Nand circuit, placement of resistor.

Thread Starter

gilleslag

Joined Dec 23, 2020
14
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.

nand circuit_LI.jpg
 

Thread Starter

gilleslag

Joined Dec 23, 2020
14
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 :D
 

jpanhalt

Joined Jan 18, 2008
10,933
If you redraw the circuit with that resistor moved, you get:

1608722241712.png

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.
 

ericgibbs

Joined Jan 29, 2010
11,577
hi,
You could put that Green LED in series with the collector resistor, say a 330R
E

Update:
Added image.
AAA 920 12.00.gif
 
Last edited:
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