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compensation Diode on Opamps Pins 1 and 8

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ParkerMike

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What is this Diode doing on the Op amps pin#1 and Pin#8?

I mostly see a capacitor on the Op amps pin#1 and Pin#8

Compensation Diode.jpg
 

The very old opamp does not have any negative feedback (it is used as a comparator) so it does not need a compensation capacitor (not diode) between pin 1 and pin 8.
The diode might be used as a voltage clamp.
 

The diode might be used as a voltage clamp.
Click to expand...

Wouldn't a zener diode be better to use for a voltage clamp?

How does pin#1 and pin#8 clamp the voltage of the output?
 

The question is rather specific and can't be answered without analyzing the LM101 internal circuit. You'll find it in the datasheet.

Your circuit differs from the clamping options suggested in the datasheet and I wonder if it is effective at all. LM101 isn't designed as a comparator, maybe the diode is sligthly speeding up the response.

As in most electronic circuits, you'll find that there are boundless possibilities to achieve a specific purpose. It's often easier to design your own solution than analyzing an existing circuit exhaustively.
 

the diode is sligthly speeding up the response.
Click to expand...

How does the diode speed up the response time? how so?

what is your theory behind this
 

The "theory" is that the diode may prevent saturation of Q9 (see transistor level schematic in the LM301 datasheet). On the other hand, the diode capacitance reduces the output slew rate.
 

The "theory" is that the diode may prevent saturation of Q9 (see transistor level schematic in the LM301 datasheet).
Click to expand...

So it does Clamp the output voltage?

On the other hand, the diode capacitance reduces the output slew rate.
Click to expand...

True, very good FVM
 

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