# Nand circuit, placement of resistor.

#### 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.

#### ericgibbs

Joined Jan 29, 2010
11,577
Hi gill,
Welcome to AAC,
What is the A and B voltage.?
E

#### 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

#### Ian0

Joined Aug 7, 2020
1,120
If you move R1, is there still a connection to +6V. If so, where does it go?

#### ericgibbs

Joined Jan 29, 2010
11,577
hi gill,
Are you sure you have transistors connected correctly?
E

A clear photo of the layout would help.

#### gilleslag

Joined Dec 23, 2020
14
Hi Eric,

Transistors are correctly connected. I double checked it.

#### jpanhalt

Joined Jan 18, 2008
10,933
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.

#### ericgibbs

Joined Jan 29, 2010
11,577
hi gill.
It should work as expected.
LTSpice simulation.
E

#### Attachments

• 28.8 KB Views: 11

#### gilleslag

Joined Dec 23, 2020
14
Here is a picture of my circuit if that helps.

#### ericgibbs

Joined Jan 29, 2010
11,577
hi gill,
Is it connected as shown in post #7.?
Collector directly to 9v
E

#### gilleslag

Joined Dec 23, 2020
14
hi gill,
Is it connected as shown in post #7.?
Collector directly to 9v
E
yes

#### ericgibbs

Joined Jan 29, 2010
11,577
hi,
Bad idea, you may have damaged the transistors.
E

#### gilleslag

Joined Dec 23, 2020
14
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?

#### ericgibbs

Joined Jan 29, 2010
11,577
hi,
Rebuild with resistor between collector and 9v and retest, if it works they are OK,
E

#### gilleslag

Joined Dec 23, 2020
14
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.

#### ericgibbs

Joined Jan 29, 2010
11,577
hi,
What do you plan to do with NAND Gate.?
E

#### gilleslag

Joined Dec 23, 2020
14

#### 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:

Last edited: