What this circuit does?

[leonel]

NOR??

Just one more transistors question...
For example in the picture shown if A=1 and B=0, the collector of the A transistor is in low state and the collector of the B transistor is in the high state! We have the same net with two different states!!!!???
How does it turns a nor?
Regards!

 

[audioguru]

Hi Leonel,
There is no conflict because each transistor has no positive power supply of its own. The collector resistor R27 pulls the output high when both transistors are turned off.
This is called "wired-or logic" and cannot be done with ordinary logic inverters or gates because they actively pull their outputs both low and high. Their outputs would fight each other if they were connected together like this and one output is high and the other output is low. :lol:

 

[leonel]

who wins

And who wins if one output his high and the other one low? :?:

 

[audioguru]

With ordinary inverters or gates that have active high and low outputs, if their outputs are connected together and have different logic states, the winner is the one that doesn't smoke much. Both might be destroyed and destroy the power supply too! :shock:

 

[leonel]

?

I don´t understand but i agree with you :?

 

[ljcox]

Re: NOR??

Just one more transistors question...
For example in the picture shown if A=1 and B=0, the collector of the A transistor is in low state and the collector of the B transistor is in the high state! We have the same net with two different states!!!!???
How does it turns a nor?
Regards!

Transistors do not have "high" or "low" states.

They are either off, in their active region or saturated (on).

If A = 1 and B = 0, transistor A is on and B is off.

Consider the transistor in your circuit as though they are switches.

Len

 

[leonel]

Thank you

Sometimes it´s just one word that we realize the meaning of one thing... and the word is switch.
So we can say that the image shown it´s an RS flip flop. That´s right?
Thank you to all of you that helped me

 

[audioguru]

That's correct!
The 4 transistors and 10 resistors make an RS flip-flop circuit about the same as half of a cheap CD4001, except the CD4001 doesn't draw any supply current and switches much quicker. :lol: