Power supply for home lab -  do I really need a R&S? - Page 1
Forum section: electronics / testgear

author: FranciscogGomez
author_rank: Contributor
timestamp: May 06, 2024, 04:23:45 am
content: Hello everyone,A couple of weeks ago I sold my cheapy single-output power supply for good beacuse it is time for me to buy a more decent power supply for my home lab. it will be used mainly for my personal project but also on project from work (HO). These are the requirements:Hard requirementstwo or three independent outputsProtections: OCP & OVPVoltage accuracy: <=10mVUSB or ETH port for basic controllingMild requirementsSequencing/programmable feature (it's a nice plus)Lightweight. (Linear power supply is not a hard req.)Price: ~500EUR & ~800EURI have narrowed down my list to the following table:The best option that I have is the GPP-4323(dark green)butmy "professional-side" inner voice it is telling me that the NGE-100 series is a good option for me as well. (realistically, a used one)I want to debunk the need of a power supply from Rohde & Schwarz and for this, I need your help.so my question is:has anyone bought a power supply from the NGE-100 series and regretted it?if so, could you tell my why?CheersFrancisco

author: jonpaul
author_rank: Super Contributor
timestamp: May 06, 2024, 04:57:01 am
content: Dear Sr. Gomez:Very fine and detailed post.We can assit you better if you can precice your applications and experience:eg: you are Beginner, amateur radio, techincial, emgineer, ?uses: Testing and developing microcontrollers?General analog circuits?Batterty charging?As a hobbyest since 1950s and Electrical enginer since 1968, we always used HP, Lambda, Tek dual or triple linear supplies with analog meters.We have paid $US 10..50..75..and $250 max.We found thewm on epay, Ham radio fleas, local asds like craig list etc.We have no idea for the Chinese or Rhode and Schwartz you seem to be prefering.We are wary of fancy digital controlled PSU as they are no as reliable or robust compared to simple linear.Bon chanceJon

author: Hacked
author_rank: Contributor
timestamp: May 06, 2024, 05:52:19 am
content: Hello,Here is PSU from UNI-T:https://eleshop.eu/uni-t-udp3305s-power-supply-5976.htmlI ordered that one two days ago, it should get delivered this weekPeople sad good things about that PSU, and it checks most your requirements, and price is great.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 06, 2024, 06:59:56 am
content: Minor remark: if you're actually looking for a 10mV accuracy on your DUT, you kinda need remote sensing. Otherwise, that 10mV is just a number on a screen ;-)

author: nctnico
author_rank: Super Contributor
timestamp: May 06, 2024, 07:14:36 am
content: I'm missing the Keysight E36313A from the list. A rather unique feature is that it has two current ranges so it can measure low currents more accurately compared to other PSUs.

author: J-R
author_rank: Super Contributor
timestamp: May 06, 2024, 10:32:55 am
content: Overall the E36313A is pretty great, with its available rear outputs + sense but you'd have to find a used one to have any hope of reaching the target price point.Biggest flaw in my opinion with the E36300 series is the front panel control knob UI. You can't select a specific digit to adjust up and down, so you're left with a somewhat crude acceleration feature. If you want to do 100mV steps, you would need to program it to do that. I use the keypad exclusively so no issue personally and I have other bench supplies with better knob UIs.The GPP-4323 isn't perfect either, there are reports of recent firmware issues as well as some other items. Also, the load feature has some limitations, such as 1.5V minimum operating voltage.Could also add Rigol to your list.

author: blackdog
author_rank: Frequent Contributor
timestamp: May 06, 2024, 10:49:07 am
content: Hi,My preference is completely analog as far as power supplies are concerned.And I mean the control part, the older HP/Harrison models are excellent, even for contemporary applications.On my two workbenches are modern GW-Instek analog models and older HP power supplies.What I have seen from testing regarding R&S power supply's, that does not make me happy.Poorly regulating current limitation and digital pre-regulation despite the advantages regarding energy consumption I am also not in favor of due to the commonmode injection of interfering signals.If you have a power supply with mV resolution this can be very useful, but keep in mind the accuracy specification.If you really want to know mV accurately, a DMM is still often needed, especially with the larger currents, and as already indicated, remote sensing is then also needed.A lot depends on what is important to you, for me that is a low level of interference when I am developing something, that does not include an EMC lighthouse, as far as LAB power supplies are concerned.I've had a Dutch DELTA 30V switcher, 5-Ampere LAB power supply.So far, that's the only one I've had on the workbench that I could live with a little bit regarding interference level and EMC.But because of the very strong filtering, the current limiting was a bit too slow for sensitive circuits.I have two pieces of GW-Instek GPP-4323 power supply and am happy with them.If you have the budget, go for the LAN version, that makes it easier to manage the power supply through Testcontroller if you find this easy.Furthermore, there are people on this forum who make adjustments to the firmware of these power supplies, look it up.Greetings,Bram

author: rsjsouza
author_rank: Super Contributor
timestamp: May 06, 2024, 11:18:56 am
content: Quote from: nctnico on May 06, 2024, 07:14:36 am+1 vote for the Keysight model. The low resolution is a very good time and space saver (as I don't need several DMMs around)Quote from: J-R on May 06, 2024, 10:32:55 amAnother annoyance is its standby without a native "mechanical power switch", which leaves the backlight on and, at times, I hear the transformer buzzing if I have certain types of loads on the same 120V circuit (not entirely the fault of the PS but a power switch would minimize that).

author: HalFoster
author_rank: Frequent Contributor
timestamp: May 06, 2024, 12:28:53 pm
content: My suggestion would be a (linear) Siglent SPD3303X for a new supply - I have a couple and am very pleased with their performance. Although if you don't mind analog meters a vintage HP, Kikusui or such are very, very good performers and are pretty much bulletproof.Hal

author: mawyatt
author_rank: Super Contributor
timestamp: May 06, 2024, 02:07:17 pm
content: Agree the SPD3303 are pretty good for the $ (which can be "enabled" for 1mv, 1ma resolution), we have 3 as well as GPP4323. Both types are good and don't exhibit any "surprises" at Turn ON/OFF.The UI for the 3303 is a little quirky, but one gets used to it quickly, and the terminal spacing isn't standard, but for the $ a good value IMO. GPP4323 is more expensive but has 4 channels and also quite good.Best,

author: temperance
author_rank: Super Contributor
timestamp: May 06, 2024, 03:24:09 pm
content: No TTi power supplies in the list? I have three TTi power supplies and they are all pretty good.I really like the PL303 QMD.2 x 30 V, 3 A.-Can work in tandem, parallel, independent. (both channels are isolated)-OVP-Fine adjust for the voltage.-Two current ranges. 500 mA and 3 A.-Lockable-Lockable voltage range (you can set min. max voltage over which the output can be adjusted)Inexpensive for what you get. Non switching so no common mode noise all over the place.

author: nctnico
author_rank: Super Contributor
timestamp: May 06, 2024, 03:43:18 pm
content: Quote from: temperance on May 06, 2024, 03:24:09 pmI'm not impressed. I'm not a fan of PSUs with coarse / fine control. A 10-turn pot doesn't cost that much.

author: Rydda
author_rank: Contributor
timestamp: May 06, 2024, 06:38:38 pm
content: I have the R&S NGE103, and I am very fond of that one. Especially since the fan turns off at low currents. But be aware that the max power output per channel is 33.6 Watt ,so you cannot do 32V @ 3A .

author: temperance
author_rank: Super Contributor
timestamp: May 06, 2024, 08:42:16 pm
content: QuoteNot to mention that power supplies with ten turn pots are rather rare.

author: tautech
author_rank: Super Contributor
timestamp: May 06, 2024, 08:47:47 pm
content: Quote from: temperance on May 06, 2024, 08:42:16 pmAnd painful to use when large adjustments are required.

author: nctnico
author_rank: Super Contributor
timestamp: May 06, 2024, 09:57:52 pm
content: Quote from: temperance on May 06, 2024, 08:42:16 pmNot at all. All the older quality power supplies from respectable brands like HP/ Agilent, Delta, etc have ten turn pots. Nowadays you even find these on el-cheapo Chinese power supplies (if they have analog controls).

author: thm_w
author_rank: Super Contributor
timestamp: May 06, 2024, 10:04:18 pm
content: E36313A is $2,200 which is a large step up in price, at that point you should compare it to the NGC100/NGL200/etc. I don't think its relevant to this discussion.I wouldn't buy NGE100 unless it were <$500 used, you can read some older threads:https://www.eevblog.com/forum/testgear/newly-released-entry-level-rs-nge100-power-supply-series/https://www.eevblog.com/forum/testgear/rs-nge100-voltage-jumping-around/There is also the UDP3305S:https://www.eevblog.com/forum/testgear/uni-t-udb3000s-series-udp3305s-udp3000s-e/msg5455556/#msg5455556Rigol you'd be looking at DP2031 or DP932U:https://www.rigolna.com/products/dc-power-loads/dp2000/dp2031/Which I don't recommend at this time due to the poor font used.

author: FranciscogGomez
author_rank: Contributor
timestamp: May 11, 2024, 05:37:17 pm
content: Hello and sorry for my late respsonse,I will address/ comment back to most of the comments in this one:Quote from: jonpaul on May 06, 2024, 04:57:01 amHello Jon,I'm an electrical engineer and my projects are 90% digital embedded systems-related, the 10% extra will be RF & analog circuits (few occasions now and then)------------------------------------------------------------------------------------Thanks for your recommendation Hacked; and for the remark Ice-Tea, it's a good one to keep in mind.------------------------------------------------------------------------------------Quote from: nctnico on May 06, 2024, 07:14:36 amThe reason is not the list is beacuse the price, way out of budget.Quote from: thm_w on May 06, 2024, 10:04:18 pmthm_w, Spot on!Thanks, I'll trying to get one around that price range +/-150EUR. For the Rigol PSU, I personally don't like their front panel presentation. (for this reason, I did not add them to the list)Quote from: blackdog on May 06, 2024, 10:49:07 amQuote from: blackdog on May 06, 2024, 10:49:07 amThanks for your comment and hint, BramQuote from: temperance on May 06, 2024, 03:24:09 pmthanks, temperance. I have added the PL303QMD-P. With -P in order to have the ports for remote control. However, the price is close to the R&S. I'll keep an eye on this one on the second hand market as well.

author: FranciscogGomez
author_rank: Contributor
timestamp: May 11, 2024, 05:38:36 pm
content: Quote from: Rydda on May 06, 2024, 06:38:38 pmhey Rydda, You are right! I overlooked this important specification from it

author: FranciscogGomez
author_rank: Contributor
timestamp: May 11, 2024, 05:43:13 pm
content: Based on your previous comments and suggetions, I have update my list:

author: Lochstreifen
author_rank: Newbie
timestamp: May 11, 2024, 05:56:44 pm
content: Some years old, but nice overview of multi channel PSUshttps://goughlui.com/2019/07/28/rs-hmc8043-psu-review-in-depth-ch1-market-survey/

author: FranciscogGomez
author_rank: Contributor
timestamp: May 11, 2024, 06:11:13 pm
content: Quote from: pdenisowski on May 06, 2024, 03:49:24 pmhey pdenisowski,For sure R&S make nice power supplies and I do like the build quality of them(hats off). That's why I'm considering to get one. However, the reason I want to debunk the need of a power supply from R&S is from the point of view of single person/engineer with a lab. at home and limited budget compare to a company.For the price of a NGE103b, I can get a mid-quality but decent power supply (that will do its job) for less money; which will leave my wallet with extra cash to get more equipment.What I'm looking for is to learn from experiences from colleagues that had experienced this dilemma beforeRegards

author: FranciscogGomez
author_rank: Contributor
timestamp: May 11, 2024, 07:04:16 pm
content: Quote from: Lochstreifen on May 11, 2024, 05:56:44 pmThanks Lochstreifen,I really do liked this post. well... Part1, I still need to read up to Part6.

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2024, 11:27:25 pm
content: Quote from: FranciscogGomez on May 11, 2024, 05:43:13 pmIf you're not in a hurry one of the SPD4000X PSU's coming in a month or 2 might be of interest.https://www.siglent.com/products-overview/spd4000x/You've not listed any hard V/A requirements ?

author: mhsprang
author_rank: Regular Contributor
timestamp: October 02, 2024, 05:12:53 pm
content: Quote from: pdenisowski on May 07, 2024, 04:11:33 pmBut 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.

author: 2N3055
author_rank: Super Contributor
timestamp: October 02, 2024, 08:01:40 pm
content: Quote from: mhsprang on October 02, 2024, 05:12:53 pmControl loop is probably not in software but in analog hardware. So no FW can fix it...

author: nctnico
author_rank: Super Contributor
timestamp: October 02, 2024, 08:27:40 pm
content: 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.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 02, 2024, 08:33:08 pm
content: 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.

author: mawyatt
author_rank: Super Contributor
timestamp: October 02, 2024, 11:50:01 pm
content: 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

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 12:28:36 am
content: Quote from: mhsprang on October 02, 2024, 08:33:08 pmThat'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,

author: moerm
author_rank: Regular Contributor
timestamp: October 03, 2024, 12:50:27 am
content: Quote from: FranciscogGomez on May 11, 2024, 05:38:36 pmNot only that one...[quote author=FranciscogGomez link=topic=427153.msg5494642#msg5494642 ey pdenisowski,For the price of a NGE103b, I can get a mid-quality but decent power supply (that will do its job) for less money; which will leave my wallet with extra cash to get more equipment.RegardsHow to provide advice when your requirements a bit all over the place, meager, and "floating"?Based on what I seem to have understood as your requirements I'd pick the Siglent X (not X-E) out of those you listed. Simple reason: Not known for having significant flaws, specs seeming to meet your requirements and at about half the cost of the R&S one.Explanatory note: I consider Siglent to be a chinese "halfway A class" brand that is, I wouldn't (yet) put them next to western A brands like R&S. BUT: I guess we've all seen quite a few cases of A brands selling mediocre or somewhat flawed products.All in all I look at Siglent as a brand with, for China, good engineering and build quality, certainly good enough for a hobby or (not high-end) lab with a, for China, matching price that is, usually not among the cheapest chinese instruments but still significantly cheaper than comparable western brands.Side note: I (but that may be a personal thing) would absolutely not buy a multi-channel PSU without properly and fully independent/separate channels. I didn't check that yet for the Siglent PSU but definitely advise you to check that.Finally, yes, there are quite a few excellent western (good) brand PSUs which are within $ reach for you. Their main advantage IMO is that they are "battle-proved" and most of them are very well known here, have been torn down and analyzed, etc. and also often have schematics available. Their disadvantage is that buying second hand, e.g. from ebay, always carries some risk unless you buy from a very well reputed seller.All in all I personally would go that route (old, second hand) but one thing I'd certainly *not* consider: to buy a R&S PSU with a known, and known since years yet still not fixed (AFAIK) significant flaw. A Siglent PSU that meets my requirements I would, however, consider.

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2024, 12:53:36 am
content: Here is rigol dp932:edit: older R&S PSU I have also has a similar issue, but not as bad.

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 12:59:25 am
content: Quote from: nctnico on October 02, 2024, 08:27:40 pmThere are "certain" applications like motor startup, SMPS startup, and so on that require a significant startup current but this high current at Turn On shouldn't be "built-in" to the basic PS as a default setup parameter. This should be a user settable parameter either by a panel switch (old school) or modern UI Input.Remember long ago when a Power Designs (think this was the type) PS had a Turn Off glitch that cost us a couple $50K custom chip sets. When discovered we immediately took a hammer to the PS and returned it the "Calibration Dept"In Power Designs defense (or whoever it was), this wasn't a design defect, but a component failure, as we had many of these supplies in our lab and checked every one after this incident!!Best

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 08:24:45 am
content: The behaviour of the CC mode is even worse than I imagined. I did the following test: set the voltage to 8V, current to 10 mA, load is 50 Ohm. Image Scope_1 shows the transient when I hit the Output button on the NGE100. The first peak is almost 7.5V, so the current is appr. 150 mA. Then it remains stable at 120 mA for over 30 ms and then it decays to 20 mA (1V over 50 Ohm).Measured over a longer period, see image Scope_0, the current decays almost linear to 10 mA. This takes a whopping 12 seconds!!And finally, I attached a LED to the power supply. To no surprise, the LED did not survive.I will send all of this to R&S and see what they have to say. This behaviour is unacceptable for a reputable brand as R&S.@Anyone from R&S on this forum: feel free to comment...

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 08:29:36 am
content: Just for "fun", I set the Ramp time of the output to 0.1 s. That didn't help either.

author: pdenisowski
author_rank: Super Contributor
timestamp: October 03, 2024, 09:55:14 am
content: Quote from: mhsprang on October 03, 2024, 08:24:45 amThanks everyone for the posts and information. I've passed this on to our product management and R&D folks for power supplies and we're investigating. If you haven't already, please also submit this to your local technical support team and R&S account manager / distributor. I'll post updates as I have them.

author: pdenisowski
author_rank: Super Contributor
timestamp: October 03, 2024, 09:58:53 am
content: I'm also posting the relevant specificationshttps://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/service_support_30/NGE100_bro_en_5214-8748-12_v0101_96dpi.pdf

author: rsjsouza
author_rank: Super Contributor
timestamp: October 03, 2024, 01:03:57 pm
content: My Keysight E36312A has settings to delay the overcurrent protection "OCP Start" and "OCP Delay Start" - perhaps there is a similar configuration in the R&S supply that might be overloading the output?

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 01:16:56 pm
content: Quote from: rsjsouza on October 03, 2024, 01:03:57 pmThere is no such setting on the NGE100 series. Only a settable ramp up, which does not solve it. See reply #38 (four upwards).

author: rsjsouza
author_rank: Super Contributor
timestamp: October 03, 2024, 02:18:53 pm
content: Similar response on the E36312A with various settings(Edit to avoid confusion in the future) In this particular case, a 47 ohm resistor was placed in the output of channel 3 (set to 20V and 10mA). The curve was generated when the "output enable" button was pressed.Quote from: mawyatt on October 03, 2024, 12:28:36 am

author: blackdog
author_rank: Frequent Contributor
timestamp: October 03, 2024, 04:03:47 pm
content: Hi,Later this evening i will show some pictures of GW Instek, Rigol and Siglent power supply'smhsprangCan yo ushow us the puls responce @ 35mA please.Kind regards,Bram

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 04:20:12 pm
content: @blackdog: I can't before Monday when I'm back at the office. But I can tell you the response is the same up to about 140 mA. Above that, the first "plateau" is still there at around 130-140 mA but the curve rises afterwards.I can make some curves tonight from the PSU's I have at home: a small and cheap Tenma (< €100) and a somewhat larger TTi QL355P (€800-ish).

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 04:23:40 pm
content: Here's our GPP-4323 with same setup.Best

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 04:30:24 pm
content: showly charging the output capacitor

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 04:59:31 pm
content: Exactly, at the selected CC level.BTW this is an effective way to measure the Power Supply Effective Output Capacitance using:C = I/(dV/dT) in the linear rangeBest

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 03, 2024, 05:18:53 pm
content: Quote from: mawyatt on October 03, 2024, 12:28:36 amI don't disagree with that statement but this behavior is quite common for a number of supplies from reputable manufacturers.I just tested the supplies I currently have on the bench. All set to 8 V, 10 mA, loaded with 50 ohms. The attached pictures show the output voltage when the load is connected to the supply.HMP4040-E3646A.png: green trace: R&S HMP4040, white trace: Agilent E3646A.6632B.png: Agilent 6632B, with rear panel "Fast/Normal Operation" switch set to "normal" (notice the time scaling).The Agilent 6632B hangs at 8 V for about 150 ms.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 03, 2024, 05:34:58 pm
content: Keithley 2281Keithley 2281 with 100V/s slew limitR&S NGP800(Note the different vertical scale)Keithley 2461 (I mean, I'll burn their HQ if it didn't work properly)

author: mahi
author_rank: Regular Contributor
timestamp: October 03, 2024, 05:36:17 pm
content: Rohde & Schwarz HMP4040 (pre-facelift).Tested at 8V and 20V with 10 mA current limit in a 50 ohm load. Even at 32V the output looks the same as the 20V test.

author: 2N3055
author_rank: Super Contributor
timestamp: October 03, 2024, 05:43:55 pm
content: Quote from: rf-messkopf on October 03, 2024, 05:18:53 pmMaybe it is time we start reconsidering difference between good reputation and legends and lore..And assign brand value according to actual results and not "reputable brand" urban legends...

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 03, 2024, 05:56:24 pm
content: Quote from: 2N3055 on October 03, 2024, 05:43:55 pmTrue. Attached: same test with a 20 year old homemade supply, completely analog.Note: My tests show the load being connected to the supply, with the output already on.

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2024, 06:01:47 pm
content: Quote from: nctnico on October 02, 2024, 08:27:40 pmWith the 66311B "Mobile Communications DC Source" you could make the argument its not a general purpose PSU, so there will be trade-offs to optimize it for high speed response. I would argue a general purpose PSU should prioritize safety and stability over speed.Here is an old R&S DC source PSU (ngmo), same issue but much faster response:

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 06:44:05 pm
content: Quote from: rf-messkopf on October 03, 2024, 05:18:53 pmIf the output is enabled before you connect the load, you will obviously see a spike due to the capacitor on the output of the PSU. The idea is that you connect the load first, then enable the output. That is what I have been doing. And in that case, I think no overshoot should be tolerated.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 03, 2024, 06:56:46 pm
content: Quote from: mhsprang on October 03, 2024, 06:44:05 pmOkay, I thought you are after the transition from voltage to current regulation. Attached see the test with the output being switched on (green trace: HMP4040, white trace: Agilent E3646A), load is 50 ohms again.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 03, 2024, 07:43:02 pm
content: Here are the results from the power supplies I have at home. The Delta is a pure analog supply, the TTi is at least digitally controlled, has a keyboard and all, but I don't know of the control loop is analog or digital. The Tenma is also digitally controlled but cheap: €99. Setup is 8V, 10 mA in 50 Ohm. Load connected, then outputs enabled. Two screen shots each with different time bases, to see short term spikes and "long term" stabilisation of the set current.

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 08:00:51 pm
content: Quote from: mhsprang on October 03, 2024, 06:44:05 pmThat's what we've shown (with Blue LED as load), and agree on acceptable overshoot!!Best

author: nctnico
author_rank: Super Contributor
timestamp: October 03, 2024, 08:11:48 pm
content: Just to add another data point: The Keysight E36313A behaves OK. Set to 20V, 8mA with a 47 Ohm resistor attached.I had to use 500mV/div other wise the scope wouldn't trigger.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 03, 2024, 08:12:26 pm
content: Quote from: mawyatt on October 03, 2024, 08:00:51 pmSure, but still the settling time when transiting from voltage to current regulation varies among different supplies and can be rather long. The Agilent 6632B takes over 150 ms with a 50 ohms load, for example, as I show inthe post above. I find this rather disappointing. That will fry a LED instantly when connected to the supply when in CV mode with the output on. I should test that supply with the rear panel switch set to "fast".

author: 2N3055
author_rank: Super Contributor
timestamp: October 03, 2024, 08:51:24 pm
content: Quote from: rf-messkopf on October 03, 2024, 08:12:26 pmWell, that is mostly because of large capacitors on the output. To make it worse, internal impedance of capacitors is in milliohms...Current sources for testing sensitive devices usually have shorted outputs when you are connecting DUT, and you remove short to ramp up voltage/current in controlled manner. Current sources also can have voltage limiters, where you can set max voltage, and if current source is unloaded, limiters work like parallel regulators. Basically adjustable zener in paralel to DUT.Actually, that kind of device could be easily constructed and added as additional device in parallel to PSU output to "clamp" any misbehaviour....

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 03, 2024, 09:04:56 pm
content: Quote from: 2N3055 on October 03, 2024, 08:51:24 pmThe output voltage curve doesn't look like a discharging capacitor, though. Rather, the supply sits there for milliseconds before the voltage ramps down, same with the R&S, but much shorter. That's particularly unfortunate with the 6632B since it is a two-quadrant supply and can sink current up to the maximum rated output current.But I don't mean to hijack this thread as it is about a different topic.

author: blackdog
author_rank: Frequent Contributor
timestamp: October 03, 2024, 09:11:19 pm
content: Hi,As promised some measurements I made on LAB power supplies I own that have an enable key that are here on the test bench.Almost all measurements were made under the same conditions.Of the Agilent and the Siglent LAB power supply I have made additional measurements with in the case of the Siglent a higher current of 35ma and in the case of the Agilent I have increased the voltage and the current setting, this to investigate to what extent their behavior depends on the current setting.For convenience I have placed a picture of the LAB power supply under test in each picture.Basic settingsVoltage setting 8VCurrent 10mAThe power supply is switched on with the enable button.Two measurements per LAB power supply channel were taken using the single shot method on the scoop.This to get a better understanding of the power-on behavior of the LAB power supply.A Pk-Pk mA measurement is visible at the bottom left in yellow.Let's start with the Rigol DP832.First channel-1, but... that is R&S behavior.Let's zoom in on the horror..And now to channel-2 which, by the way, has the same characteristics and virtually the same peak current of about 25mA..And zoomed in again, that looks distinctly different from channel-1..Channel three of the Rigol can only deliver a maximum of 5.3V and the current is again set at 10mA..Hir is clearly visible that this channel behaves well, the peak current remains below 10mA..The following pictures are of a single channel Siglent LAB power supply and that is the SPD1305.This Siglent is not so kind to its load at this small current, 36mA peak current..Lets ZOOM in.It takes 30mSec for the current to drop to double the value of 20mA, you can do better Siglent!.I wanted to see if this Siglent Power Supply shows a different behavior at larger currents, below is a measurement at 35mA.At this 35mA, the behavior is much better..Only a small overshoot is visible and the abberations just after power-up are not significant..Now shall we go watch some more horror?WTF 130ms more than 160mA!.One positive is that the pulse is completely clean..Now let's see if at 200mA the behavior is below, I increased the voltage to 12V.There is comparatively less overshoot now, but, but.... 500msec long!.Now to the last one LAB power supply that behaves better and that is the GW Instek GPP4323.This Power Supply has four channels and channel one and two are the same so I am only showing channel one.Look R&S, Agilens and Rigol, this is how it should be..Immediately after turning on, a small abberation is visible but that is not important, the peak current remains below the set 10mA..This is a measurement performed on channel-4.Looks good..There are some abberations in the beginning, but the peak current remains below the set value..And now for the final measurements, still the GW Instek Power Supply and now channel-3.This channel can only deliver a maximum of 5.5V and that is what the measurements below were made with..A little hickup at the beginning, but well below the set peak current, no problemo, are you watching R&S, this is how it should be *grin*..From these measurements, it is clear to see that the “ current loop” of the GW Instek is a lot faster than the other Power Supply's I measured.Many of the Power Supply manufacturers make the current loop comparatively slow, then the power supply as a whole is easier to keep “stable”, but everything has its price, which is also visible in my measurements an from others in this topic.I hope to see more measurements from you!Greetings,Bram

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2024, 09:26:39 pm
content: Quote from: blackdog on October 03, 2024, 09:11:19 pmIts good that you measured current, probably should standardize on that.Peak of the first one was 25mA, R&S was 120mA, so not nearly as bad, IMO, but still not good.edit: Measured on DP832 and initial peak was only ever 18mA maximum with 50 ohm, regardless of current setting. So its only an issue if your current limit is sub ~15mA.

author: blackdog
author_rank: Frequent Contributor
timestamp: October 03, 2024, 09:38:52 pm
content: Hi thm_w ,I measured the voltage across a 50 Ohm resistor and set the scope channel to indicate the current value.I think it is all about not exceeding the set current and then it is more obvious that you indicate the current value on the scope image.That an LED can handle 2 or 4 times the maximum current for time “X” is not so important.Every LAB power supply is used for all kinds of other applications.My moral from almost 60 years of experience.I always test an LED with a series resistor.If I ever want to push some power into a battery, I always do it via a series diode.I don't like “fast”, I like to be careful and make sure that I don't break the d.u.t. I connect to a LAB power supply.Kind regards,Bram

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2024, 09:40:25 pm
content: Quote from: blackdog on October 03, 2024, 09:38:52 pmAgreed, updated my post.

author: Martin72
author_rank: Super Contributor
timestamp: October 03, 2024, 10:32:45 pm
content: Fast current control is a good thing for sensitive components if you want to connect them directly to the power supply.However, there are situations where this is rather counterproductive.Certain DC/DC converter circuits have an inrush current that can easily be many times the normal input current.If this is not taken into account when switching on, it can, at best, lead to non-functioning without side effects, but in some cases it can lead to permanent current flow, causing the circuit to “hang”.As always, the dose makes the poison.However, I also prefer series resistors for LEDs, it's just in my nature...

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 04, 2024, 12:16:41 am
content: Quote from: Martin72 on October 03, 2024, 10:32:45 pmThe delayed switchover from CV to CC mode, where the supply sits there for a few milliseconds before an exponential ramp down is seen (as expected for a capacitor discharged through a resistor), might actually be implemented on purpose. This delay might also be responsible for the overshoot that is seen when the output is switched on with the enable button with a load connected.The current control loop itself seems to be much faster. Attached is the result of the following experiment: Supply (R&S HMP4040) is set to 8 V, 150 mA, output on, and loaded with a 50 ohms resistor (i.e., it is in CC mode with 7.5 V at the output). Then an additional 4.7 ohms resistor is switched in parallel to the 50 ohms (i.e., output voltage should jump down to 0.64 V). The transition takes about 1.7 ms (from 90% to 10%) and looks exponential as expected for a cap discharged through a resistor, with no obvious delay before the exponential decrease.Maybe R&S can comment on this behavior.If it is intentional, it would be nice if the user had control over it, though.Edit:Repeated the same measurement, but with the 4.7 ohms resistor switched in by a MOSFET in order to demonstrate that there is no appreciable delay between switching and supply response. Lower trace is the gate drive pulse.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 04, 2024, 12:58:58 am
content: Quote from: blackdog on October 03, 2024, 09:11:19 pmWhat probe were you using to do these measurements?Thanks,Josh

author: moerm
author_rank: Regular Contributor
timestamp: October 04, 2024, 02:11:00 am
content: Quote from: 2N3055 on October 03, 2024, 05:43:55 pmI logged in specifically and just to thank you for that.But being logged in anyway ...Quote from: Martin72 on October 03, 2024, 10:32:45 pmI get it but let me play a bit Cassandra ...With a *linear* *lab* PSU my main concern is potentiallysensiblestuff (being powered). You are right, there are exceptions and corner cases in almost everything which leads to a need for deciding for priorities (mine I just told). Besides switchers tend to care little about the quality of input power, many circuits however *do* care.Some of my - almost all self designed and built - PSUs do have a "don't limit (DUT) inrush current for 3 or 10 ms (selectable) with a 0 ms option (~no tolerance, strictly stick to the set current limit)" feature and most of them have a separate "emergency brake" set to double the set current limit (max the highest output current of that supply). Reason: a supply should be "generous and tolerant" but not to the point of getting damaged itself.What I've seen here (thanks guys!) would have been, had I known it (I didn't) yet another reason to design and build my PSUs myself rather than buying "well known brands". I'm not really surprised though that "famous A-tier brands" sell what I call crap; maybe my wording is a bit harsh but "A tier brand" quality certainly is not what I see here (modulo one "B-tier" brand).Whatever, thanks for all the data (and nice images *g).

