can someone help me with this circuit....???

[jawadali477]

hi,
can any one help to make me understand how this circuit is working? i mean circuit analysis.

thanks

jawad

 

[leo_o2]

It seems it is used to detect light brightness change. Capacitor will pass AC signal and block DC signal.

 

[LvW]

hi,
can any one help to make me understand how this circuit is working? i mean circuit analysis.

thanks

jawad

It is a classical arrangement of three amplifier stages in series. If you know how a transistor works you will also understand the principle of this circuit. The transition npn-pnp-npn is because of the dc level of the three operating points.

 

[jawadali477]

thats why i asked how transisters are working in this cct....

thanks

jawad

 

[FvM]

The transition npn-pnp-npn is because of the dc level of the three operating points.

But the AC coupling would allow three npn as well. An advantage of this circuit is in better rejection of power supply interferences (higher power supply rejection ratio PSRR).

It's a circuit, that one would demonstrate in a transistor circuits lab as bad design example due to the applied bias method, equally succeptible to PVT (process, voltage, temperature) variations. A single 1Meg resistor between collector and base gives much better performance than the voltage divider without DC feedback.

 

[LvW]

But the AC coupling would allow three npn as well. .

Ohh yes, that`s correct. (When I see such an npn-pnp connection at first always the bias point comes into my mind) .