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TINA spice simulation gives floating warnings
TINA spice simulation gives floating warnings
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Old 6th November 2019, 06:15 PM   #41
inkl is offline inkl  Russian Federation
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ok, I added R5=47 Ohm and now I have the following:


Click the image to open in full size.


gain:


Click the image to open in full size.


so why is this R5 is so critical?


Well, I just started reading about op amps...
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Old 6th November 2019, 06:19 PM   #42
audio_tony is offline audio_tony  United Kingdom
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Quote:
Originally Posted by inkl View Post
ok, I added R5=47 Ohm and now I have the following:
so why is this R5 is so critical?
Briefly;

R5 will isolate the opamp from a capacitive load, and prevent oscillation.

Here is a very detailed explanation.
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Old 6th November 2019, 06:27 PM   #43
inkl is offline inkl  Russian Federation
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I just found out that if I set the voltage back to 3,3V I get that weird gain curve again. And it stays the same no matter if there is R5 or not. But increasing VCC to 5V gets back things to normal...
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Old 6th November 2019, 06:31 PM   #44
audio_tony is offline audio_tony  United Kingdom
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Quote:
Originally Posted by inkl View Post
I just found out that if I set the voltage back to 3,3V I get that weird gain curve again. And it stays the same no matter if there is R5 or not. But increasing VCC to 5V gets back things to normal...
That's because the supply voltage is too low for the required gain.

By the way, the LT1215 is not a good choice for your application, it looks to have a high noise figure.

Try using an NE5532 for your sims because once that works reliably you can then try alternate OPAMPS.
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Old 7th November 2019, 08:38 PM   #45
inkl is offline inkl  Russian Federation
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ok, I made another one, from Project 93:


Click the image to open in full size.


But here's what I get in the diagram:


Click the image to open in full size.


I don't get what it means? Also, I'm not sure I put that zener diode right. Can you please let me know what's wrong with it? The simulation seems to be correct...
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Old 7th November 2019, 08:55 PM   #46
audio_tony is offline audio_tony  United Kingdom
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Setup some test points around the circuit and do a DC simulation, take a screenshot and post it here.

It's highly unlikely this circuit will offer better performance and gain than an OPAMP though.
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