Phototransistor with 2 terminals and a transparent cap as the 3rd one

[A.Anand Srinivasan]

i've heard that a photo transistor has 2 terminals and the transparent cap acts as the 3RD TERMINAL(base)... of late i bought a phototransistor L14G3 which has 3 terminals and when i checked its datasheet it is given as an hermetic silicon phototransistor and the datasheet also shows 3 terminals....

I JUST WANTED TO KNOW WHETHER MY VIEW OF THE PHOTOTRANSISTOR IS RIGHT OR NOT....

 

[Pld4me]

Re: phototransistor

The PT you have chosen has a connection to the base for a resistor. Access to
the base allows a base-emitter resistor to be connected. A high RBE value will prevent low levels of light from triggering the phototransistor and help provide a more digital output.

 

[nguyennam]

Re: phototransistor

Some phototransistors have only 2 pins: C and E, and they are very similar in shape to photodiode, beware of this.
Some have all of 3 pins, B, C and E.
Most of phototransistors are npn (or more exactly I have never seen any pnp phototransistor).

For the 2-pin PT, base current occurs from light stimulation, more light more base current, you cannot access base circuit.

For the 3-pin PT, of course base current still occurs from light stimulation, but the base pin gives you more actively access base circuit and base current, so you can more easily modify the circuit according to your needs.

nguyennam

 

[asas]

Re: phototransistor

I agree entirely with nguyennam!!

 

[mianfraz]

Re: phototransistor

its almost right, visit howstuffworks.com to make it more clear...see ya there