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Lab Power Supply Turn ON and OFF Characteristics

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Furna:

--- Quote from: mhsprang on October 07, 2024, 11:15:10 am ---
--- Quote from: Furna on October 07, 2024, 09:13:26 am ---
--- Quote from: mahi on October 07, 2024, 04:57:54 am ---
--- Quote from: Furna on October 06, 2024, 08:19:11 pm ---Looking at the datasheet I realized this PSU has also sense wires; did you try using sense?
--- End quote ---

The sense terminals are always in use. In the HMP4040 they are connected to the output terminals via 1.5 kohm resistors inside the power supply. The only moment it makes sense to run separate sense wires to the DUT, is when losses in the wires are relevant. That is not the case in this test.

--- End quote ---

Thank you for your answer; next time I will also read better the datasheet and the manual  :)
Different brand's sense is implemented differently and can be enabled/disabled ...
Now the point is: what is the MCU doing before realizing it is time to lower the voltage?

--- End quote ---

Sense wires have no effect in CC mode. The PSU drives a constant current into the load, no matter what the resistance is. Current flowing through a string of resistors is the same in every single resistor. The test leads are resistors in that chain.

--- End quote ---

All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.

mhsprang:

--- Quote from: Furna on October 07, 2024, 11:37:30 am ---All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.

--- End quote ---

First of all, as a user of a power supply I would like to not be bothered with figuring out how my PSU behaves. I want to read that in the specifications. Second: I sincerely hope that no manufacturer in their right mind would implement the sense system in software! After all, the entire sense-circuit is no more than making the feedback point of the feedback loop available on terminals. Oh crap... that feedback loop!

This brings me back to an earlier statement I made: I think the entire feedback loop of a PSU should not be in software at all unless you have DSP-like capabilities and 100+ kHz ADC/DAC sampling rates.

Just take a beefy power op-amp and use that as a voltage follower after a DAC and there's your digitally controlled, 4 quadrant PSU. How hard can that be? Add a current mirror driven by a second DAC, controlling the output current in CC mode. I remember the application note of the venerable LM12 was full of examples.

And at last, you can add an ADC to actually read back the set values under load.

Furna:

--- Quote from: mhsprang on October 07, 2024, 11:56:01 am ---
--- Quote from: Furna on October 07, 2024, 11:37:30 am ---All correct but if you enable/disable sense, it might alter how the MCU works i.e. more/less MCU cycles before lowering the voltage.
We are speaking about how fast the PSU switches from CV to CC.
Also different materials have different characteristics; 50Ω of wound wire resistor has different inductance than 50Ω of carbon resistor and that matters during power on and switch from CV to CC.
Real world is different than text books.

--- End quote ---

First of all, as a user of a power supply I would like to not be bothered with figuring out how my PSU behaves. I want to read that in the specifications. Second: I sincerely hope that no manufacturer in their right mind would implement the sense system in software! After all, the entire sense-circuit is no more than making the feedback point of the feedback loop available on terminals. Oh crap... that feedback loop!

This brings me back to an earlier statement I made: I think the entire feedback loop of a PSU should not be in software at all unless you have DSP-like capabilities and 100+ kHz ADC/DAC sampling rates.

Just take a beefy power op-amp and use that as a voltage follower after a DAC and there's your digitally controlled, 4 quadrant PSU. How hard can that be? Add a current mirror driven by a second DAC, controlling the output current in CC mode. I remember the application note of the venerable LM12 was full of examples.

And at last, you can add an ADC to actually read back the set values under load.

--- End quote ---

We are going off-topic; this thread is exactly: "How does your PSU behaves when you put it in a crazy condition at Power ON? Take a mesasure with your oscilloscope."
Also I didn't say I want sense systems in software.
I said that taking a measure with sense on/sense off (in case the PSU allows as Siglent SPD4000x series) takes 5 minutes and removes the doubt  8)

pdenisowski:

--- Quote from: mhsprang on October 07, 2024, 09:06:13 am ---Today I received a reply from Rohde & Schwarz: a UPS label and an RMA form to return the unit.

I replied that I won't be returning my PSU because the problem is not exemplary but a design error. I told them they can take any NGE100 or other model from their inventory and reproduce this problem.

I also included the links to both threads on this forum.

Whenever I hear more from them, I will post it here.

--- End quote ---

We are still actively investigating this issue, and I've been in direct communication with the product manager and our technical expert since you made your first post about this last week. I had already sent them these threads for reference as well.  I also just PM'ed you my email address so that you can reach our to me directly.

Although many of our product managers and R&D engineers do read EEVblog and watch YouTube, contacting us directly would likely be a much more efficient form of communication.  I can assure you that we take this (and all other) customer issues seriously, so please feel free to email me directly if you have any concerns or questions.

mawyatt:
With the new Siglent SPD4000 series we find it interesting that the results from CH1 and CH2 are different wrt to the conditions discussed here as shown by Furna. We don't see this with the older SPD3303X as both channels behave the same as expected!! Also, haven't seen any post that indicate other supplies have different behavior with 2 main channels with same specs as one would "expect" the detailed design and implementation of the channels would be identical. 

Would be interesting to find out why, as this is quite puzzling?

Best

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