Lab Power Supply Turn ON and OFF Characteristics - Page 1
Forum section: electronics / testgear

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 01:40:11 pm
content: Since there's been some discussions on various Lab Power Supply Turn ON and OFF misbehavior, thought a thread dedicated to such might be in order.https://www.eevblog.com/forum/testgear/power-supply-for-home-lab-do-i-really-need-a-rs/First off, think creating a setup and parameters that can be utilized for comparisons is necessary, so we'll start off with aproposed setupfor evaluating the Turn ON and OFF characteristics.1 ) Use 50Ω Load Resistor (usually available to everyone as a discrete resistor, or BNC termination type, or directly within the DSO).2 ) Use General Purpose 10X DSO probe.3 ) Use 20MHz DSO Bandwidth limit.4 ) Set Power Supply Voltage to 8V.5 ) Set Power Supply Current Limit to 40mA.6 ) Set DSO to 0.5V/Div for full scale with 4V.7 ) Trigger DSO on Rising Edge Single Shot for Turn ON Behavior (Falling Edge for Turn OFF Behavior)8 ) Use Power Supply Enable ON/OFF to activate the output.9 ) Capture DSO waveforms at various Time Scales starting with 50ms/Div, add additional Time Scales and identify such to show more details such as fast initial glitch (100us/Div) and slow settling (200ms/Div).10 ) Annotate waveform displays with details.11 ) Main purpose is to show Voltage/Current Overshoot (if any) at Lab Supply Turn ON and Turn OFF.Voltage/Currrent overshoot at Turn ON and/or OFF is our main concern with a Lab Supply, others may have additional concerns, but for now let's stay focused on the Turn ON/OFF Supply behavior.Hopefully this will yield a means to compare various Power Supply characteristics with a more uniform test procedure/parameter setup.Anyway, comments, recommendations, additions welcome with goal to yield a set ofexpertagreed upon setup and test parameters to allow various Lab PS evaluations.Best

author: Kleinstein
author_rank: Super Contributor
timestamp: October 06, 2024, 02:29:19 pm
content: With a 8 V supply and possibly higher it is not a good idea to use the scope internal 50 ohms. Depending on the scope this may already be damaging from overload, especially over longer time.The transients from a lab supply are usually slow enough that the exact probing ( 1:1 or 1:10 probe or Z0 probe) does not matter. The load may make a small difference.8 V and 50 ohm would be 160 mA. So a setting to 40 mA would have the supply in CC mode.So one would more tend towards a high load resistor (e.g. 100 or 220 ohm) and a slightly higher current limit like 100 mA or 500 mA.Not so sure why 8 V. More relevant may be 5 V or 3.3 V as a supply to quite some low voltage circuits that may care about an overshoot.

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2024, 02:38:58 pm
content: Quote from: Kleinstein on October 06, 2024, 02:29:19 pmAgreed. For simplicity, a 47 Ohm resistor might be a better choice as this is a standard E12 series value

author: Fungus
author_rank: Super Contributor
timestamp: October 06, 2024, 02:54:33 pm
content: Quote from: Kleinstein on October 06, 2024, 02:29:19 pm"5) Power Supply Current Limit to 40mA"But yeah, a 47 Ohm resister seems more sensible.

author: Fungus
author_rank: Super Contributor
timestamp: October 06, 2024, 02:59:06 pm
content: Quote from: Kleinstein on October 06, 2024, 02:29:19 pmThis, too.

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2024, 03:18:48 pm
content: Quote from: Kleinstein on October 06, 2024, 02:29:19 pmThis is exactly the purpose of this thread. See the last few pages from this thread:https://www.eevblog.com/forum/testgear/power-supply-for-home-lab-do-i-really-need-a-rs/for the discussion leading to this more generic thread. It turns out quite a few lab power supplies (including those from A-brands), don't start in CC mode properly and have a huge current spike when the output is enabled. This huge spike can destroy sensitive components when wanting to use the supply as a current source instead of a voltage source.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 04:01:13 pm
content: ^ Exactly!!!47Ω, 50Ω doesn't really matter.DSO internal 50Ω should be fine as Current Limit is 40mA and DSO should be able to handle short period over current issue we are looking forBest,

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 04:18:51 pm
content: Is that correct?I asked a very similar question today about theDPS-150so I had the test setup more or less ready.I knew the Longwei PDS-3010G was really bad in this regard.Here is the proof.47Ω resistor.The DMM is there to display the 40mA (when it has settled), the LW can't display such small currents.Osc. Acq. mode is peak, therefore somewhat bold.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 04:22:30 pm
content: Quote from: nctnico on October 06, 2024, 03:18:48 pmA good example of this effect is when one is using an expensive IC and somehow gets the supply leads reversed, or the part plugged into the protoboard upside down, or the prototype wiring messed up, and so on: We've all been-there-done-thatAssuming one has set the Current Limit to a respectable value (always a good idea), this mishap hopefully would allow the expensive chip to survive. However, the high current overshoot on Power Supply Turn ON could destroy or severely damage the device, of course as Murphy would have it this will be the most expensive chip, not a LM358, or LM7805, but the ADC or DAC or ReferenceBest

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 04:25:10 pm
content: Quote from: Aldo22 on October 06, 2024, 04:18:51 pmIs the multimeter connected to the circuit some how?You do not want anything in between ... especially in series mode as a multimeter measuring A.It is altering the circuit.

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 04:29:45 pm
content: Quote from: Furna on October 06, 2024, 04:25:10 pmYes, there are 400mΩ extra so I can see what I'm doing.That doesn't make much difference in this case.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 04:35:01 pm
content: Quote from: Aldo22 on October 06, 2024, 04:18:51 pmNot sure how the interpret the scales on your DSO, but this doesn't look good!! Seems the supply takes ~ 6 divisions to return to the Current Limit 40mA set point. If that's 500ms/div then 3 seconds!! Even if the entire span is 500ms, then ~200ms which is quite long.Best,

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 04:39:27 pm
content: Quote from: mawyatt on October 06, 2024, 04:35:01 pmThe scope does not lie.It takes this long with 47Ω.It is faster with a “short circuit”.

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 04:49:19 pm
content: Quote from: Aldo22 on October 06, 2024, 04:29:45 pmYou do not know whatkindof resistor the multimeter has ... you are mixing type of resistors ... resistors have inductance.Could you please repeat the test without the DMM in series?

