# Op-amp (ua741) with only positive supply voltage

1. Feb 25, 2013

### weitao

Normally the connection of supply voltage is +-V but now is +V and ground.
What happen if Op-amp (ua741) with only positive supply voltage? The op-amp still function?

2. Feb 25, 2013

### skeptic2

Yes it can still function. The +V remains +V, the ground becomes -V and you need to create a pseudo ground in place of the ground. This is usually done with a voltage divider to create a voltage halfway between +V and ground. A relatively large capacitor is usually connected between the junction of the voltage divider resistors and ground, or +V or both.

3. Feb 25, 2013

### weitao

Is it necessary that one of the input (role as voltage reference) must be half of the total of the supply voltage?

4. Feb 26, 2013

### skeptic2

No. It can be anywhere between +V and ground.

5. Feb 26, 2013

### Abstr7ct

What would the capacitor do in the circuit? also, if voltage divider is used, wouldn't that consume power from the power supply?

6. Feb 26, 2013

### skeptic2

If all you want to do is amplify an unchanging DC voltage then you may not need the capacitor. The purpose of the capacitor is to provide a low impedance path to the pseudo-ground. It should do that even at the lowest frequency the op amp will handle. How low of an impedance is for you to decide. If it is not low enough, the pseudo-ground will develop a voltage which may cause positive or negative feedback.

7. Feb 27, 2013

### skeptic2

Yes it will, and if you want a low impedance DC pseudo-ground, it will draw substantial power from the power supply. If you get into that situation you may be able to accomplish the same effect with a high resistance divider and an op amp buffer.

8. Feb 27, 2013

### sophiecentaur

Or use a virtual earth input?

9. Mar 1, 2013

### Staff: Mentor

A google search will turn up plenty of information, e.g., http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf[/color] [Broken]

Last edited by a moderator: May 6, 2017