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LEDs as detectors for UV and IR. What amplifier to use?

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neazoi

neazoi

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Hello, I have found from experiment that most LEDs, including UV and IR, can be used in reverse to detect the range of frequencies they are designed to emit.

I would like to make a simple detector using a transistor amplifier to drive a meter. Can I use one of these FET static detectors amplifiers and connect the LED cathode to the Gate instead?
 

neazoi said:
Hello, I have found from experiment that most LEDs, including UV and IR, can be used in reverse to detect the range of frequencies they are designed to emit.

I would like to make a simple detector using a transistor amplifier to drive a meter. Can I use one of these FET static detectors amplifiers and connect the LED cathode to the Gate instead?
Click to expand...
I think an LED would act like a tiny solar cell like a photo-diode when it has no reverse bias. If the source of the FET is grounded then light on the LED would turn off a Jfet. But it probably would not produce enough voltage to change the jfet conduction much.

If the LED had a reverse bias voltage (maximum only 5V) then light on it would increase its leakage current like a photo-diode. It might be able to turn on a Mosfet.
 
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    neazoi

    neazoi

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Audioguru said:
I think an LED would act like a tiny solar cell like a photo-diode when it has no reverse bias. If the source of the FET is grounded then light on the LED would turn off a Jfet. But it probably would not produce enough voltage to change the jfet conduction much.

If the LED had a reverse bias voltage (maximum only 5V) then light on it would increase its leakage current like a photo-diode. It might be able to turn on a Mosfet.
Click to expand...

So how you propose to connect the LED to the jfet? Maybe if I connect the led from the drain to the gate, with the cathode connected to the gate?
using a depletion mode jfet could be better?
 
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