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  • Author Author: jw0752
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Playing with an OP 191 Op Amp

jw0752

One of the really great things about the E-14 Web Site is how much one can learn just by reading and paying attention to some of the threads. On Jan 9th posted information on the OP191 and OP192 Op Amps which he likes to use in his designs. Being curious to play with them for myself I marked down the number and ordered some of the OP 191 for my shop. The OP191s that I received were in the SOIC8 package so it was necessary to mount it on an adapter board so that I could conduct some simple experiments on the bread boards. Here is the OP191 after I mounted it on the adapter and turned it into a DIP8.


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I next built a simple circuit with a gain of 10 and used my wave form generator and my oscilloscope to look at the limits of the chip and how well it performed. Here is the simple circuit.


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I used a +/- 10 volt supply for the chip and I ran the input level down until I could no longer get good readings on my scope. I was very impressed with how well the OP191 worked. Actually it doesn't take that much to impress me or to cover my needs. I could have taken 's word for it but what would have been the fun in that? The Op Amp did a very good job reproducing sine, square, and ramp inputs.


Here are the readouts of the test equipment during one of the experiments on the Op Amp.


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Thanks again to MK for the excellent recommendation and all the fun I had tonight playing with the OP191. It will be fun to use it in my next build that requires this level of Rail to Rail Op Amp. If you want to read MK's original post it is in this thread


Power Supply for Home lab?

by


John.

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  • Ah, the website is back and working.

     

    I'm having great fun with this simulation stuff. Another circuit you might want to try is an "ideal diode". You often used to see this circuit on old op-amp datasheets - particularly the wonderful ones that Nat Semi put out with dozens of circuits on them - but I've never had a use for it in real life.

     

    Here's the circuit

    image

     

    here are the waveforms for a 5kHz sine wave going in

     

    image

     

     

    Although it is far superior to the 1N4148 by itself, it's not quite perfect. The small step on the output as the input cuts 0V on the way up is where the opamp output has to suddenly move from close to the -12V rail to the 0.6V it needs to forward bias the diode and start lifting the output. That change is limited by the slew rate of the amplifier output.

     

    This shows that point in more detail (green is the input, red is the output)

     

    image

    The datasheet gives the slew rate as 7V/uS typical (rising), so that suggests 1.8uS for the -12V to 0.6v transition plus a bit of settling time. The simulation is about 3uS, so it looks like the model is safely worst-case and you'd see something faster than that if you measured it (which you should be able to do easily if you look at the input and output on a scope and place them on top of each other). It's encouraging that the TI model seems to be this detailed.

Comment

  • Ah, the website is back and working.

     

    I'm having great fun with this simulation stuff. Another circuit you might want to try is an "ideal diode". You often used to see this circuit on old op-amp datasheets - particularly the wonderful ones that Nat Semi put out with dozens of circuits on them - but I've never had a use for it in real life.

     

    Here's the circuit

    image

     

    here are the waveforms for a 5kHz sine wave going in

     

    image

     

     

    Although it is far superior to the 1N4148 by itself, it's not quite perfect. The small step on the output as the input cuts 0V on the way up is where the opamp output has to suddenly move from close to the -12V rail to the 0.6V it needs to forward bias the diode and start lifting the output. That change is limited by the slew rate of the amplifier output.

     

    This shows that point in more detail (green is the input, red is the output)

     

    image

    The datasheet gives the slew rate as 7V/uS typical (rising), so that suggests 1.8uS for the -12V to 0.6v transition plus a bit of settling time. The simulation is about 3uS, so it looks like the model is safely worst-case and you'd see something faster than that if you measured it (which you should be able to do easily if you look at the input and output on a scope and place them on top of each other). It's encouraging that the TI model seems to be this detailed.

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