[SOLVED] Power supply for opamp

[snishanth512]

I am using op07 opamp.



I connected 2 separate power supplies for opamps.

one for +5v and another for -5v.

My doubt is that, do I need to ground the power supplies separately (i.e. not grounding with circuit flow)?

What will happen in real time ?

 

[BradtheRad]

Ground will be the node where the + of one supply is connected to the - of the other supply.

Your input and output are referenced to that connection.
All of your ground icons are attached to that connection.

 

[sgreen]

Of course you should use a common ground for both power supply.

 

[BradtheRad]

All we can do is guess, unless your schematic were to show your power supplies and how they are hooked up.

 

[crutschow]

In general, unless there is some intentionally isolated portions of a circuit, power supplies and circuits must all be referenced to a common point (called common or ground).

 

[snishanth512]

I implemented the circuit in the breadboard.

Input : 2v peak to peak sine wave of 4 Hz.

The output was displayed using DSO.

But the signal was corrupted with more noise.

When I connect the ground separately (i.e. I connected all "gnd points" given in picture but not the power supply gnd point)

Input was same.

But the output was free from noise.

only the signal got attenuated.

why is that so ?

 

[vimalkhanna]

Put a small feedback capacitor of 1kpf from output terminal to inverting input to quench the noise .
As it is ,a common ground between the supplies must be connected to load ground requirement.

 

[snishanth512]

I didn't get you.

Where to place the capacitor ?

I am using two 7805 voltage regulator for opamp power supply.

one for +5V and Other for -5V.

 

[sgreen]

I didn't get you.

Where to place the capacitor ?

I am using two 7805 voltage regulator for opamp power supply.

one for +5V and Other for -5V.

How do you believe 7805 will work for both +5v and -5V volt generation? You have to use 7905 for -5V.

 

[snishanth512]

How do you believe 7805 will work for both +5v and -5V volt generation? You have to use 7905 for -5V.

Reverse the polarity.

 

[BradtheRad]

Reverse the polarity.

Great idea...
Unfortunately however, current will refuse to flow in the direction you need.

The 7805 (+5V regulator) IC only has current flowing OUT of the regulated terminal. Current cannot flow backwards through it.

Therefore two 7805 regulators cannot create a bipolar supply to power an op amp.

To provide a negative supply, you need to have current flowing into the regulated terminal.
This requires a P-device operating internally (whereas a positive supply uses an N-device internally).

This schematic will do about the equivalent job of a 7905 IC (-5V regulator):