Phototransistor with Base Pin ! why !!

[ahmed osama]

3 pin phototransistor

Dear ALL

now i saw a lot of datasheet for "Phototransistor with Base Pin (3 pins)" and all are putting a small test circuit without the base pin connected !!

i need to know what the base pin do and how to use it??

and what is the diff. between

"Phototransistor with Base Pin (3 pins)"
"Phototransistor without Base Pin (2 pins)"
"Photodiode (2 pins)"

thanks

 

[FvM]

phototransistor 3 pin

With the 3-pin phototransistor (most traditional metal can packages and some optocouplers have it) you can:
- connect CB as a photodiode
- ignore the base connection (most applications)
- design a special circuit, that makes use of the base terminal, e.g. connect a schottky diode for faster switching operation