What this circuit does?

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leonel

New Member

• Jun 16, 2005

• #21

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

Well-Known Member

Most Helpful Member

• Jun 16, 2005

• #22

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:

 

L

leonel

New Member

• Jun 16, 2005

• #23

who wins

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

 

audioguru

Well-Known Member

Most Helpful Member

• Jun 16, 2005

• #24

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:

 

L

leonel

New Member

• Jun 16, 2005

• #25

?

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

 

L

ljcox

Well-Known Member

• Jun 16, 2005

• #26

Re: NOR??

leonel said:

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!

Click to expand...

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

 

L

leonel

New Member

• Jun 17, 2005

• #27

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

 

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audioguru

Well-Known Member

Most Helpful Member

• Jun 17, 2005

• #28

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: