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What is TL074's output resistance?

stevenh

Guru 20075 points

Other Parts Discussed in Thread: TL074

What is TL074's output resistance?

over 10 years ago

0 Ron Michallick over 10 years ago

TI__Guru**** 174826 points

Steve,

It is 200 ohms.

See figure 6 and image in section 8.2

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Hello Ron,

How do I compute Rout from that figure?

Thanks
Stephen

0 Ron Michallick over 10 years ago in reply to stevenh

TI__Guru**** 174826 points

Steven,

Pick convenient points. I choose 12.6V at 3k ohms and 10V at 600 ohms.
Calculate load current for each point.
Output resistance is (V1 - V2) / (I1 - I2).
I got 208.5 ohms

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Hello Ron,

Where do those values go in the circuit and how did you come up with them?

Stephen

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Ok, I understand. I missed the part about figure 6.

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Hello Ron,

Just wanted to make sure. Is it correct to say the maximum op-amp output voltage is only determined by the op-amp output resistance and load resistance?

Just for my reference, I included the equations and Ro solution (almost same as yours with correction of the sign)

Stephen

(Vx-Vo1)/Ro = IL1

(Vx-Vo2)/Ro = IL2

Then,

Ro = (Vo1-Vo2)/(IL2-IL1)

0 Ron Michallick over 10 years ago in reply to stevenh

TI__Guru**** 174826 points

Steven,

At no load output maximum is not +/-VCC. There is some voltage lost for the headroom needed for the output transistors.
At high frequency, slew rate also limits output voltage maximum.

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Isn't that also true for the loaded condition? If so, Is it valid to use the Max Voltage Output vs Resistance table to compute the output resistance if there are other factors involved?

Stephen

0 Ron Michallick over 10 years ago in reply to stevenh

TI__Guru**** 174826 points

Steven,

I used two real points where I knew output voltage and current (via load resistance).

This current flows through the output resistance and any fixed offset (headroom)

Two points allows getting the resistance without the fixed offset.

0 stevenh over 10 years ago in reply to Ron Michallick

Guru 20075 points

Hello Ron,

I made a mistake in my calculations above. I assumed Vx in the two equations were equal, which is not true. Your equations is about the same Could you please show me how you derived your equation.

Thanks,
Stephen

0 stevenh over 10 years ago in reply to stevenh

Guru 20075 points

Disregard my last post. I am not sure what I was thinking. They are the same.
Stephen