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 05:02:00 pm
content: Quote from: Furna on October 06, 2024, 04:49:19 pmYes, it's a bit different.But the overall impression of this PSU doesn't really change.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 05:02:25 pm
content: Quote from: Aldo22 on October 06, 2024, 04:39:27 pmWhat is the time scale, is it 500ms/Div?That looks like ~160mA for ~6 horizontal divisions!!!Best

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 05:05:56 pm
content: Quote from: mawyatt on October 06, 2024, 05:02:25 pmYes. (Top: Hantek -> Stop -> H ->500ms)Quote from: mawyatt on October 06, 2024, 05:02:25 pmYes. The DMM shows a Max of 174mA

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 05:07:43 pm
content: Quote from: Aldo22 on October 06, 2024, 05:02:00 pm... and the 100µs/Div?

author: mahi
author_rank: Regular Contributor
timestamp: October 06, 2024, 05:08:55 pm
content: Quote from: mawyatt on October 06, 2024, 01:40:11 pmShouldn't we take 1V/div because we already know certain power supplies will go up to 8V for a brief moment. Or don't we care about same scales for everyone?

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 05:13:50 pm
content: Quote from: Aldo22 on October 06, 2024, 05:05:56 pmSo ~160mA with 40mA Current Limit for 3 secondsBest

author: Aldo22
author_rank: Super Contributor
timestamp: October 06, 2024, 05:18:12 pm
content: Quote from: mawyatt on October 06, 2024, 05:13:50 pmYes. The DMM shows a Max of 174mA.It's all about the measurement. There was no question that this PSU is bad in this respect.That's why I asked today whether the DPS-150 is better.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 05:48:30 pm
content: Here's some measurements with 50Ω and Voltage set to 8V and Current Limit set to 40mA.#64 Siglent CH1 3303X @ 50ms/div#65 Siglent CH1 3303X @ 100us/div#66 Siglent CH2 3303X @ 50ms/div#67 Siglent CH2 3303X @ 100us/div#68 Instek CH1 GPP4323 @ 50ms/div#69 Instek CH2 GPP4323 @ 50ms/div#73 Korad KWR102 @ 50ms/div#74 Korad KWR103 @ 50ms/divBTW the Korad KWR102 is a SMPS with 30V/30A capability, and KWR103 is SMPS with 60V/15A capability.Best

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 06:07:00 pm
content: Here's the Turn OFF characteristics, all 50ms/div.#75 Siglent 3303X CH1#76 Instek GPP 4323 CH1#77 Korad 102#78 Korad 103Best

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 06:15:40 pm
content: 50Ω wire wound resistor; Voltage set to 8V and Current Limit set to 40mA.#31 Korad KA3005P @50ms/div PowerON#32 Korad KA3005P @50ms/div PoserOFFNo "overshoot" but voltage stay at 2.09V => 0.0418A (multimeter confirms) while PSU display shows 2.07V and 0.039A.Anyway for the price seems tollerable to me.@mawyatt could you add measurments to your caputure? Are the KWR102/KWR103 also "lying"?Why I insist on specifing wire wound? Because I am putting the PSU in the worst scenario.

author: mawyatt
author_rank: Super Contributor
timestamp: October 06, 2024, 06:39:27 pm
content: Quote from: Furna on October 06, 2024, 06:15:40 pmKWR102 reads 0.039A when set to 0.040A and KS34465A DMM reads 42.042mA, KWR 103 reads 0.039A when set to 0.040A and DMM reads 42.03mA.Best

author: mahi
author_rank: Regular Contributor
timestamp: October 06, 2024, 07:10:34 pm
content: Rohde & Schwarz HMP4040(pre-facelift): 4-channel power supply with 32V/10A (up to 160W per channel, 384W total) -datasheetMeasurements with voltage set to 8V, current to 40mA and a resistor of 50 ohm.Switch on:#1 HMP4040 CH1 switch on - 1V/div - 50ms/div (*)#2 HMP4040 CH1 switch on - 1V/div - 5ms/div (*) (**)(*) I had to take 1V/div instead of 500mV/div because of the overshoot(**) Due to the duration of the overshoot, it did not make sense to go shorter than 5ms/div, so no 100µs/div screenshot includedIn CC mode I'm measuring 39.75mA with a recently calibrated Fluke 289 (average because it actually fluctuates between 39.6 and 39.9mA) while the HMP4040 indicates 39.9 .. 40.1mA.Peak detect on the Fluke 289 measures 155.9mA at switch-on which is very close to what we can see in the oscilloscope measurements.(the multimeter was not in-circuit during the oscilloscope measurements)Switch off:#3 HMP4040 CH1 switch off - 500mV/div - 50ms/div#4 HMP4040 CH1 switch off - 500mV/div - 100µs/divI did not see differences in behavior between the channels, so I've included screenshots of channel 1 only.

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 08:19:11 pm
content: Quote from: mahi on October 06, 2024, 07:10:34 pmLooking at the datasheet I realized this PSU has also sense wires; did you try using sense?

author: mk_
author_rank: Regular Contributor
timestamp: October 06, 2024, 08:38:24 pm
content: Quote from: Furna on October 06, 2024, 08:19:11 pmfor CC-testing?

author: sonpul
author_rank: Regular Contributor
timestamp: October 06, 2024, 08:39:18 pm
content: RIDEN RD6006PSiglent SDS1202X-E 50ohm resistor.

author: Furna
author_rank: Frequent Contributor
timestamp: October 06, 2024, 08:53:33 pm
content: Quote from: mk_ on October 06, 2024, 08:38:24 pmIn the analog world it doesn't make any sense I know ... but in digital/software world it might.

author: Martin72
author_rank: Super Contributor
timestamp: October 06, 2024, 09:01:17 pm
content: Something else that occurs to me when I see all these pictures:At work, so-called discharge circuits are tested from time to time.The principle is simple: if the auxiliary voltage is removed (the device has been switched off), an FET conducts and the electrolytic capacitors in the DC link can discharge quickly via load resistors.And very quickly at that...So, now colleagues had the “problem” when testing this board that the discharge curve, which is normally very steep, drops rather “limp”.What's the problem? At the power supply unit that provides the auxiliary voltage for testing the board.We have dozens of laboratory power supplies with these “enable” buttons for the outputs.If you press this to turn it off, the voltage is not immediately gone, but decreases slowly - as some pictures here show.Do you know what I'm getting at...It is possible that some power supplies have a capacitance at the outputafterthe switch.That is why the output voltage is not immediately gone after switching off.

