path 'trip switch' does not need to be powered on the same circuit if that makes things easier.
 

Offline IanB

  • Super Contributor
  • ***
  • Posts: 9668
  • Country: us
Re: Photo Diode, or Photo Transistor?
« Reply #1 on: July 11, 2013, 04:29:17 am »
It seems that the diodes that can handle upwards of 300vdc are far out of the price range for me,

The photo sensing element does not also have to be the switching element. Your design job will be much easier if you consider your circuit to be composed of two logical elements: a light detection element and a switching element. If you design this way you isolate one or the other to make testing easier. Furthermore you could swap out one switching element for another or one sensing element for another to get more options.

i was thinking perhaps a photo-transistor would work better, although most of these things are trigger on light, instead of triggering on no light

Of course. Transistors are switched on by current or voltage at the base and incident light energy does the same job. But there is nothing to stop you using another circuit element to invert the signal...
I'm not an EE--what am I doing here?
 

Offline TheKraken

  • Contributor
  • Posts: 8
Re: Photo Diode, or Photo Transistor?
« Reply #2 on: July 11, 2013, 04:48:33 am »
I was thinking about potentially using a 'Photo interupter' I had not found one previously for the sensing distance needed. I have a little 5mm slot type 'opto coupler' but need something more along the lines of 15-20mm for the application. I did find a few recently on digikey,  There seem to be two types, logic output and transistor type, and im not quite sure which would be the best option. budget minded and simplicity of the switching function would be key.
 

Offline IanB

  • Super Contributor
  • ***
  • Posts: 9668
  • Country: us
Re: Photo Diode, or Photo Transistor?
« Reply #3 on: July 11, 2013, 04:59:07 am »
IR remotes work from the other side of a room, so distance is not an intrinsic problem for a photodetector circuit.

If there is ambient light in the surroundings you can modulate your source with a suitable frequency so you can filter out ambient light interference.

To detect the object in the light path you can use a sensing circuit that looks for sudden changes in intensity of the receiving signal.
I'm not an EE--what am I doing here?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf