Connecting Dual Supply Opamps in a Single Supply Circuit with Transistors

Click For Summary

Discussion Overview

The discussion revolves around the challenge of integrating dual supply operational amplifiers (opamps) into a circuit originally designed for single supply operation, specifically using the LM324. The context includes considerations for precision, signal characteristics, and the use of transistors within the circuit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the connection of dual supply opamps in a single supply circuit and mentions the presence of PNP and NPN transistors.
  • Another participant suggests using a precision band gap reference to create a virtual ground, noting that implementation depends on factors such as precision requirements and frequency range.
  • A different participant asks about the available power rails, the reason for not using single-supply CMOS opamps, and requests details about the signal voltage range and the opamp's intended gain/functionality.
  • One participant describes a method for creating a virtual ground using a resistor divider and a unity gain op-amp buffer, while also mentioning alternative methods that may be cheaper or better.

Areas of Agreement / Disagreement

Participants present various methods and considerations for connecting dual supply opamps in a single supply circuit, but no consensus is reached on a singular approach or solution. Multiple competing views and suggestions remain in the discussion.

Contextual Notes

Limitations include the lack of specific details about the circuit's requirements, such as precision levels, signal characteristics, and the exact role of the opamps and transistors. The discussion does not resolve the effectiveness of the proposed methods.

m718
Messages
88
Reaction score
0
I have a circuit with single supply lm324 and I need to replace them with precision opamps but I can only get dual supply ones. How would I connect the dual supply opamps in the circuit?
(the circuit also has PNP and NPN transistors).
 
Engineering news on Phys.org
Use a precision band gap reference to generate a virtual ground if feasible. They come in several flavors, 1.23V, 2.5V, 5.0V, etc.

Exactly how you can implement what you want depends on a lot of factors, like how much precision, what frequency range, where does the precision have to be, etc.
 
What power rails do you have available? Why can't you get single-supply CMOS opamps? Have you done much searching? What voltage range is your signal, and what kind of gain/functionality are you using the opamp for?
 
For single supply operation, I usually make a "virtual ground." Make a resistor divider from Vcc to ground and bypass it with a cap to ground (2x100K resistors and a .1uF). Then, follow it with a unity gain op-amp buffer (use a cheap op amp).

Put a 33 ohm resistor between the output of the op-amp and the "virtual ground," and bypass the virtual ground to real round with a 47 - 100uF cap.

There are cheaper ways, and there are better ways, but you can usually depend on this method without taking more into consideration.

- Mike
 

Similar threads

  • · Replies 17 ·
Replies
17
Views
2K
Replies
11
Views
3K
Replies
12
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
Replies
68
Views
7K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 15 ·
Replies
15
Views
5K
Replies
7
Views
3K