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2024, 11:07:20 pm
content: Quote from: Martin72 on October 06, 2024, 09:01:17 pm1) The on/off button isn't driving a relay but simply forces the output voltage setting to 0 at the point where the setpoint is fed into the output stage. I have modified quite a few power supplies to add this feature. Simply short the voltage control potmeter to ground to disable the output using a toggle switch. But in a digitally controlled PSU it is a simple matter of having the DAC which drives the output stage output 0V. Same principle though.2) The rapid discharge effect you are describing is a parallel power sinking circuit (Keysight calls this a downprogrammerhttps://docs.keysight.com/kkbopen/66xxa-down-programming-589741416.html) which kicks in when the output voltage is higher than then setpoint voltage. So when an output is switched off, this circuit will kick in because the output voltage is higher than the setpoint. But it will also kick in when power is fed into the power supply. Attach a fan and turn the output on / off. Chances are you see the current becoming negative due to the sink circuit absorbing the power from the fan while it is spinning down and working as a generator. However, this feature is not available in all power supplies so you need to check the specs. A way to tell whether a PSU has a sink circuit is when the voltage fall settling times are specified as well.

author: sonpul
author_rank: Regular Contributor
timestamp: October 06, 2024, 11:18:27 pm
content: The RD6006P has a 10uF output. When turned off, the output is shunted to ground by the circuit, accelerating the discharge of this capacitor. In my screenshot of the shutdown, you can see the beginning of the discharge first and then a sharp decline.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 07, 2024, 04:09:06 am
content: Please note that my resistor load is 45ΩR&S NGP804PS001: Turn ON without any slew control. Stays at 8V for approximately 16ms before exponential decay and settle into ~2V. Which means slightly more than 40mA setpoint. I don't have external DMM, but internal readback is 41mA.Scope reading hints even more than that (~44mA)PS002: Turn ON with 20ms slew setting. Peaked at 7.5V before decay. If you extrapolate out the initial jump, the slew is indeed approx 20ms, into 8V... (i.e. ~400V/s)PS003: Turn ON with 100ms slew setting. Peaked ar 4.7V before decay. Slew rate is approx 80V/sPS004: Turn ON with 200ms slew setting. More or less the same behavior. Peaked at 4.2V. Slew rate is indeed ~40V/s. SO far I still can't quite figure out what dictates the peak voltage w.r.t slew settings. It neither stays at constant voltage nor constant time.PS005: Turn OFF. No drama here. Interesting that the slope is linear instead of exponential.Keithley 2281SPS011: Turn ON with max (1000V/s) slew. Peaked all the way at 8V before decay. Slew rate is actually ~600V/s. Settling bang on at 1.80V, 400mA. Verified by DMM6500.PS012: Turn ON with 100V/s slew setting. Peaked at 3.7V. Slew rate is actually ~107V/s. Just like the R&S, peak points are neither at constant voltage nor time. Also note how it settles into 1.7V for a while before "snapping" into 1.8VPS013: Turn OFF with max (1000V/s) slew. Nothing weird other than the initial drop by ~100mV for 6.2ms before the distinctly stairstep slew down. Not sure how's the slew rate here, the stairstep section is ~1000V/s.PS014: Turn OFF with 100V/s slew. Similar behavior as before, only scaled up in time. Slew is indeed approx 100V/s in the linear section.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 07, 2024, 04:53:58 am
content: Like before, load is 45ΩGWInstek, Ithinkit is PPE-3323 although not really sure.PS021: Turn ON. (Almost) typical linear PSU behavior. Interesting that CV-CC switchover apparently happen at 200mV. It also sink ~0.5mA when output disabled, not unusual with certain design.PS022: Turn OFF. Your typical exponential output cap decay. Very slightly accelerated by 0.5mA sink.Interesting ripple, ~5.6s periodKeithley 2461PS031: Turn ON. Even a SMU have its quirks. Distinct three steps output: initial step into 50mV and stay there for a whooping 125ms, jumps into ~1.3V, before finally jumps into 1.8V. Output is bang on at 40mA.PS032: Zooming in at the weird bump. Not sure what it is.PS033: Turn OFF. Clean step, no drama here.

author: mahi
author_rank: Regular Contributor
timestamp: October 07, 2024, 04:57:54 am
content: Quote from: Furna on October 06, 2024, 08:19:11 pmThe 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.

author: 3isenhorn
author_rank: Contributor
timestamp: October 07, 2024, 08:01:33 am
content: I love the idea of collecting some data, so here is my share:1) Keysight E3640AThe control loop ramps up and then goes slowly to the limit. Since this supply has a low and high voltage mode (8V/20V), You see the results for turning on in low mode in Fig. 1 and for high mode in Fig. 2.2) Agilent E3614AAlthough similar in number, this has not a dedicated output button. When the supply is turned on, the output is on.When we turn on, as shown in Fig. 3, we see some ripple below 0.5V in the beginning, due to the mechanical turn-on switch.However, the control loop has a severe overshoot up to 6V for 116us, as shown in detail in Fig. 4.3) Korad KD3005PThe supply also has no dedicated outpouring on/off. Which led to a massive overshoot up to 8V and a small hick-up of around 0.2V in the beginning. As shown in Fig. 5.Figs. 6, 7, 8 and 9 show the corresponding tune-off behavior, with nothing too special.Hope this is helpful.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 07, 2024, 09:06:13 am
content: 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.

author: Furna
author_rank: Frequent Contributor
timestamp: October 07, 2024, 09:13:26 am
content: Quote from: mahi on October 07, 2024, 04:57:54 amThank you for your answer; next time I will also readbetterthe datasheet and the manualDifferent 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?

author: mhsprang
author_rank: Regular Contributor
timestamp: October 07, 2024, 11:15:10 am
content: Quote from: Furna on October 07, 2024, 09:13:26 amSense 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.

author: Furna
author_rank: Frequent Contributor
timestamp: October 07, 2024, 11:37:30 am
content: Quote from: mhsprang on October 07, 2024, 11:15:10 amAll correct but if you enable/disable sense, itmightalter 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.

author: mhsprang
author_rank: Regular Contributor
timestamp: October 07, 2024, 11:56:01 am
content: Quote from: Furna on October 07, 2024, 11:37:30 amFirst of all, as auserof 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.