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 04, 2024, 03:31:26 am
content: Quote from: pdenisowski on October 04, 2024, 01:28:11 amPersonally I'm not exactly sure since it is tricky to figure out which specifications override what, and whether those interrelated specifications should be interpreted strictly ("any" exceed) or loosely ("all" exceed).For example, if we take my NGP800 load current regulation spec strictly (< 0.01% + 5mA) then my peak result of 160mA inrush at startup is well beyond the allowable spec range of 10mA * 0.01% + 5mA, which basically allows for 15.001mA max inrush.The inrush duration is also well beyond "Load recovery time" spec of 400µs, so can't use that either to handwave.NGP800 does not specify CV-to-CC transition time. Is this the "get out of jail free" card?Fuse delay time *may* allow this, but that's protection function while the discussed performance should be regulation function. And sure enough if I set the fuse to protect close to the setpoint (20mA) it did indeed trip on itself during startup. Job well done there.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 04, 2024, 07:53:54 am
content: Quote from: Martin72 on October 03, 2024, 10:32:45 pmAgreed on inrush currents, but those will be obvious if you switch on the power.But that is not the point of all of this. If we set a voltage on our PSU, we expect that PSU to output that voltage, no more. Similarly, if we set a current, we expect that PSU to output that current, no more. If a manufacturer specifies that a set current may be +/-5% + 5 mA, I do not expect the output current to be 14 times higher than that. And if the design shows transients at enabling the output, I want to see that beforehand in the datasheet and not after the purchase on my bench.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 04, 2024, 08:02:15 am
content: Quote from: pdenisowski on October 04, 2024, 01:28:11 amYes, I sent an email to R&S support yesterday about this.And yes, I feel this is outside the specifications for exactly the reasons ArdWar just stated in his reply #73, just above.

author: blackdog
author_rank: Frequent Contributor
timestamp: October 04, 2024, 01:26:34 pm
content: Hi, :-)KungFuJosh asked for some explanation of what scope probe I was using, which can be seen below in the picture.Cost about 1850$ *grin*The comment above is a hint to the major measuring instrument manufacturers who regularly charge outrageous prices for all kinds of probes.Probing setupThe tests I did with current limiting around 10mA required a 50 Ohm resistor and about 1-Watt.I used 2x a 100 Ohm resistor in parallel with a 1M Banana Crock cable from GW Instek and to the scope I used one 1M BNC to Crock cable.One and all can be seen in the photo below.I have been thinking about running the measurement setup “HF”.But on reflection this was not really necessary, this because the LAB power supplies tested have between 100uF and 680uF across the terminals.This does not allow fast rise times in the measurements.I use two already older scope probes on my test benches from Micsig for commonmode measurements and current measurements, which are the DP10007 and the CD2100B.For my work these probes are satisfactory and they are very affordable.But Micsig also has faster probes available and still affordable prices.In my measurements, however, these Micsig probes have not been necessary, K.I.S. was a good mindset here, so i used basic cables.First the picturesThe used probe.Scoop setupIn this photo, I left the settings for channel-1 on, so it is easy to see what I worked with.CouplingThe coupling is DCBandwidthBandwidth is 20MHz, otherwise too much noise is visible.These measurements are about waveform and level and not because I want to see everything that happens while measuring.I do always start with the “window wide open” when making measurements.Then I have an impression if there are things that also come into play that I need to take into account.PressentationMost measurements I show on forums are “without” noise, so that the attention goes as much as possible to the measured signal of interest.Scale factorSo the next setting is the scale of the channel used, and this is set by using the “User1” setting of the Siglent scope.Here the setting is 50V per ampere.Input impedanceThis should be set to 1M Ohm so as not to blow up your scope.UnitThis should be set to Ampere unit, this because we are measuring the peak current behavior of a LAB power supply..And now for some comments on LAB Power Supply's.I've tested a lot of different circuits and I've developed a fondness for the “Harrison Consept.”That is that the reference section has its own floating power supply and the control current for the power section usually comes from a current source.Then there are two control loops one for current and the other for voltage.Which then control the current through two diodes to the Power section.Nowadays it is a whole lot easier to make a fast responding LAB Power Supply.The advantage is that it is then possible to keep the capacitor across the output terminals low and still have a fast responding loops with good dynamic behavior.This has not yet caught on with many manufacturers,a thick capacitor across the output terminals and slow opamp/power transistors is much cheaper.Better loop contro en component choicesFurthermore, a current source that always draws current from the output(when the channel is turned on) helps well for excellent dynamic behavior.There are also opamps available these days that have a large phase and gain margin, look at the ADA4625 models from Analog Devices.This opamp series has low noise, little bias current, fast and little offset, but above all a phase margin of 88 Degrees at 100pF capacitive load, which is excellent!Everything I have written here is mine no AI, but translated by deepl.comAnd I'm a dyslexic Monkey, which can lead to pretty crooked sentences.Kind regards,BramEdit picture

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 04, 2024, 03:07:59 pm
content: Quote from: ArdWar on October 04, 2024, 03:31:26 amThat spec exclusively refers to the voltage regulator. A 'normal' bench PSU with a single series pass regulator is unable to sink current. Thus, when in CC mode and the load resistance drops so that the supply has to lower the output voltage in order to keep the current constant, the excess charge in the fixed output capacitor corresponding to the voltage difference has to be dumped into the load. The supply cannot take up this charge. Therefore, we see the exponential decrease of the output voltage shown a number of times in this thread, and this decrease will depend on the load. There is no way around that, unless the PSU is a two-quadrant one like the Agilent 6632B which can down-program the current, or a SMU.Quote from: mhsprang on October 04, 2024, 07:53:54 amWell, transients exceeding set values are inevitable when the load resistor suddenly drops in CC mode, as the normal bench PSU cannot sink current, and the transition time will be load-dependent.The delay time when transitioning between CV and CC mode (I'm not aware of a PSU that actually specifies that delay) is another story. I can see why they seem to be doing that. Otherwise you can get rapid oscillations between CV and CC mode. I've run into that with homebrew PSU designs and complex nonlinear loads long time ago. The question is which delay is appropriate. I think the approx. 150 ms of the Agilent are a bit too long. Would be nice to have control over it, and to have it specified at least.Quote from: mhsprang on October 04, 2024, 07:53:54 amThat overshoot when the supply is activated with the output enable button and with a load connected which draws more current than set is yet another story. I agree that I'd prefer the supply not actually doing that. But one may also argue that it should behave just the same way at startup as when transitioning to CC mode in order to deal with complicated loads. Again, I'd prefer user control over this behavior.So no idea whether this is in spec or not.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 04, 2024, 03:19:37 pm
content: Quote from: blackdog on October 04, 2024, 01:26:34 pmThank you for all the details!Also... Damn it! I knew it was going to be an expensive probe. 😉

