difference between negative supply and ground???

[shaiqbashir]

Hi Guys!

well! i have seen in many circuits diagrams that there are some connections to a negative supply lets say "-5V" and some to grounds.

now i want to ask you that what is the difference between them?

actually i want to know it like this that while making a circuit how we have to configure a negative supply and a ground?

is it true that battery's negative side serves as the circuit ground. If no then how we actually develp a ground in a circuit.

Thanks in advance!

 

[audioguru2]

Hi Shaiq,
Many circuits must operate with their input or output at ground. But ordinary opamps don't work with their inputs or output at their negative supply voltage, so they use a negative supply to allow their inputs and output to work at ground. The ground is where the positive supply and negative supply are joined. ;D

 

[jstevenperry]

Oh great, audioguru, please lend us your wisdom and expand on your comments. An op am relies on differential voltage (so that it may amplify accordingly), but please explain how to supply a "negative" voltage to any given circuit (and what that means). This concept has eluded me as well.

Thanks.

 

[audioguru2]

Hi Jspn,
I've already said it. Ordinary opamps don't work if their inputs or output voltage is near their negative supply voltage. So you connect a negative voltage to the negative supply pin then they can operate fine with their inputs and output voltages at ground.
If you connected their negative supply pin to ground, then they won't amplify anymore if the input voltage is about 2V or less and the output will never be less than about 1V.

A negative supply voltage can be made with a transformer and a rectifier, or a second battery with its positive terminal connected to ground.