author: Furna
author_rank: Frequent Contributor
timestamp: October 07, 2024, 12:12:17 pm
content: Quote from: mhsprang on October 07, 2024, 11:56:01 amWe 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

author: pdenisowski
author_rank: Super Contributor
timestamp: October 07, 2024, 02:29:19 pm
content: Quote from: mhsprang on October 07, 2024, 09:06:13 amWe 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.

author: mawyatt
author_rank: Super Contributor
timestamp: October 07, 2024, 02:57:02 pm
content: 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

author: Furna
author_rank: Frequent Contributor
timestamp: October 07, 2024, 04:57:00 pm
content: Quote from: mawyatt on October 07, 2024, 02:57:02 pmFor whom is not following the Siglent SPD4000 series thread, my measurements of Siglent SPD4121X are available athttps://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667709/#msg5667709https://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5667823/#msg5667823Siglent SPD4000 series has 4 channels that are inerhently different ...SPD4121X in particular hasCH1-CH4 15V 1.5A are independentCH2-CH3 12V 10A can be setup in series/parallel and both also have 4wire sense

author: Antonio90
author_rank: Frequent Contributor
timestamp: October 07, 2024, 06:13:18 pm
content: A few measurements from the GPD-4303S and the Yokogawa 7651 DC source.Please note, all measurements done with standard 10X probes, and 8v 40mA,exceptchannel 4 from the GPD, which only goes to 5.2V.Resistor measured at around 54.17 Ohms.Edit: The math trace is the current at 20mA/div (i think it is pink?)

author: _Wim_
author_rank: Super Contributor
timestamp: October 07, 2024, 07:11:03 pm
content: A few of the power supplies I own (for the fast ones, I also added a 2ms timebase). Test with 50ohm resistor / 8V / 40mA. Interesting is the GS200, which can work in current mode and voltage mode.

author: Martin72
author_rank: Super Contributor
timestamp: October 07, 2024, 09:10:58 pm
content: Quote from: nctnico on October 06, 2024, 11:07:20 pmRegarding 2):I may have expressed myself a little misleadingly (or the translator).I actually wanted to explain how most of the off-state images here come about, using a practical test example on an assembly.Be that as it may, I may get around to adding a few pictures of this this week, but of Peaktech power supplies...

author: mawyatt
author_rank: Super Contributor
timestamp: October 07, 2024, 09:23:37 pm
content: Quote from: Furna on October 07, 2024, 04:57:00 pmThat's unusual that CH1 and CH4 are the same and CH2 and CH3 are the same but different from CH1 and CH4, this explains the difference since CH1 (15V 1.5A) is not the same specification as CH2 (12V 10A) and thus one might expect a different response from such!!Now looking at the Siglent page for the SPD4121X shown, this arrangement looks OK with terminals for CH1 logically on left then the channels proceed to right as 2 thru 4 (not like GPP 4323 where Instek placed CH4 on left, then2 thru 41 thru 3 towards rightThe 4000 display shows 1 to 2 top and 3 to 4 below left to right which makes sense, however because of the arrangement the similar channels are diagonal not left to right as one would expect!!Imagine using a typical analog supply arrangement of +-15V (or +-12V), then the important display channel parameters (V and I) are diagonal not left to right for the active channels. So glancing at the active channels in this common use case requires determining the individual channel parameters on diagonals rather than side by side!!This makes no sense IMO, would like to hear the logic behind this arrangement from Siglent designers!!!https://siglentna.com/power-supplies/spd4000x-series-programmable-linear-dc-power-supply/Best,

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2024, 10:03:06 pm
content: Quote from: mawyatt on October 07, 2024, 09:23:37 pmAll three SDP4000X models have quite different ratings.Ch 1&4 are equal and likewise Ch 2&3 but different for each model.Check out P4https://int.siglent.com/u_file/download/24_08_14/SPD4000X_DataSheet_EN01B.pdf

author: mawyatt
author_rank: Super Contributor
timestamp: October 07, 2024, 10:19:13 pm
content: Quote from: tautech on October 07, 2024, 10:03:06 pmSee edited notes after your post.If a supply has equal dual pairs of channels they should always be arranged in a 1,2 and 3,4 fashion, not in 1,4 and 2,3 arrangement IMO. These should be displayed in a 1,2 on top and 3,4 on bottom so one can easily compare like channels.Best,

author: thm_w
author_rank: Super Contributor
timestamp: October 07, 2024, 10:21:22 pm
content: Rigol DP832was shown above, as I mentioned in the other thread, it does have some small overshoot to 15-20mA so its relevant if you are current limited sub 10mA, which is very low.Rigol DP932Channel 1 - no overshoot:R&S NGMOhigh speed power supply - Overshoots to 8V:

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2024, 11:56:15 pm
content: Quote from: mawyatt on October 07, 2024, 10:19:13 pmAdded.While I don't speak for them, what they have done does make some sense to me.You've used a split rail+argument to support your POV yet in Ch 2-3 Series mode one can pull 0V from the center connection for dual tracking supply needs without any need for external cabling and only 2&3 support Series and Parallel modes and Sense.As Ch 1&4 don't provide Series or Parallel modes or Sense it's not logical they need be grouped together even for split rail use as they can't be Series'd for dual tracking supply use.This does however bring additional thoughts forward, should Ch 1&4 have instead been paired and given Series and Parallel capability some major changes to the design and UI would be needed, otherwise how would one know which channels were being Paralleled or Series'd ?@FurnaWhat is the display indication when Ch 2&3 are used in Series and Parallel modes ?

author: mawyatt
author_rank: Super Contributor
timestamp: October 08, 2024, 12:50:53 am
content: QuoteThe SPD3303X and GPP4323 both allow creating a Dual Voltage Tracking Supply utilizing the Series Mode on CH1 and CH2 without any "extra" cabling also, altho the SPD3303X doesn't read the current thru/from CH2 properly (serious flaw IMO). Example drawing a different current from CH2 while in the Series Mode doesn't show in the CH2 current display. Apparently this is just displayed as a replica of the CH1 currentThe GPP4323 reads this condition properly and displays the correct current drawn from both CH1 and CH2 while in Series Mode, whether thru or from both channels or some current "tapped" off from CH1 or CH2.This dialog has allowed us to discover a potential issue with the SPD3303X that we didn't know, as we don't recall ever seeing this discussed before. Maybe others can do this test in addition to the ON/OFF characteristics?If you or Furna have the time please check the SPD4000X in Series Mode and see if CH2 and CH3 display the correct current drawn respectively. Just place a resistor across either CH2 or CH3 and see if it registers properly on the respective channel display, then attach across the full series span of CH2 and CH3, this should show twice the current and displayed in both channels as flowing thru both.Anyway, good discussionsBest

