[SOLVED] Unity Gain Differential Amplifier Issue

[djeceymca]

Hello Guys,

I and trying to create a Unity Gain Differential Amplifier using LM324 opamp. Circuit diagram as below, In this all resistance are of 10k values. Theoretically output should be difference of both the inputs but somehow the result are totally different.

Supply voltage: 5V
Input voltage: 3.24V
Output voltage 1.1V and decreasing if keep connecting voltmeter.

Could you please guys help me out here.



Regards,
Dev

 

[FvM]

Not clear what "input voltage 3.24V" means, the circuit has two inputs respectively common mode and differential input voltage.

Report complete test setup.

 

[KlausST]

Hi,

I agree with FvM.

Mind that the "input voltage" with this difference amplifier is defined as: V_in = V2 - V1

In any case you have to take care that the Opamp input voltages are within specified range.
And mind that the output voltage will never reach the supply voltage rails...there will always be some dropout voltage.

Klaus

 

[RobertFalbo]

I hate to ask, but do you have the supply voltage connected to the right pins. Positive rail on Pin 4 of a quad.

where on dual op-amps pin 4 is ground.

 

[djeceymca]

Hello Guys,

Thanks for your valuable response.
Input Voltage 3.24V means 3.24V battery connected between V2 and V1.

Next day I tried with same circuit and it worked. Must be some problem with connection.

Sorry for wasting your time.

Regards,
Dev

 

[KlausST]

Hi,

from post#3:

In any case you have to take care that the Opamp input voltages are within specified range.

What you describe could be caused by not taking care about this.
How do you ensure that you are within the specified limits?

Klaus

 

[RobertFalbo]

Hello Guys,

Thanks for your valuable response.
Input Voltage 3.24V means 3.24V battery connected between V2 and V1.

Next day I tried with same circuit and it worked. Must be some problem with connection.

Sorry for wasting your time.

Regards,
Dev

is the only connection to the battery the V1,V2 ?

Is the power supply for the amp 'floating' with the battery?

 

[djeceymca]

Only battery connected to V2 and V1, there is separate 5v supply voltage for opamp.