is this a pnp or npn photo transistor (qre1113)

Thread Starter

dolomite dave

Joined Aug 13, 2009
6
Hi,

i am looking to use a Fairchild QRE1113gr but i cant figure out what type of photo transistor it is. let me explain my confusion, the data sheet shows this


pin 3 being the collector and pin 4 being the emitter. surly this makes this a pnp arrangement, but when i have searched google for this part every application i find shows this part as an npn type like this.

so is it an npn or pnp type? what could i look for in the datasheet to help me know which one it is. i must admit i am more inclined to think it is a npn and due to the fact that people are using this device in this way.

thanks
Dave
 

Denesius

Joined Feb 5, 2014
101
I agree, the Fairchild datasheet is confusing. But, the difference in the maximum rating between the Vceo (30V) and the Veco (5V), is a good way to tell which way the C-E junction is setup. It is the equivalent of a NPN
 

GopherT

Joined Nov 23, 2012
8,012
It's optoisolator, transistor is npn.
It is a reflective proximity sensor, not an opto-isolator.

@dolomite dave
I have never seen a PNP phototransistor, I don't believe they exist and I see no point in making one, I couldn't imagine how it would work. Phototransistors are NPN.

The pins are clearly labelled in the datasheet.

These sensors work very well. We used them on a mini sumo bot last year.
 

cmartinez

Joined Jan 17, 2007
6,971
Hi,

i am looking to use a Fairchild QRE1113gr but i cant figure out what type of photo transistor it is. let me explain my confusion, the data sheet shows this


pin 3 being the collector and pin 4 being the emitter. surly this makes this a pnp arrangement, but when i have searched google for this part every application i find shows this part as an npn type like this.

so is it an npn or pnp type? what could i look for in the datasheet to help me know which one it is. i must admit i am more inclined to think it is a npn and due to the fact that people are using this device in this way.

thanks
Dave
Easy rule of thumb: When looking at any transistor's graphic, when it's NPN, it's arrow Never Points In... and when it's PNP, it's arrow Points iN Permanently.
 

GopherT

Joined Nov 23, 2012
8,012
Easy rule of thumb: When looking at any transistor's graphic, when it's NPN, it's arrow Never Points In... and when it's PNP, it's arrow Points iN Permanently.
Unfortunately, the datasheet had no arrows. Maybe the gap on the emitter was a image-processing error that should have been an arrow.

image.jpg
 

ScottWang

Joined Aug 23, 2012
6,898
It's easy to identify that it is an npn phototransistor, the normal b of npn bjt is the current flows through from outside into b to e, but the b of pnp bjt is the current flows through from e to b to outside.

The diagram shown that the phototransistor receive the reflection light from outside and converts the light energe to current flows through b to e, so that is an npn phototransistor, I can't imagine that how a pnp phototransistor going to works like that.
 
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