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Using OpAmps as Voltage Regulators
Using OpAmps as Voltage Regulators
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Old 23rd March 2020, 07:46 PM   #31
jackinnj is offline jackinnj  United States
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Using OpAmps as Voltage Regulators
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Originally Posted by Tfive View Post
Would you care to cite a reference please? Or did you simulate that? Or even measure it?
Use an OPA1622 wired for unity gain with a 3.3V non inverting input, place ferrite bead (90n||100R), 100u aluminum electrolytic and 10u ceramic on the output and look at the impedance. It's two orders of magnitude higher impedance.
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Old 23rd March 2020, 07:49 PM   #32
Tfive is offline Tfive  Germany
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Would you say that's still true without the ferrite bead? I mentioned in the first post that I think the ferrite bead will have to go because of it's too high impedance/resistance even at low(ish) freqs.
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Old 23rd March 2020, 07:59 PM   #33
MorbidFractal is offline MorbidFractal
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Originally Posted by Tfive View Post
@MorbidFractal: I just installed LTSPICE, opened the simulation files you provided and got a weird result (attached). So I guess I have to adjust some simulation options... I clicked through them but can't seem to find anything obvious. Probably bloody beginners fault
Depending on the analysis you are doing you have to set VAC or IAC to 1 with the other being 0. In the one your picture shows. Set IAC to 0 and VAC to 1. Right click. Click on Advanced. AC is on the upper middle right.

Oh... or you can just right click on the AC 1V and edit it directly.

Last edited by MorbidFractal; 23rd March 2020 at 08:03 PM.
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Old 23rd March 2020, 08:12 PM   #34
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Tfive View Post
@MorbidFractal: I just installed LTSPICE, opened the simulation files you provided and got a weird result (attached). So I guess I have to adjust some simulation options... I clicked through them but can't seem to find anything obvious. Probably bloody beginners fault
You are measuring the voltage across a voltage source. Of course that is constant ...

Jan
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Old 23rd March 2020, 08:19 PM   #35
Tfive is offline Tfive  Germany
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Got it to work, thanks for all your help. Will experiment with this the next days.
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Old 23rd March 2020, 08:22 PM   #36
MorbidFractal is offline MorbidFractal
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Quote:
Originally Posted by jan.didden View Post
You are measuring the voltage across a voltage source. Of course that is constant ...

Jan
It's non-intuitive.

Does my head in as well but you are measuring the ratio of either side of the voltage source with respect to ground.
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Old 23rd March 2020, 08:23 PM   #37
Tfive is offline Tfive  Germany
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My problem was that I didn't know how to enter the expressions to plot.
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Old 23rd March 2020, 08:27 PM   #38
MorbidFractal is offline MorbidFractal
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Is that was or is it still is?

If you click on a node in the circuit it will plot it. If the node does not have a label it will have been given a number. If you then right click on the plot label you will be given the opportunity to edit the expression.
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Old 23rd March 2020, 08:29 PM   #39
Tfive is offline Tfive  Germany
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It was. I've gone via right clicking the plot window => add trace => enter the expression in the input field on the bottom.
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Old 23rd March 2020, 08:33 PM   #40
MorbidFractal is offline MorbidFractal
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Blooming expert.
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