Designing an IA

MrChips

Joined Oct 2, 2009
27,702
It’s interesting that the scope shows -553V from a 6V circuit.

You show no connection to GND in your 6V power supply circuit.
 

Papabravo

Joined Feb 24, 2006
19,614
I think you might need to connect the battery grounds together. As you have drawn it the grounds are floating with respect to each other. That is NOT the correct way to do things. Connect pin 4 of U5A to pin 4 of U6A and connect both of them to the ground on R12. Can you tell me why you have two batteries V3 & V4 when a single one would suffice?
 

ericgibbs

Joined Jan 29, 2010
16,808
hi MMM.
Where is R12 resistor connected too, it's the divider for Vref.???
E

Update,
You could use the junction in your 4 off battery pack for a 0V.
+2batt 0v 2batt-
 

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MrChips

Joined Oct 2, 2009
27,702
Yes I did this because I have a battery that has positive and negative poles, how to make ground practically?
That is a typical newbie error.

A battery has its terminals labeled with + and -.
This does not mean that the terminals are +ve and -ve.
It only means that one side is 1.5V higher than the other. It is a relative voltage, not absolute voltage.

Connect the ground on the 2 + 2 cell split, (replace 9V with 3V in the drawing):

1670336130313.png
 

Audioguru again

Joined Oct 21, 2019
5,426
https://www.ti.com/lit/ds/symlink/tl082.pdf

see page 11, input common mode voltage range: Vcc-+2 Vcc+0.1
That is only for a new version, a TL082H.
The older version had the -input not working if it is within 4V from the negative supply voltage.

The datasheet for the TL082 recommends a minimum supply that is +5V and -5V.
Your circuit inputs have no DC voltages, they are "floating".
 

Thread Starter

MMM**MMM

Joined May 30, 2022
45
That is only for a new version, a TL082H.
The older version had the -input not working if it is within 4V from the negative supply voltage.

The datasheet for the TL082 recommends a minimum supply that is +5V and -5V.
Your circuit inputs have no DC voltages, they are "floating".
1670340590115.png

Same issue
 

michael8

Joined Jan 11, 2015
333
You power supply for the opamp is +3V and -3V. The inputs to the opamp need to be in the common voltage
range which for +3 and -3 power is +3+.1 and -3+2 or +3.1 and -1 volt. (Someone else said it might be
+3.1 and -3+4 -> +3.1 to +1).

Also your inputs (+ input to U2 and U3) aren't referenced to ground, they are floating. Try adding a resistor
like 100k from each to ground (as a quick fix/check, it's not what you'd do in a real IA circuit).
 
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