author: jayk
author_rank: Regular Contributor
timestamp: October 04, 2024, 04:14:55 pm
content: All this is making me feel a lot better about my GPP-4323. If only it had a decent web interface and were a bit quieter under load it would be perfect. Still a great value for the money.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 04, 2024, 04:21:57 pm
content: Quote from: rf-messkopf on October 04, 2024, 03:07:59 pmIf you go back and take a look at reply #37, second image, you see the current spike first, then drop from 20 mA to 10 mA (setpoint) in several steps over a period of12 seconds. That has nothing to do with any capacitor discharge but everything with something that goes terrible wrong in the firmware.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 04, 2024, 04:37:28 pm
content: Quote from: mhsprang on October 04, 2024, 04:21:57 pmAgreed, that should definitely not happen and is out of the setting accuracy spec. R&S should fix that.I have not seen something similar on the HMP4040 or any Agilent supply, though.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2024, 07:42:40 pm
content: I think you need to define it differently. An ideal current limited power supply has two control loops running at the same time: one loop regulates the output so the set current limit isn't exceeded, the other loop regulates the output so the set output voltage is not exceeded. And this should be an AND function. Set current AND set voltage should not be exceeded.From the graphs it looks like that in some power supplies the current limit control loop is disabled for a short while causing the output to be regulated to the set voltage but ignoring the requirement for the current limit.I don't think this is a matter of specification but the very basic behaviour of a lab power supply. The set current limit and set voltage should never be exceeded under any circumstance as this will cause damage to devices connected to the power supply; hence there is no need to specify this.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 04, 2024, 07:58:52 pm
content: @pdenisowski: Although I am an electronics engineer, I am also a "user". So, if I purchase a power supply with CV and CC capablities, then to my circuit I design I am the engineer but to the power supply I am "merely" the user. In my opinion, I do not need to get to understand how my power supply works, based on assumptions and experiments. Instead, I rely on its specifications in the datasheet.If I set it to be used as a current source with a certain max. voltage, I may expect, as a user, that those setpoints are honoured. I don't care about control loops and arguments about how the V and I loops interact, I only care that if I set the max current to be 10 mA, that the current will not exceed 10 mA. I will accept that there is a large capacitor at the output terminals, and that is why I use the "output enable" button to enable the power, instead of plugging in the cables to my delicate circuit,assumingthe output cap is after the switch. Even this should be in the specifications, IMO.To come back to my example in reply #37: I connected the 50 Ohm resistor to the power supply, which was set to 8V and 10 mA. I enabled the power to the resistor by pressing the Output button on the NGE100 while the resitor was connected already. So from that point onwards, it is the power supply's responsibility to deliver what I asked it to: 10 mA of current with a max. voltage of 8V. Then I hit the output button, as a user.Seeing the current overshoot to 140 mA for 30 ms is one thing, althoug it exceeds the 200 us in the specs, but seeing the current drop from 20 mA to the setpoint of 10 mA over 12 seconds is a blatant violation of the specifications of this power supply. One could also say: I did not change the load. I merely enabled the output to a constant load.

author: blackdog
author_rank: Frequent Contributor
timestamp: October 04, 2024, 08:09:27 pm
content: Hi pdenisowski, :-)I have a suspicion that you don't understand what test was done....PreparationSet a LAB Power Supply to 8V and set the current to max 10mA.Now connect a 50 Ohm resistor across the output terminals of the channel you set.Connect a scope across the 50 Ohm resistor.Set the scope to say 100ms time base time and single shot and the trigger level to say 30% of the expected value.If you want to do it nicely, set the scope for your used channel to current measurement and then adjust the sensitivity in the probe settings to 50V/A.Now the peak current is neatly readable on the scope screen.Connect the scope with a BNC-Crock cable 1:1 low cost probe, as in my previous photo.If everything is set up correctly and you turn on the LAB Power Supply via the enable switch, you will see the behavior of the Power Supply you are testing.The maximum value of the current through the 50 Ohm resistor should not exceed 10mA.This above is a good test for the behavior of the I-Loop control.This test is slightly different from the test for the dynamic Voltage behavior of a LAB Power Supply.In this, you vary the load current over a short period of time and see how well the LAB power supply responds in terms of the U-Loop.Many manufacturers specify from 50 to 90 or 100% load, and there are some that test 10% to 100% as a test in this dynamic U-Loop test for e.g. within 50uSec within a few mV of the set voltage value.By the way, these are just two of the tests you can do on LAB Power supplies dynamic behavior.Like this measurement which I also think is important, i have never seen a manufacturer specify how much commonmode interference comes out of a LAB Power supply output.Especially the ones that have switching behavior, linear post-regulation usually doesn't help with that.But let me not digress, the current test at issue here shows nicely what a manufacturer thinks is important,my measurements of a few LAB Power Supply's shows that fast current control at the GW Instek Power Supply is well taken care of.I hope things are more clear now.Kind regards,Bram

author: mawyatt
author_rank: Super Contributor
timestamp: October 04, 2024, 10:14:02 pm
content: Think most users work with a Lab Supply the way Bram describes, and this is also how we generally utilize a Lab Supply, especially when sensitive circuits are involved.The Power Supply is Mains Powered On, Voltage and Current Limits are set, the DUT is connected either before or after the Limits set, then the PS is Enabled turning ON the Output(s).In this use case the Power Supply should not overshoot the Voltage or Current Limits set by the user IMO.Some Lab Supplies like the GPP4323 and SPD3303X have an ALL ON/OFF Single Button to Toggle the Outputs ON and OFF which hints at the above described use case. This is a nice feature when one is utilizing multiple outputs which is common with complex DUT circuits/systems.Best,

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 04, 2024, 10:32:26 pm
content: I did blackdog's test with my SPD3303X v6.2 hw.For values set below 30mA, there's a spike to nearly 30mA before dropping to the set current. For currents 30mA and up, there's no overshoot.Inserting the probe into the scope was seen as nearly 15mA.

author: Martin72
author_rank: Super Contributor
timestamp: October 04, 2024, 10:53:21 pm
content: QuoteThis is the point that should be internalized.If you set the current limit of a power supply to 30mA, for example, this is no different than setting a controller setpoint.If you then enable the output and allow current to flow, it takes a certain amount of time for the actual value to match the setpoint.This is the nature of the controller.You cannot expect the current to be limited “instantaneously”.

author: thm_w
author_rank: Super Contributor
timestamp: October 04, 2024, 11:41:51 pm
content: Quote from: Martin72 on October 04, 2024, 10:53:21 pmSeems beside the point when we already have demonstrated supplies that do not overshoot, and that is the desired behavior.

author: 2N3055
author_rank: Super Contributor
timestamp: October 04, 2024, 11:52:42 pm
content: Quote from: pdenisowski on October 04, 2024, 10:37:07 pmI wanted to stay out of this discussion but am getting an itch..Paul, this is not moment for clever lawyer talk that "technically" specifications are not violated because someone in R&S used clever wording in datasheet...Current limit is exactly that: a limiter that limits that current does not exceed set current limit. You can accomplish it with some kind of electronic fuse that will disconnect load, you can enable foldback limiting (that will reduce current to minimal until you reconnect load) or you can enable constant current mode that will keep constant current.In any case, current should not exceed the set limit. It is a limit, not some general recommendation.If one wants to be able to deal with difficult loads that have large startup current, than that has to be separate, configurable option.Those are, generally speaking, expectations form average user.And when they pay 3x the money (or 10x) they expect it behave better that some cheap PSU.Which here is not the case, because I have Rigol DP831 that behaves very well in this overshoot test, and to add insult to injury, I have two noname analog PSU that are even better in that regard, behaving like decent current source when starting. They also switch between voltage and current control loops without much saturation in error amplifiers, making transition quite smooth.I refuse to believe R&S cannot make it better than some noname small manufacture in China copying 50 year old HP design.But maybe design dept and product leaders should pay more attention to analog design that to "visual identity of the brand".R&S is brand that is famous for their outstanding devices with state of the art performance.It is not Versace. Or Apple. Or some luxury brand that sells and designs something that is fancy and status symbol but not mean to be really pushed to the limit.R&S is not supposed to be Vertu encrusted in diamonds but basically just an ordinary phone.R&S is supposed to be state of the art military communication device with state of the art performance.More like LeMans Porsche LMP race car than Porsche SUV with leather seats.

