Op amp out puts tied together

[kinarfi]

Can the out put of 2 or more op-amps of a quad op-amp be tied together, each op-amp operating independently of the other to drive a common device with out damaging each other? Or do they need to be diode protected to prevent feed back
Jeff?

 

[MikeMl]

Most opamp have more-or-less symmetrical source and sink currents, so they will be fighting each other.

 

[kinarfi]

Thanks, sounds like a bad idea, I'll use diodes.
Jeff

 

[crutschow]

Thanks, sounds like a bad idea, I'll use diodes.

That will work if you are wanting just a single polarity output such as only plus or only minus voltage. Is that the case with your design?

 

[BrownOut]

If you want to add the outputs, just use resistors.

 

[audioguru]

If the outputs of opamps are tied together then they will not be acting independently. If one output tries to go high when another output tries to go low then there will be high current flowing between them that might cause overheating.

Diodes at the outputs would make a simple OR gate.

 

[kinarfi]

FYI - Here's how & what I'm doing in regards to this question.

Thanks so much.
Jeff

 

[MikeMl]

This will cause the opamp with the higher voltage to control the gate of the NFET. The gate will be one diode drop below the opamp output voltage. I would use Ge or Schottky diodes.

 

[audioguru]

Your diodes make an OR gate.
When one OR both opamp outputs go high then the Mosfet turns on if its gate voltage is high enough.
The outputs of the opamps do not fight.