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Peak detector with load?

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FriedMule:
I have made a peak detector
It has zero droop and, do I think, deliver a constant result until shut off
Since KiCad do not have the components I want to use as the Digital Potentiometer I have just put one in the circuit.

Suddenly the thought occurred to me, what if I added an load to the output of the peak detector, would it then work as an PSU with constant, no ripple 5V voltage?
I have added a Zenor (D3) that goes from output to ground if above 5V

741:
Hi

I think there is a mistake with the 2x LM358: A real op-amp will not function reliably/long term with (+) input "floating".
( Have you tried it for real  :)? )

I can not understand how the AD5293 works without any programming-pins (SPI) connected - is this OK? ... what happens to the 'resistor' when the /CS pin is enabled, does it change?


Re: "...would it then work as an PSU with constant, no ripple 5V voltage?"

Although you might see a nice low ripple, that ripple reduction (if any) would come from the U4a's "PSRR", and the peak detector would be "irrevelevant".
That is, U4A's output is not powered by it's signal input.

Best wishes
Stephen

FriedMule:

--- Quote from: 741 on August 27, 2019, 02:33:42 pm ---Hi

I think there is a mistake with the 2x LM358: A real op-amp will not function reliably/long term with (+) input "floating".
( Have you tried it for real  :)? )

I can not understand how the AD5293 works without any programming-pins (SPI) connected - is this OK? ... what happens to the 'resistor' when the /CS pin is enabled, does it change?


Re: "...would it then work as an PSU with constant, no ripple 5V voltage?"

Although you might see a nice low ripple, that ripple reduction (if any) would come from the U4a's "PSRR", and the peak detector would be "irrevelevant".
That is, U4A's output is not powered by it's signal input.

Best wishes
Stephen

--- End quote ---
Thanks for your reply, no I have about no components yet, is just started on the electronical journey:-)
I am trying to learn KiCad but can't get the simulator part to work, lots of "pin not driven" and no lines on the scope even if I tell it where to probe.
I was also a bit confused it's all from the following links: https://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-4
The peak detector is from this video: https://youtu.be/5Pz7Mx0WRUk?t=375

Bassman59:

--- Quote from: FriedMule on August 27, 2019, 03:12:00 pm ---
--- Quote from: 741 on August 27, 2019, 02:33:42 pm ---Hi

I think there is a mistake with the 2x LM358: A real op-amp will not function reliably/long term with (+) input "floating".
( Have you tried it for real  :)? )

I can not understand how the AD5293 works without any programming-pins (SPI) connected - is this OK? ... what happens to the 'resistor' when the /CS pin is enabled, does it change?


Re: "...would it then work as an PSU with constant, no ripple 5V voltage?"

Although you might see a nice low ripple, that ripple reduction (if any) would come from the U4a's "PSRR", and the peak detector would be "irrevelevant".
That is, U4A's output is not powered by it's signal input.

Best wishes
Stephen

--- End quote ---
Thanks for your reply, no I have about no components yet, is just started on the electronical journey:-)
I am trying to learn KiCad but can't get the simulator part to work, lots of "pin not driven" and no lines on the scope even if I tell it where to probe.
I was also a bit confused it's all from the following links: https://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-4
The peak detector is from this video: https://youtu.be/5Pz7Mx0WRUk?t=375

--- End quote ---

For simulation, Kicad uses ngspice. You should look for how to use it. Then there's the question of obtaining models.

Zero999:
It's not the LM358, but the LMV358, which is totally different. It's only rated up to 5.5V and has rail-to-rail inputs. The LM358 is rated up to 30V, but its common mode range is about 2V less than the +V rail, although it can tolerate either input going to 30V, irrespective of the supply voltage.

I don't see how this circuit will work. No op-amp will work with its inputs floating. Pins 5 and 3 on U1 will just pick up stray noise causing the output to flip from 0V to 5V unpredictably.

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