author: Martin72
author_rank: Super Contributor
timestamp: October 05, 2024, 12:02:29 am
content: Quote from: thm_w on October 04, 2024, 11:41:51 pmThen they have a very, very fast controller.You have to reach the point where you have to cut back, in any case, time passes for that.

author: 2N3055
author_rank: Super Contributor
timestamp: October 05, 2024, 12:03:57 am
content: I actually looked into user manual.It explicitly states that PSU functions in Constant Voltage (CV) or Constant Current (CC) mode.

author: thm_w
author_rank: Super Contributor
timestamp: October 05, 2024, 01:22:25 am
content: Quote from: Martin72 on October 05, 2024, 12:02:29 amThe other test that could be done is to compare the speed of regulation once the output is on, though at low currents like this its complicated by the size of the output capacitor.Maybe that would tell us if it is a regulation loop speed issue or simply a software bug (timing or sequencing of the output)?

author: rf-messkopf
author_rank: Regular Contributor
timestamp: October 05, 2024, 01:41:55 am
content: Quote from: pdenisowski on October 04, 2024, 10:37:07 pmAs has already been remarked by others, there are supplies which do not behave in this way. They seem to ramp up the voltage slow enough when activated by the output enable button for the current control loop to prevent an overshoot.However, it is true that when a load is connected to an already activated PSU channel set to a certain voltage, and if the load will draw more current than set, then the current will necessarily overshoot. A number of supplies (among them R&S) seem to wait a couple of milliseconds before switching to CC and the current controller actually starts to ramp down the voltage in order to regulate the current. As I wrote before (seethe post above), this behavior could be designed in deliberately.Also, we speculated that it could be this delay that makes the R&S supplies (among others like the Agilent 6632B) overshoot when activated by the output enable button with a load connected that will draw more current than set. There may be pros and cons for this behavior. I'd prefer no overshoot, or user control over the delay when transitioning between CV and CC mode.Besides this overshoot (which may be intentional), user mhsprang has seen an issue with the settling time to the set current value in CC mode. To understand this issue one has to realize that a 'normal' bench PSU with a single series pass regulator cannot sink current. Thus, when in CC mode and when the supply has to lower the output voltage to keep the current constant, the excess charge corresponding to the voltage differential in the fixed output capacitor has to be dumped into the load. Therefore, with a resistive load an exponential decrease of the output voltage is expected and has been seen a number of times in this thread. Also, the settling time will depend on the load. There is no way around that, unless the PSU is a two-quadrant one like the Agilent 6632B which can down-program the current, or a SMU. Therefore the settling time spec of normal bench PSUs only refers to the voltage controller. I've never seen a current settling time spec for CC mode.Now mhsprang has noticed the following: He connects a 50 ohms load to his NGE100 (set to 8V, 10 mA). Then there is the (deliberate?) delay of about 40 ms before the current controller becomes active. Then there is the expected exponential voltage decrease due to the output capacitor (approx. 50 ms). But then it takes another whopping 12 seconds before the output current actually reaches the set 10 mA. Take a look again at the diagrams in post #37. The vertical scale is in volts, but notice that due to the 50 ohms resistor across the output, it is proportional to output current. After the exponential decrease is over, the output sits at 1 V (i.e. 20 mA) and slowly ramps down to 0.5 V (i.e. 10 mA) within 12 s. There is a clear distinction between the exponential part of the curve and the slow ramp to the set current.Even though there is only a setting accuracy spec for the current controller (0.1% + 5 mA, so the 20 mA are way out of spec) and no settling time specified (as explained before, there can't be because it depends on the load), I think it is unacceptable for a PSU to take so long before a set value is reached.I hope this makes things clearer.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 05, 2024, 09:22:14 am
content: Quote from: pdenisowski on October 04, 2024, 10:37:07 pmWell, exactly. I configure a current limit. So I don't expect the current to exceed that limit.Quote from: pdenisowski on October 04, 2024, 10:37:07 pmThe power supply "knows" that it is going to deliver voltage and current because I press theOutputbutton. So, the firmware could, instead of outputting 10V at once, slowly ramp up the output voltage until the current limit is detected. And this ramp up only needs to be slow enough for the control loop to keep up.Also, I have built many current source circuits in my life and none of them have ever fried LED's. This implies that one can certainly design a power supply in such a way that the software drives hardware voltage and current sources by means of reference voltages output by DACs, where the actual control loop exists in hardware.If your control loop is enterely in software, it is also very well possible to behave correctly in my opinion. And if I had loads of spare time, this thread alone is enough motivation for me to design such a power supply with all this in mind.Quote from: pdenisowski on October 04, 2024, 10:37:07 pmThe load was a 50 Ohm resistor. So, if the current dropped from 20 mA to 10 mA over 12 seconds, the voltage (that was actually measured on the scope), dropped from 1 V to 0.5 V over the same 12 seconds. Ohm's law...

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 05, 2024, 09:41:23 am
content: I´ve often seen this behaviour on pure SMPS. They often have an analogue control loop only for the voltage, but constant current mode is then realized in software and so it takes a relatively long time to switch over. This is okay for charging batteries, but not for anything that needs CC-mode to survive.Also old-style linear PS often have a much slower control loop for CC than for CV to prevent oscillations with inductive loads.But I completely understand that you expect from a premium-priced lab PS to well perform in this area. Even with SMPS it´s possible to post-regulate the output with a linear regulator that quickly reacts to load changes. It´s no magic to do this within ms, and it´s no magic to define a ramp-up that prevents overshooting.

author: mawyatt
author_rank: Super Contributor
timestamp: October 05, 2024, 04:22:21 pm
content: This thread is an important message for even older more seasoned folks in that it illustrates the Power Supply is not near a source with ideal behavior, especially true wrt to Voltage and Current Limits and how they operate.When dealing with sensitive circuits consider setting the PS Current Limit slightly above the normal operating current, which of course slows the voltage ramp up time (decoupling capacitance) and usually isn't a problem. However some circuits require a high inrush which must be dealt with as needed, here we usually set the Current Limit to above the inrush or at a level where the circuit starts up properly after turning the supply ON, then manually reducing Current Limit to slightly above normal operating current.This is a learned behavior, as we've smoked our share of circuits and components over the past 65 yearsAnyway, this thread has been enlightening, delving into some PS behavior that most folks should find useful.....and it hasn't turned into apissingcontest......yetBest,

author: Thomas
author_rank: Regular Contributor
timestamp: October 05, 2024, 05:38:22 pm
content: That Agilent 6630B is something special.A 100W power supply in a 2U 19" box weighing 15kg - one would expect it to perform damn near perfect.Anyway, I checked my supplies too - not so exciting, except for one.My TTi EL302RT is made with potentiometers, LM324s and 2N3055s - basic, oldschool and budget friendly.Note the time scale - this thing is fast. Nice.

