Hey everyone,

I'm new here and also a newbie who is teaching himself.
I have one question:

How come if i put resistor R1 before the output, the output is always 1? Even if A and B have an input signal.

 

Hi gill,
Welcome to AAC,
What is the A and B voltage.?
E

 

Hi,

First I will say that i used different values for the components for my circuit.
these are my values:
power supply = 9V
R1= 330ohm
R2 and R3 = 3.3kohm

A and B are also connected to the power supply of 9V.

i hope this make sense

 

If you move R1, is there still a connection to +6V. If so, where does it go?

 

hi gill,
Are you sure you have transistors connected correctly?
E

A clear photo of the layout would help.

 

Hi Eric,

Transistors are correctly connected. I double checked it.

 

If you redraw the circuit with that resistor moved, you get:



Do you see why the output is always 6V, assuming negligible current? What if you eliminate that resistor (dashed line)?

Now if you short out the supply, i.e., both transistors are saturated on, then the voltage will drop depending on how much current the 6V supply can provide.

 

hi gill.
It should work as expected.
LTSpice simulation.
E

 

Here is a picture of my circuit if that helps.

 

hi gill,
Is it connected as shown in post #7.?
Collector directly to 9v
E

 

hi gill,
Is it connected as shown in post #7.?
Collector directly to 9v
E

yes

 

hi,
Bad idea, you may have damaged the transistors.
E

 

hi,
Bad idea, you may have damaged the transistors.
E

hi,

If I put the resistor between the collector and the 9V it works just fine.
How can I test if I damaged the transistors?

 

Hello,

Have a look at this page:
https://www.petervis.com/Education/logic-gates/nand-gate-transistor-circuit.html

Bertus

 

hi,
Rebuild with resistor between collector and 9v and retest, if it works they are OK,
E

 

hi,
Rebuild with resistor between collector and 9v and retest, if it works they are OK,
E

Hi

I rebuild it and it stil works fine.

 

hi,
What do you plan to do with NAND Gate.?
E

 

hi gill,
Are you sure you have transistors connected correctly?
E

hi,
What do you plan to do with NAND Gate.?
EView attachment 225703

Hi,

Nothing.
I'm just messing arround cause I'm still learning to understand this kind of circuits.

 

hi,
You could put that Green LED in series with the collector resistor, say a 330R
E

Update:
Added image.

 

hi,
You could put that Green LED in series with the collector resistor, say a 330R
E

Now it works like an and gate