Connecting base emitter of photo transistors

[mohammad mokhtar]

Hi all
If I connect the base ( of photo transistor ) by a resistor to the emitter, and I expouse the transistor to light, wiil any current (due to light effect) will flow through
the resistor ?
How to calculate that current?
Hope the answer will not contain physics.
BR

 

[glenjoy]

Do not calculate, just connect and VOM, btw what you are doing is a feedback to have a quiscient operation of your transistor.

 

[happy2005]

Sure. Transistor base current is supplied from light source. But, some of the current will flow through resistor. Base-emitter voltage is approximately ~0.7V. So, you can calculate the current: IR=0.7/R

 

[Humber555]

If you connect a resistor between the base and the emitter of a phototransistor,
you are lowering the BE impedance, hence doing the transistor less sensitive to
the light incidence. In some cases this is a common practice to decrease the gain.


humber555