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2024, 12:58:04 am
content: Sorry Mike, no SPD4kX here yet.A few weeks....

author: mawyatt
author_rank: Super Contributor
timestamp: October 08, 2024, 01:01:46 am
content: Maybe Furna can helpBTW do you recall this issue with the SPD3303X mentioned?Best

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2024, 01:14:44 am
content: Quote from: mawyatt on October 08, 2024, 01:01:46 amSplit rail current measurement, no.....maybe it's the advancing years.

author: BennoG
author_rank: Frequent Contributor
timestamp: October 08, 2024, 10:37:49 am
content: Ok I tested all my power supply's to see if this is a common problem.Agilent 6645A OkEA PS 2084-10B OkKeithley 2231A-30-3 CH1 (overshoot)Keithley 2231A-30-3 CH2 (overshoot)Keithley 2231A-30-3 CH3 OkKeithley 2400 OkAgilent N6700B CH1-CH4 OkRiden DPS5005 OkRiden RD6012 OkRiden RK6006 OkSpellman SL2000 (overshoot) not fair because this is a 1kV 2A 2kW psuTDK Genh60-12.5 OkBenno

author: mhsprang
author_rank: Regular Contributor
timestamp: October 08, 2024, 11:28:12 am
content: I found an article about overshoots in power supplies, dependant on the priorities of the voltage control loop and current control loop:https://www.electronicdesign.com/technologies/power/article/21801598/getting-your-priorities-straight-managing-overshootsWhile I have never written a control loop for a power supply, as an embedded programmer I keep wondering why you can't combine those loops or at least observe crossing the V and I limits at the same time and act accordingly?

author: Geofrey
author_rank: Contributor
timestamp: October 08, 2024, 02:58:15 pm
content: Hi, I attached the results for my BCS6401. CH1 is on a 4wire configuration, CH2 is not. It did not cross test to see what factor is causing the overshoot as I would need some time to change the back wiring.Overall I would say fast response, but with some overshoot, unless I do not set the "fast speed" setting but "normal speed" instead. Interestingly, a set rise time comparable to the "normal speed" do result in overshoot.Also attached the results of my belovedMulticomp MP710087 (Owon P4305 rebadge) that never fails to impress me. The settling isn't at 40mA but at 101mA as I cannot calibrate the current offset to less than roughly 80mA. So I calibrated it to 100mA offset just to get somewhat legible reading on its screen.

author: _Wim_
author_rank: Super Contributor
timestamp: October 08, 2024, 04:56:37 pm
content: Quote from: mhsprang on October 08, 2024, 11:28:12 amYou can. In industry we call this an "overide" control (also called sometimes select control). This is used when you have multiple PVs (process values) and only a single CV (control value). In our case we have measured voltage AND measured current as "PVs", and typically output voltage as "CV" (but this could be output current also as on the Yokogawa GS200 above). This article briefly describes override control (https://www.pid-tuner.com/wp-content/uploads/2019/07/Override_for_all.pdf), but once you know how it is called, there is tons of information available on the net.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 08, 2024, 07:19:30 pm
content: HP 66311B on and off:Siglent 3303X (hacked from RS Pro 3303X-E) on and off:Will try HP 6633B and TTi EX354 later

author: Furna
author_rank: Frequent Contributor
timestamp: October 08, 2024, 08:13:53 pm
content: Quote from: tautech on October 07, 2024, 11:56:15 pmSee images

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2024, 08:22:56 pm
content: Quote from: Furna on October 08, 2024, 08:13:53 pmThanks.Nice, I didn't notice the bicolor LED lit Series/Parallel button in the short play I had with one at HQ.

author: Furna
author_rank: Frequent Contributor
timestamp: October 08, 2024, 08:26:36 pm
content: Quote from: mawyatt on October 08, 2024, 12:50:53 amI do not have much time now; buthttps://www.eevblog.com/forum/testgear/new-siglent-spd4000x-series-power-supply/msg5630671/#msg5630671Maybe tomorrow I can go through this better.

author: Furna
author_rank: Frequent Contributor
timestamp: October 08, 2024, 10:04:06 pm
content: CH2 in series with CH3CH2 is "master"; you cannot setup CH3CH2 set to 5V and 5Ω01_IMG_20241008_230601.png10Ω across CH2 (red and black cables)CH2 shows total volatge 5V (CH2+CH3) 0.247A demonstrates CH2 outputs 2.5VCH3 outputs 2.5V but note green cable disconnected => 0A02_IMG_20241008_225937.png10Ω across CH2 (red and black cables)50Ω (2x100Ω in parallel) (blue and green cables)CH2 shows total voltage 5V (CH2+CH3) Amper is again the sum (CH2+CH3) 0.346ACH3 shows 2.5V and 0.1A of CH303_IMG_20241008_235241.png20Ω across CH2 (red&black)50Ω across CH3 (yello&green)10Ω across the series (red&green)

author: mawyatt
author_rank: Super Contributor
timestamp: October 09, 2024, 01:43:11 am
content: @ FurnaThanks for the post, could you repost the above over here:https://www.eevblog.com/forum/testgear/power-supply-series-mode-for-split-dual-tracking-use/We have response prepared but realized it's better in the above thread for folks to follow, and didn't want to copy your post without permission, and didn't want to clutter this thread up since it's dealing with ON/OFF characteristics.Best

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 09, 2024, 02:12:00 am
content: Quote from: mawyatt on October 09, 2024, 01:43:11 amYou can quote him from this thread in the other thread with a little copy-paste magic.

author: colorburst
author_rank: Regular Contributor
timestamp: October 09, 2024, 05:19:16 pm
content: Harrison 865CMastech HY3005D-3Electro Industries DIGI-35A

author: AVGresponding
author_rank: Super Contributor
timestamp: October 09, 2024, 07:09:27 pm
content: Quote from: AVGresponding on October 08, 2024, 07:19:30 pmRevisited this, as I realised I'd used a4R7resistor instead of a47R...3303X:66311B:Apologies for any confusion my blind-assed dumbshittery may have caused

author: Furna
author_rank: Frequent Contributor
timestamp: October 09, 2024, 08:03:42 pm
content: Quote from: mawyatt on October 09, 2024, 01:43:11 amAnswered there

author: mawyatt
author_rank: Super Contributor
timestamp: October 09, 2024, 08:20:35 pm
content: Quote from: AVGresponding on October 09, 2024, 07:09:27 pmNo worries, we've all been there done that especially with color coded components, heck we've even done this with numeric coded componentsYour 3303X looks like ours wrt the ON waveform. Seems the short duration "glitch" at initial ON condition is independent of the PS settings, either Current limit or Voltage setting.Anyway, thanks for updateBest,