author: blackdog
author_rank: Frequent Contributor
timestamp: October 05, 2024, 06:20:41 pm
content: Hi,My Power Supply weekend preachingand all my opinionI think this topic is important, that's why I put time into it to explain a few things.1The power-on behavior of a LAB Power Supply is just one of the important features.2A second is the overload behavior when the current exceeds the set value.3Then we also have the behavior of the power supply when the output is shorted.I have done quite a few measurements on LAB Power Supply's and that was often shocked by the very high peak currents.Of course this is not just because of the capacitor across the output terminals, besides this short peak current you also have the peak current due to the often much too slow regulating current loop.4And then again how well does the U-loop react when the current reaches its normal value again.5Some problems can be solved by what I indicated earlier by using a current source that always draws some current from the power section.Yes, that takes some energy, but you get a much better U and I loop from it, the power section then always remains well in its operating range.6It is unfortunate that a number of manufacturers are moving more and more to software-controlled U and I loops.This usually does not improve the quality and especially not if the U and I loop is realy done by a ADC and the processor itself.No hair on my head thinks about such a modern LAB Power Supply here on my workbench.My experience with modern measuring equipment and software bugs is not really positive....7Many people who start with electronics often make a bench power supply, often because they think it is easy, many simple schemas are available through search engines.9I am too old to have done that via search engines, with me they were magazines of course. :-)Many power transistors I have blown and so I learned that a linear power supply is anything but simple.Almost no construction project mentions the phase margin for the U and I loop.Nowadays this is a lot better, but especially for the SMPS types and their configuration.9On many forums when one is asked for help to decide regarding power supplies, often the first reaction of forum members is that an SMPS type should be used and this is Wrong, Wrong, Wrong!That usually indicates that the ones proposing that have little measured equipment with SMPS power supplies.For those who are going to build something themselves with SMPS, they are then stuck with a very big EMC/common mode problem.Then when I counter, the comments often come that in my scope, phone are also SMPS power Supplies and that is correct.These are often very well designed and tested for EMC and I don't see the average homebuilder replicating this....10But the manufacturers of all kinds of equipment can also do something about EMC interference and common mode problems.I have several function generators here that inject EMC into my D.U.T. with their SMPS Power Supply.For this I bought a Scoop/Function generator model from OWON that runs on battery.And gone are my commonmode problems with certain measurements.More and more I have to turn off equipment on my main workbench to do measurements at low levels.I now have a second workbench with less equipment and where almost everything is off (real power switch), so no equipment with Standby Power Supply's etc.And then consider how I think about a Power Supply that has a switching pre-regulation and then a linear post-regulation.Then you're still stuck with the commonmode injection of the switching part, yea... but not on my measuring bench...This is a personal opinion.11Above all, don't get me wrong, I am very happy with the SMPS technique but it is certainly not the holy grail.That technique also has major negative characteristics.What you are going to apply must be looked at holistically in my opinion.What is needed, what is stable, how much power loss may occur, what are the error situations that may occur and how much EMC is permissible and of course the cost.12There is no “One Size Fits All” LAB Power Supply.But for an electronic lab, you do expect it to be “clean” with both a fast U and a fast I loop and otherwise no on or off abberations of the Power switch and or the enable key.13The last one!A LAB power Supply must be kind to itself and to the D.U.T that is connected to, this is perhaps the most important premise...Kind regards,Bram

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 05, 2024, 06:24:49 pm
content: Quote from: Thomas on October 05, 2024, 05:38:22 pmHow the heck did they fit a person into a PSU?!?!?! 🤯🤯🤯

author: 2N3055
author_rank: Super Contributor
timestamp: October 05, 2024, 07:39:00 pm
content: Quote from: KungFuJosh on October 05, 2024, 06:24:49 pmIt is tight. But hey man has to put food on the table..

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 05, 2024, 08:29:39 pm
content: Quote from: 2N3055 on October 05, 2024, 07:39:00 pm🤣🤣🤣

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 11:33:14 am
content: Some tests regarding Siglent SPD4000X series starting athttps://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5666851/#msg5666851

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 01:50:37 pm
content: See new related thread.https://www.eevblog.com/forum/testgear/lab-power-supply-turn-on-and-off-characteristics/Best

author: glitchcatcher
author_rank: Contributor
timestamp: October 12, 2024, 10:50:53 pm
content: Quote from: thm_w on October 03, 2024, 06:01:47 pmIt looks like the industry disagrees on thatFrom R&S document "Fundamentals of DC Power supplies – output characteristics":

author: salomonander
author_rank: Regular Contributor
timestamp: October 13, 2024, 11:01:20 am
content: This is a bit disappointing. Im still set on buying an NGA102 as the problem wont bother me much in my applications. But after i saw Daves video where he showed this issue and studying the firmware notes i was convinced that they have tackled the issue. They are well aware of it. See the firmware notes:https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/pdm/firmware/5601_9009_00/NGA100_ReleaseNotes~1.pdfDoes anyone here have a NGA100 with up to date firmware who can comment?

author: pdenisowski
author_rank: Super Contributor
timestamp: October 14, 2024, 08:21:24 am
content: Quote from: salomonander on October 13, 2024, 11:01:20 amHere's the output of the NGA142 connected to a 50 ohm load

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 14, 2024, 04:19:07 pm
content: Quote from: pdenisowski on October 14, 2024, 08:21:24 amCan you do some more tests that put that in the context of the other tests that have been done? For example:https://www.eevblog.com/forum/testgear/lab-power-supply-turn-on-and-off-characteristics/msg5667833/#msg5667833I would like to see current response also, not just voltage.Thanks,Josh

author: mhsprang
author_rank: Regular Contributor
timestamp: October 14, 2024, 04:22:06 pm
content: Quote from: KungFuJosh on October 14, 2024, 04:19:07 pmThatisthe current response. The oscilloscope shows that the voltage doesn't rise above 40 mA * 50 Ohm. And since this is a resistor, the current flow is idential in "shape" as the voltage across the resistor.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 14, 2024, 04:31:49 pm
content: Quote from: mhsprang on October 14, 2024, 04:22:06 pmGood point. I guess I was thrown off by how pretty it looks. I guess the OP really does need an R&S. 😉But also, I'm curious about lower current settings too. For example, setting a 10mA or 20mA current level. Some PSUs behave differently depending on the current setting.For example, my SPD3303X only overshoots when set below 30mA, as 29mA is the typical overshoot on power activation.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 14, 2024, 05:09:12 pm
content: @KungFuJosh,I agree about the lower current setting. I sort of started this by observing a huge overshoot on my R&S NGE103, which is now being investigated by R&S. That overshoot is happening at all currents below 140 mA and is always up to 140 mA.So, maybe this NGA 142 is doing allright at 40 mA but behaving bad at 10 mA. Maybe @pdenisowski could repeat this test at 10 mA as well.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 14, 2024, 05:23:14 pm
content: Quote from: mhsprang on October 14, 2024, 05:09:12 pmUh oh, don't let R&S know my little Siglent PSU is behaving better than their PSU that costs 3 times as much. Or maybe that will get them to fix it faster. 😉😉

author: mhsprang
author_rank: Regular Contributor
timestamp: October 14, 2024, 06:45:57 pm
content: Quote from: KungFuJosh on October 14, 2024, 05:23:14 pmThey already know that

author: pdenisowski
author_rank: Super Contributor
timestamp: October 14, 2024, 07:37:47 pm
content: Quote from: mhsprang on October 14, 2024, 05:09:12 pmI'll have to borrow another NGA to test against, but the NGA is a purely linear power supply, so I expect something very similar.

author: salomonander
author_rank: Regular Contributor
timestamp: October 16, 2024, 12:34:34 pm
content: Do these spikes in current mode only happen with number small number below 20-30mA? Or does it also happen when i limit it to say 60mA? Thanks

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 16, 2024, 05:00:54 pm
content: Quote from: salomonander on October 16, 2024, 12:34:34 pmThat depends entirely on the brand/model of PSU. My Siglent SPD3303X only spikes up to ~29mA, so anything below that will see more current for a very short spike before dropping and then going up to the current setting. For anything over 30mA it doesn't matter since the spike hasn't ever gone above that in my tests.Different brands have shown different results. Some much better, some much worse.