Simple non-inverting Amplifier Not working

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
I'm using the UA741 op-amp in my circuit.I'v designed the input to be of about 1 volts dc,the gain to be 11 and when testing on simulation everything went fine.However in real life the circuit didn't work as expected.It gave me a gain of 3.4 while using +/- 15 volts bais.

In the circuit i didn't have a +/- 15 volts source so instead i made a voltage divider and used a buffer circuit as to separate the ground form circut.

Notice that this is my first experience with analog ICs so please help me step by step and be patient.

Thanks in Advance...:)
 

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AlbertHall

Joined Jun 4, 2014
12,346
If pins 7 and 4 of U2 read +15V and -15V respectively then it would seen that U2 is defective.
To confirm this you could swap the two ICs. If the ±15V is now not correct then the diagnosis is confirmed.
 

AnalogKid

Joined Aug 1, 2013
11,049
If this is running only in simulation, the program might not like or understand having the 741 output "grounded" and the consequences for the following amplifier. If so, delete all GND symbols and replace them with hard connections.

Also, note that two of the 30 V return rail connection dots are in the wrong places.

ak
 
Last edited:

WBahn

Joined Mar 31, 2012
30,062
pin 2 = 0.29 v dc
pin 3 = 1.00 v dc
pin 6 = 3.29 v dc
Disconnect pin 3 and pin 6 on U2 and see what the output is when you rail the inputs (connect it to pin 7 and then pin 4). Does the output go to at least +12 V and -12 V, respectively?

Try swapping R3 and R4 so as to significantly reduce the gain and see if it works under those conditions.

One thing to be careful about, though it shouldn't be an issue in this circuit, is that U1 must be able to source/sink all of the "ground" currents in the circuit.

Can you look at the signals with an oscilloscope? It could be that the circuit is oscillating and that your meter is therefore reporting values that have little to no meaning.
 

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
If this is running only in simulation, the program might not like or understand having the 741 output "grounded" and the consequences for the following amplifier. If so, delete all GND symbols and replace them with hard connections.

Also, note that two of the 30 V return rail connection dots are in the wrong places.

ak
No it is not a simulation.On the simulation every thing went fine.But in real life nothing is good
 

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
Disconnect pin 3 and pin 6 on U2 and see what the output is when you rail the inputs (connect it to pin 7 and then pin 4). Does the output go to at least +12 V and -12 V, respectively?

Try swapping R3 and R4 so as to significantly reduce the gain and see if it works under those conditions.

One thing to be careful about, though it shouldn't be an issue in this circuit, is that U1 must be able to source/sink all of the "ground" currents in the circuit.

Can you look at the signals with an oscilloscope? It could be that the circuit is oscillating and that your meter is therefore reporting values that have little to no meaning.
Now I'v disconnected the pins 3,6 from the feedback and the input signal and converted the circut to the pic i uploaded
On pin 3 = -0.09 v dc
pin 6= 14.55 v dc

unfortunately i don't have access to any oscilloscope is there is any replacement..?
 

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AlbertHall

Joined Jun 4, 2014
12,346
Sure..
Here it is
The Green and white jumpers are the power supply 30 v dc
The Blue and white jumpers are the signal
It is difficult to see where the wires go because of the shadows in the picture but I think there are several errors in the connections, in particular concerned with things which should be connected to U1 pin 6 (the mid- rail '0V') but are not.
The bottom end of R4 is connected to +15V not the mid-point ground.
I can see no connection to U1 pin 7
U1 pin 6 appears to be connected to +15V by a thin green wire (suspect that wire should go to pin 7, not pin 6)
The white wire from your input (not sure which wire it is) isn't connected to U1 pin 6.

Please check carefully the layout compared to the circuit diagram.
 
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