Using one side of a dual opamp

[robkeeler]

If I am only using one side of an op amp (4558 pins 1,2,3,4,8) do I have to connect pins 5, 6, 7 to anything?
Thanks

[brett]

Connect them to each other and Vbias.

[robkeeler]

so 5 to 4......6 to 7?

[markm]

Pins 6 & 7 together and ground pin 5.

[robkeeler]

Since pin 4 is already going to ground can I just attach it to that?


I'm sorry to ask so many questions.  I just want to make sure I get everything right.  Thank you for the help.

[markm]

I suppose you could do that, it's a bit out of the ordinary but, that's DIY! 

[robkeeler]

I just found a diagram in the gallery that uses this concept.

http://aronnelson.com/gallery/Burnt-Fingers-stuff/dist_dual_opamp_perf_asymetrical_clipping_002

[markm]

Well,
There ya go then.....I was right 

[Morocotopo]

From an opamp manual, I think Texas Instrument´s.

Morocotopo

[Peter Snowberg]

The inputs of an opamp should never be parked at the rails.... which means no connections to ground or Vcc.

At Morocotopo posted above, you really want to park unused non-inverting inputs at 1/2 of the way between the supply rails. The inverting inputs should be tied to the outputs and those two should be left floating as the output stage will work to keep the output at the same voltage as the non-inverting input. 

[robkeeler]

Just checking

I would connect 6 to 7 to connect the - input to the output.  Then I would connect 5 to 3  (+ input to the half supply).

[markm]

Well,
There ya go then.....I was right 

Maybe not then. 

[R.G.]

Something most people never think of is that you can connect the output to input on the second opamp, then tie its + input to the output of the other side. It follows the other side, whether it needs to drive anything or not, and it's safe from input common and differential mode problems automatically.

You can also just parallel the +, -, and output pins and have a one package piggyback with twice the current capability out.

[robkeeler]

How does this look R.G.?

[R.G.]

It looks great - except you have swapped 9V and 4.5V. As shown, that won't work, and it will damage some opamps. Put 9V on pin 9 and 4.5V on pins 3 and 5 and you have a good one.

[robkeeler]

Whoops.......thanks for the advice R.G.

[RedHouse]

From an opamp manual, I think Texas Instrument´s.

Morocotopo

And that application sheet says the only reason to use the "Better" circuit (in pic above) is so you can use it later in case you need to.

[Jay Doyle]

From an opamp manual, I think Texas Instrument´s.

Morocotopo

And that application sheet says the only reason to use the "Better" circuit (in pic above) is so you can use it later in case you need to.

That is because, at least how I am reading it, there isn't any difference between those two schems. I guess it means to have 0 ohm resistors in place as well as a space for a resistor to the -in port.

Or am I missing something?