# Differential amp

Discussion in 'General Electronics Chat' started by TAKYMOUNIR, Sep 26, 2012.

1. ### TAKYMOUNIR Thread Starter AAC Fanatic!

Jun 23, 2008
352
1
What is the input on pin2 and pin3 and what is the vo
thanks AND IF I NEED THE VO TO BE 10 V WHEN THE INPUT VOLTAGE 1000V WHAT IS THE VALUE OF RESISTORS IN THIS CASE

• ###### DIFF.PNG
File size:
15.2 KB
Views:
33
Last edited: Sep 26, 2012
2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
8,133
1,409
Your drawing is wrong , where is the ground in relation to the battery input?

TAKYMOUNIR likes this.
3. ### ramancini8 Active Member

Jul 18, 2012
473
145
Your circuit doesn't make sense. What are you trying to do?

TAKYMOUNIR likes this.
4. ### TAKYMOUNIR Thread Starter AAC Fanatic!

Jun 23, 2008
352
1
sorry i forget the ground ,i attach new drawing

5. ### TAKYMOUNIR Thread Starter AAC Fanatic!

Jun 23, 2008
352
1
i change the drawing can you look to new schematic
thanks

6. ### Dodgydave AAC Fanatic!

Jun 22, 2012
8,133
1,409
Pin 2 will have 0.6v as the diode d2 is forward biased and the wrong way round, what are the voltages of d1&d2

Zeeus likes this.
7. ### crutschow Expert

Mar 14, 2008
22,479
6,580
The circuit is a differential input design so the differential gain is R5 / (R3+R4) for ideal resistors (much less than 1 in this case). Vo thus is equal to the total value of the input voltage (V1-V2) times this gain value. I'll leave the calculations as an exercise for the reader.

Note that for real resistors you will need to take the resistor tolerance into account.

TAKYMOUNIR likes this.
8. ### TAKYMOUNIR Thread Starter AAC Fanatic!

Jun 23, 2008
352
1
v1-v2=0v or 600v and what is the voltage across d1 and d2
thanks

9. ### TAKYMOUNIR Thread Starter AAC Fanatic!

Jun 23, 2008
352
1
and how can i make vo =10

10. ### Dodgydave AAC Fanatic!

Jun 22, 2012
8,133
1,409
Last edited: Sep 26, 2012
TAKYMOUNIR likes this.
11. ### ramancini8 Active Member

Jul 18, 2012
473
145
The sad news is that unless the external components are matched you get an error because the mismatch creates a differential signal. If you use 3% resistors, and the mismatch between input resistors is 3%, you get an 18V error. Differential amps are very hard to make.

12. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
I'll believe 18mV error.

13. ### crutschow Expert

Mar 14, 2008
22,479
6,580
Dodgydave likes this.
14. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
I think Dodgydave forgot about the feedback.

Dodgydave likes this.