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schematic

simulate this circuit – Schematic created using CircuitLab

This is the circuit schematic of an astable multivibrator. I have to chose the resistance value of R3 in order to limit the output current of the OpAmp. The OpAmp model is TL081 Texas Instruments, and this is the link to its datasheet . I am not able to find any information about the maximum output current in it. Can anyone help me? I have another question: is there any other reason why the resistor R3 is necessary in this circuit ?

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2 Answers 2

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In the data sheet there are hints about what you can load the op-amp with. The maximum peak-to-peak output voltage when loaded with 10kohm is guaranteed to be +/-12V on a +/-15V supply regime.

When loaded with 2kohm the max voltage is somewhat less at +/-10V.

I would usually consider that 2kohm loading is the minimum you should have.

All that info is on page 6 of the DS. I would also look at these graphs for what to expect at lower suply voltages: -

enter image description here

These are on page 9 and page 10 gives you more information when the ambient temperature is different. See also this graph on page 10: -

enter image description here

I am not able to find any information about the maximum output current in it.

The last graph should give you the information you need and you should probably consider 1kohm for R3

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  • \$\begingroup\$ Is there any problem if the real Peak Output Voltage is 14.2V (I measured it) ?If I have undestood correctly I should chose a 4k resistor. \$\endgroup\$
    – gilgamesht
    Nov 29, 2015 at 12:07
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    \$\begingroup\$ I would calculate the power dissipation in the op-amp to make sure it doesn't get too warm but, for current a 4kohm should easily be fine. If the peak is 14.2V (I'm surprised it's as high as this from a 15V rail) then the power dissipated in the op-amp for that positive swing is going to be 0.8V * current and current will be 14.2 volts /4k = 3.6mW. Sounds OK to me. \$\endgroup\$
    – Andy aka
    Nov 29, 2015 at 12:12
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I know this is an older question but I found it when I searched for a similar answer. I found in the TL081datasheet that the maximum output current is 60mA, and minimum is 10mA. These values are for output short-circuit current so I take them as the maximum that I can drain from that opamp.

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  • \$\begingroup\$ I don't think this tells the OP what he needs to know. That's the numbers that are caused by an output short, but doesn't tell how much current can be drawn before "normal" output behavior is no longer guaranteed. \$\endgroup\$ Jan 9, 2020 at 15:10

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