Phototransistor; 5mm;? Stock : Minimum : 5 Multiples : 1. Manufacturer : Everlight. Category : Phototransistors. Description : Phototransistors Phototransistor.

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May Posted by Dimitar Kovachev. IR LED and a photo-transistor - which is which? All was fine, until the salesman at the local shop told me:. Probably someone has misplaced them, when restocking. Anyway, I purchased them. It was time to do some tests and measurements. LEDs and photo-transistors can be wired in a similar way — using a current-limiting resistor in series. Under certain conditions, they will conduct electricity. When forward-biased, the current through the photo-transistor is proportional to the amount of light.

This leads us to our criteria — the current through a forward-biased LED is a constant; the current through a forward-biased PT varies with light. To drive the LED, it has to be above 1. The final step was to take a digital multi-meter DMM , set it to current measurement, 20mA range and complete the circuit:. It was a photo-transistor. Bookmark the permalink.

Not sure if your confusion about which component is which got resolved. I bought today. The LED is blue, the phototransistor is clear. You have 2 LEDs in your picture. Chanced upon this post, and while the proper testing of the components to electrically differentiate the two is useful knowledge, but thought it worth mentioning: if you have a device you expect is an IR led, you can use a digital camera such as on a typical cellphone and see the IR emission, as typical CCDs are sensitive to that wavelength.

This is a useful way to verify that an IR remote control is in fact transmitting. Thanks for writing this up! Photo diodes have always confused me a bit. Use your smart phone or camera. The image sensors pick up IR! Yes it did checked with a camera. Both pt and led as with photodiodes are composed of pn junctions and should theoretically light up when forward biased to greater than their turn-on voltage.

Not really Ike. They work differently. When a LED is forward biased, it emits light while the transistor switches and amplifies the colector-emitter current if the base-emitter junction is forward biased.

So a LED will light and a phototransistor will not. The devices you present here do not appear to have that characteristic. Note that a reverse biased LED can conduct when light of a suitable wavelength is presented generally centered around the wavelength which that LED emits when normally driven. This can be useful for driving a darlington or as input to an opamp or inamp.

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Mostly harmless… Exploring electronics, programming and photography. Home About. A LED or a phototransistor?! Share this: Twitter Facebook. Like this: Like Loading Leave a comment Comments Tony Roberts January 6, at Dimitar Kovachev January 6, at Sean Straw July 8, at Kenneth Olsen January 4, at Dimitar Kovachev February 2, at Petes March 2, at How would you go around this issue but with a phototransistor and a photodiode? Sean Straw May 12, at Leave a Reply Cancel reply Enter your comment here Fill in your details below or click an icon to log in:.

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Low voltage. Mostly harmless…


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