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 09, 2024, 08:45:32 pm
content: Quote from: mawyatt on October 09, 2024, 08:20:35 pmI had a thought about this that's slightly weird I guess. But the current setting is a setting, not really a limit. So I tried adjusting OCP (hold down the right arrow under the knob on the 3303X), and that had absolutely no effect on the ~29mA turn on spike when using 10mA as the setting & OCP limit. I haven't tried higher levels yet.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 10, 2024, 07:59:08 am
content: Quote from: mawyatt on October 09, 2024, 08:20:35 pmOh, it's worse than that; these were 10W epoxy coated wirewound, marked 4R7...bd139 suggested it might be the inductance (not knowing of my mistake), so I paralleled six 270Ω carbon composition resistors together, and got the results you see in my updated post. It was some minutes of head scratching until I realised what I'd done.EDIT: Some recent experiments with some NOS 1N827's has shown me that using these psu's as a precision current source just doesn't work; the output is too unstable. The only way to get a stable output current is in CV mode by using a limiting resistor and getting the current you want by means of setting the voltage appropriately and avoiding going anywhere near CC mode.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 10, 2024, 08:31:45 pm
content: Here's the on and off characteristics of my v6.2 hw 3303X. As I mentioned in the other thread, there's no spike above the V&A settings when set above 30mA.This is CH1. There's always a fast spike to ~29mA when the channel is activated.Thanks,Josh

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 10, 2024, 08:47:44 pm
content: Similar performance with CH2.Going back to my previous comment aboutSettingsvs.Limits(since this is not actually limits that we're adjusting). I can set OCP to 30mA or whatever below the 40mA channel setting, and it will shut off the PSU output promptly after I activate it.Thanks,Josh

author: Martin72
author_rank: Super Contributor
timestamp: October 11, 2024, 02:08:47 pm
content: Peaktech 62278V, 40mA, 47 Ohm Resistor.LeCroy WS3024Z, Siglent CP6030.Very controlled power-on process. When switching off, you can clearly see that an electrolytic capacitor discharges at the output of the power supply.Remedy: mechanical switch between power supply and DUT.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: October 12, 2024, 12:08:52 am
content: Here are some plots from an Agilent U8001A. Load is 47 ohm non-inductive. MXO4 with RT-ZP11 probes. I set the voltage to 15V, with various current limits. At 500 mA, the supply was in CV mode, all others were CC. I toggled the on/off switch rapidly to see both rise and fall slopes. I noticed a glitch would sometimes show up, I captured one on the 500 mA setting, though it did happen at others too.It seems quite well behaved, but I think this PS had killed a board I was testing due to transients during CC/CV switching.edit: sorry, filenames say '10V' but the supply was set for 15V.

author: thm_w
author_rank: Super Contributor
timestamp: October 12, 2024, 12:29:54 am
content: Quote from: radar_macgyver on October 12, 2024, 12:08:52 amBut did you test the settings as specified in the OP... 8V and 40mA?

author: mhsprang
author_rank: Regular Contributor
timestamp: October 12, 2024, 09:48:04 am
content: Quote from: thm_w on October 12, 2024, 12:29:54 amThas it indeed important as on the R&S NGE 103 the problem disappears above 150 mA. This behaviour is all about low currents. My tests were all done at 10 mA, when testing (and frying) some LEDs.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: October 12, 2024, 06:43:08 pm
content: Quote from: thm_w on October 12, 2024, 12:29:54 amAh crap, will re-do with those settings, that was at work so it'll be a couple of days. In the meantime, here's the results from my home bench, with a TTi MX100TP and a Siglent SDS2104X Plus. The 40mA test shows an overshoot, and interestingly, the overshoot behavior at higher current limits starts to show a pattern, its like the control loop stays in CV mode till the voltage reaches 2.5V before it switches to CC mode. I tried various ranges supported and they all showed the same behavior (this supply lets you internally combine its three outputs to create several ranges). No difference between the output channels either.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 13, 2024, 09:05:24 am
content: HP 6633B here. Quite a bit slower to regulate than others:

author: AndyC_772
author_rank: Super Contributor
timestamp: October 13, 2024, 10:19:23 am
content: I carried out quite a detailed investigation of this effect on the 6632B some years ago...https://www.eevblog.com/forum/beginners/first-bench-supply-ripplenoise-problems/msg141522/#msg141522

author: tautech
author_rank: Super Contributor
timestamp: October 13, 2024, 10:21:33 am
content: Siglent SPS5042X < 40V 60A capable.Set to 8V 40mA > 56 Ohm 10W < first to hand.....Screenshots in this order:Small step and some ripple at ON.Clean ramp down at off.Close in analysis of the power ON step.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 14, 2024, 05:21:51 am
content: This appears to show the SPS5042Xnotgoing in to CC..?

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2024, 05:36:17 am
content: Quote from: AVGresponding on October 14, 2024, 05:21:51 amStudy the V/div settings.

author: Kean
author_rank: Unknown
timestamp: October 14, 2024, 05:45:56 am
content: Quote from: tautech on October 14, 2024, 05:36:17 amThe first trace shows it exceeding 2.24V (40mA over 56ohms) for at least 40ms, and hitting the 8V CV setting.The second trace (ramp down at power off) shows it was eventually in CC mode, but you don't show a longer timescale from power on to see it going from CV to CC mode.It also looks like it was in CC at about 2.4V so probably closer to 45mA than 40mA.

