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Power supply for home lab - do I really need a R&S?

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2N3055:

--- Quote from: mhsprang on October 02, 2024, 05:12:53 pm ---
--- Quote from: pdenisowski on May 07, 2024, 04:11:33 pm ---
--- Quote from: thm_w on May 06, 2024, 10:04:18 pm ---You can read some older threads

--- End quote ---

Old indeed :)  Most of the information in those threads is from 2017 or 2020 and refers to the older version, which has been discontinued.  The current HW is the NGE100B

Old:  https://www.rohde-schwarz.com/us/products/test-and-measurement/dc-power-supplies/rs-nge100-power-supply-series_63493-387267.html
New: https://www.rohde-schwarz.com/us/products/test-and-measurement/dc-power-supplies/rs-nge100b-power-supply-series_63493-576967.html

--- End quote ---
But the NGE100B series also has its flaws. One of them is the CC mode.

In constant current mode, the control loop is way too slow. For instance: if you set the voltage to 20V and the current to 10 mA to test a LED and enable the output with a led connected, the voltage will overshoot to 20V for almost 20 milliseconds, before settling on the Vforward of the LED. This will kill the led as the current will be far beyond the maximum limits of the LED.

A test with a 50 Ohm load and a current set to 50 mA let the voltage spike to 18V for 20 ms (I = 360 mA!), after that is decays exponentially over a period of 60 ms to 2.5V (50 mA * 50 Ohm). This is such a serious design flaw that I feel this design should have never made it to market.

This problem has never been fixed in all the firmware updates that have been released over the last couple of years.

--- End quote ---

Control loop is probably not in software but in analog hardware. So no FW can fix it...

nctnico:
I think the control loop is in software though. I have an Agilent 66311B which has the same 'problem' (delayed current limit). If the current limit is done in an analog circuit, then I don't see how you can screw up a power supply circuit that bad. OTOH, it could be done to deal with circuits which have a rush-in current which otherwise wouldn't start up properly. Some DC-DC converter modules are prone to not starting when the current limit is set too low. But I can't see this as a good point on a general purpose lab PSU though.

mhsprang:
I think it's a software loop. The flat top and decay time (see image) are always exactly the same length, no matter the set voltage or current.

mawyatt:
This sort of issue with the R&S PS brings up an interesting point. This can happen even to the best of the best, which R&S is a member.

What really defines the company's character is not that they have a defect/problem/issue, every company will eventually have issues with some product(s), but how they deal with such and how they treat the little folks out there. This exposes the true character of the company hidden within the cloak of famous names/brands/history and such, of course the smaller "Class B" companies have no cloak to hide behind!!

This is one area we use to evaluate companies (or attempt to), even more so now that we are retired (well semi) and paying for all our TE out of OUR pocket, not some big company budget that it completely divorced from what goes on in the labs with folks doing the real work!!

Best

mawyatt:

--- Quote from: mhsprang on October 02, 2024, 08:33:08 pm ---I think it's a software loop. The flat top and decay time (see image) are always exactly the same length, no matter the set voltage or current.

--- End quote ---

That's totally unacceptable behavior from any supply, it's a disaster in the waiting for just about any sensitive electronics use we can think of.

Here's an inexpensive SPD3303X with settings of 20V and 10mA with a Blue LED similar setup and PS settings. Note the DSO Vertical and Horizontal scales, 500mV/Div -2V Offset at 50ms/div.

Best,

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