Emitter joined to base?

[gtx]

Hi,


Anybody can tell me how is the function of transistor with base and emitter joined in this circuit ? Thanks

 

[Nigel Goodwin]

Anybody can tell me how is the function of transistor with base and emitter joined in this circuit ? Thanks

It's wired as a diode, and reverse biased, presumably to act as a zener?. I imagine it's a white noise generator?.

 

[mstechca]

I agree with nigel for the following reason:

the transistor that acts as a diode is an NPN. Because the base and emitter are connected together, you have effectively short-circuited one diode of the two. (remember, an NPN is two diodes with the anodes touching each other). It is reverse biased because you have the cathode of the remaining imaginary diode (or collector of NPN) connected to +ve. This is not recommended unless you use a zener diode or one which will function as a wire when the voltage is high enough. I do not recommend 1N400X diodes for this purpose.

 

[Roff]

Vcbo is 50 volts. Unless VCC is greater than 50 volts, Q806a will do absolutely nothing.