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2024, 05:57:35 am
content: Quote from: Kean on October 14, 2024, 05:45:56 amOSD = 44mA

author: mawyatt
author_rank: Super Contributor
timestamp: October 14, 2024, 04:00:27 pm
content: Rob,We agree with Kean.This looks as if the CC is attempting in the 1st graph at ~5V, but voltage across 56Ω resistor continues up to 8V which is Voltage setting. If true CC Mode were active, then the voltage across the 56Ω resistor would limit at 40ma*56Ω = 2.24V and not continue to 8V.Edit: Added response with 56Ω Resistor with SPD3303X, showing voltage across resistor. Note how the response approached the CC Setting of 40mA as set (2.24V across R) with the CV is set to 8V.Can you rerun this 1st plot with time scale at 50ms/div (or longer if necessary) to show the supply output returning to the proper CC set to 40mA*56Ω or 2.24V?Best,

author: David Hess
author_rank: Super Contributor
timestamp: October 14, 2024, 06:11:16 pm
content: Here are the waveforms for a Tektronix PS503A power supply set for 8 volts and 80 milliamps. This power supply has 50 microfarads of output capacitance. The output control switch operates by controlling the reference. Neither the voltage or current control loops are clamped.The current waveform had some variation so I recorded multiple examples with my DSO set to accumulate them. The peak excursion with current limiting was 1 volt higher than the nominal 4 volt output into 50 ohms. I have no idea why this variation exists.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: October 14, 2024, 06:32:45 pm
content: Startup for the Agilent U8001A again, this time with 8V and 40mA settings. The only 'odd' thing I see is the fast rise to ~250 mV before the much slower rise to the final 2V. The behavior is similar on other current limit settings and in constant voltage mode.

author: Aldo22
author_rank: Super Contributor
timestamp: October 17, 2024, 01:11:34 pm
content: Fnirsi DPS-150Nice behavior when switching on and off with the button, but full 8V at the beginning if you just plug in the cable.

author: BennoG
author_rank: Frequent Contributor
timestamp: October 17, 2024, 02:08:15 pm
content: Quote from: Aldo22 on October 17, 2024, 01:11:34 pmThe hard cable connection is expected because the PSU has some capacitors that needs to be discharged before current limiting can start.Benno

author: Aldo22
author_rank: Super Contributor
timestamp: October 17, 2024, 02:30:31 pm
content: Quote from: BennoG on October 17, 2024, 02:08:15 pmThank you.I don't know how other "better" PSUs behave.Anyway, you should keep in mind that you are probably not absolutely safe from overcurrent if the connection is interrupted for a short time.

author: hp3310a
author_rank: Regular Contributor
timestamp: February 21, 2025, 01:54:49 pm
content: Korad KD3305DSet to 8V, 40mA limit47Ohm

author: David Hess
author_rank: Super Contributor
timestamp: February 21, 2025, 04:48:54 pm
content: Quote from: David Hess on October 14, 2024, 06:11:16 pmI replaced the 741 error amplifiers with much faster TL071s and got the following results. The voltage ramp was identical. The occasional overshoot in the current ramp was completely removed, however spikes near the corner of the current ramp became evident which I suspect are very brief periods of oscillation. This might be cured with a little bit of frequency compensation, or maybe improved supply decoupling at the operational amplifiers. When LF351s were used, the overshoot was also completely removed, however the brief periods of oscillation were up to 10 milliseconds long and located both at the knee and before the trigger.The photo shows an accumulation of very brief oscillations over multiple tests with the TL071. Original photo using 741s also included.Update: messed around with it and adding power supply decoupling completely solves the oscillation problem. The current ramp then becomes perfect.

author: Bernd_2
author_rank: Contributor
timestamp: August 17, 2025, 07:56:18 pm
content: Hello,Here are the measurements taken with a Uni-T UDP6932B power supply. 60 volts, 10 A max, and 200 W maximum power.Setting: 8 V, 40 mA on a 50 ohm rotary resistor. Current measurement with Micsig CP1003B.As you can see, the current and voltage rise so slowly when switching on that there are no overshoots. There are also no oscillations or glitches when switching on and off.Best RegardsBernd

author: Martin72
author_rank: Super Contributor
timestamp: August 17, 2025, 09:41:57 pm
content: Hi,If I interpret the instructions for the power supply correctly, you can change the rise time.I would check that first, otherwise you would have to “hard switch” externally to be able to observe the power supply control.

author: Helix70
author_rank: Unknown
timestamp: August 17, 2025, 09:45:04 pm
content: Here are my results:8V 50 Ohm 40mAHP 3634A 25V RangeHP 3634A 50V RangeEvox EEZ H24005(Hmm, lots of ripple!)Regards,Josh

author: Martin72
author_rank: Super Contributor
timestamp: August 17, 2025, 10:15:17 pm
content: Hi,QuoteWhat signal do we see on your images when the channel is set to 500 mV/div?

author: BillyO
author_rank: Super Contributor
timestamp: August 18, 2025, 06:29:50 pm
content: Someone asked about that little PS from everyone's most hated company?Well, here it is. The FNIRSI DPS-150. Sorry to disappoint everyone but, it's not truly awful .. although better that supplies shown here that cost 10 times as much (or more?), I'm sure some will find something about it that just makes it the worst power supply in the planet.

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 18, 2025, 06:47:32 pm
content: Quote from: BillyO on August 18, 2025, 06:29:50 pmCan you run the test in the lower range? Like a 10mV or 30mV test? And please turn on the grid labels for your screenshot.

author: BillyO
author_rank: Super Contributor
timestamp: August 18, 2025, 06:53:04 pm
content: Quote from: KungFuJosh on August 18, 2025, 06:47:32 pmI'm not sure what you are asking for Josh.Do you want me to use 10mV instead of 8V?I put cursors on the over shoot. Peak of 0.39V trailing away in 55ms

author: Bernd_2
author_rank: Contributor
timestamp: August 18, 2025, 06:55:49 pm
content: Hello Martin,Thank you for pointing out the adjustability of the slew rate on the UDP6932B. The device has three settings: Normal, CV-Slew Rate, max. 124 V/s, and CC-Slew Rate, max. 21 A/s.The measurements inPost #97were taken with the CC-Slew Rate setting at21 A/s.Today, I repeated the measurements with the Normal and CV-SlewRate 124 V/s settings.While the result for Normal is the same as for CC-SlewRate 21 A/s, there is a significant overshoot with the CV-SlewRate 124 V/s setting.Voltage and current rise to approx. 4 Volts and approx. 84 mA within approx. 50 ms and then fall to the set limit value within approx. 450 ms.Best RegardsBernd

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 18, 2025, 07:19:29 pm
content: Quote from: BillyO on August 18, 2025, 06:53:04 pmI'm curious how it looks in the lower range. See my attached SPD3303X as an example.

author: BillyO
author_rank: Super Contributor
timestamp: August 18, 2025, 07:26:41 pm
content: I'm still not getting it. Maybe I banged my headYour vertical volts is at 400mV/div, mine was at 500mV/div. Not much difference there.Also, the scope I'm using is the one in my office. It's only a SDS1204X-E, so I can't label the grid.Edit: What's with those trace labels?

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 18, 2025, 08:04:38 pm
content: I think they're self-explanatory.

author: Helix70
author_rank: Unknown
timestamp: August 19, 2025, 01:00:42 am
content: Quote from: Martin72 on August 17, 2025, 10:15:17 pmWhat do you mean? The Oscilloscope channel is 500mV/division already.The 8V is the voltage set point on the power supply, 40mA is the current limit setting, and 50 Ohms is the load resistor.Then I enable the output and you see the voltage output for the off->on transition, and then the voltage fall for the on->off transition.

author: Martin72
author_rank: Super Contributor
timestamp: August 19, 2025, 09:22:33 pm
content: In each of your pictures, a maximum of 2V can be seen on channel 1. Is that the output voltage of your power supply?Or is that the voltage across a (fairly high-impedance) shunt?

author: BillyO
author_rank: Super Contributor
timestamp: August 19, 2025, 09:42:54 pm
content: Quote from: Martin72 on August 19, 2025, 09:22:33 pmWho are you asking?

author: Martin72
author_rank: Super Contributor
timestamp: August 19, 2025, 09:47:51 pm
content: If I don't quote anyone, I usually respond directly to the previous post.

author: BillyO
author_rank: Super Contributor
timestamp: August 19, 2025, 09:57:23 pm
content: Oh, okay, understood.Don't mean to answer for him, but I assume he is using the set-up described in the first post. Set the supply to 8V & 40ma current limit. Attach a 50ohm resistor, then put your scope across the resistor. Turn on (and off) the power supply and record the voltage over time.I guess the idea is, if the supply is slow in getting the current limit engaged you will get a spike .. up to 8V, then it should settle out to 2V (40ma through 50ohm).If it does get the current limit in place properly, you will see the voltage rise to 2V and stay there.And everything in between. Like the little .39V overshoot of teh FNIRSI.

author: Helix70
author_rank: Unknown
timestamp: August 19, 2025, 10:50:03 pm
content: Yes, BillyO is correct. The images show the voltage across the 50 ohm shunt, which is being limited to 2V due to the 40mA current limit set on the power supply and 50 Ohm load. No overshoot - good!Regards,Josh

author: BennoG
author_rank: Frequent Contributor
timestamp: August 20, 2025, 07:29:09 am
content: TTi MX100QP should be a reputable brand.But the overshoot is enormous. It goes to 8V for about 15-20 ms and then drops down.Also dit a test on lower resistors (0.5 and 0.2 ohm) and on turn on it could go up to 15A for 1 or 2 ms (current limit still 40mA 8V)This is positive if you are testing devices that have a huge capacitor at the input.But is negative if you are testing a MCU that has a short somewhere.Even when testing a LED you can blow up the LED with this.edit added the turn offBenno

author: jusaca
author_rank: Unknown
timestamp: August 20, 2025, 11:26:34 am
content: I think there was no status report for the R&S case since last october in this thread. Was there any real feedback from them regarding the overshoot?

author: Bernd_2
author_rank: Contributor
timestamp: August 20, 2025, 05:58:18 pm
content: Hello,Here is an addition to the measurements on the UDP6932B, posts #97 and #104. To see if the overshoot behavior changes at higher currents, I took three measurements with a current limit of 1 A. All with CV slew rate 124 V/S.Figures 1 and 2 show the measurement with 8 V voltage and 1 A current limit at 5 ohms. As you can see, the current only overshoots by about 30% and then settles at 1 A after 120 ms.Figures 3 and 4 show the curve with a voltage limit of 60 V and a current limit of 1 A at 5 ohms. Now the current shoots up by 37% and falls to the set value of 1 A after 110 ms.Figures 5 and 6 show the measurement with a voltage limit of 60 V and a current limit of 1 A at 50 ohms. Now the current no longer shoots up and only reaches the set value of 1 A after approx. 550 ms.Best RegardsBernd

author: Mahagam
author_rank: Regular Contributor
timestamp: August 20, 2025, 06:42:58 pm
content: Siglent SPD1168X. Not bad.No OFF plot, because it looks like standard discharge RC = 49.48Ω * 500μF

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2025, 06:45:36 pm
content: Quote from: jusaca on August 20, 2025, 11:26:34 amDo you mean the R&S NGMO?I wonder if there is something in common for all of these supplies with such poor overshoot. Do they use a digital feedback loop? Properly implemented a digital feedback loop should be no worse, and likely better than an analog one.It would be useful to know how much output capacitance they have.

author: Thomas
author_rank: Regular Contributor
timestamp: August 20, 2025, 06:52:52 pm
content: TTi EL302RT and GWInstek GPP-4323.I didn't record channel 2 on the GPP-4323 since it is identical to channel 1.

author: d-el
author_rank: Regular Contributor
timestamp: August 20, 2025, 08:57:17 pm
content: DIY power supplies are valid?Quick specs: 1 channel, 37V, 4A, LAN interface, weight less than 4kg.Precondition:DSO: LeCroy WR104MXi, BWL 20MHz, Coupling DC50Ω, 500mV/DivPS: 8V, 40mAON:OFF:PS:

author: BillyO
author_rank: Super Contributor
timestamp: August 20, 2025, 09:25:42 pm
content: This is a cheapie I got for the 20A capability which I rarely need, but it's turned out to be a pretty nice supply.Bside I84020 300W SMPS. Got it for $100 on AliExpress. Could not get exactly 40mA as the adjustment resolution is 10mA. Looks like it might be a little high. Over shoot is about .1V

author: Martin72
author_rank: Super Contributor
timestamp: August 20, 2025, 09:35:04 pm
content: If this thread is intended to show the settling time of the respective power supplies during loading and unloading, then your last image does not show any regulation, as it is simply a capacitor that is apparently located directly at the output after the (electrical) output switch that is discharging.

author: BillyO
author_rank: Super Contributor
timestamp: August 20, 2025, 09:42:12 pm
content: No argument here. At least it does not spike.

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2025, 10:05:24 pm
content: In a lot of these cases it seems they added enough output capacitance to make up for poor transient response from poor frequency compensation.Usually only about 50 microfarads per amp is required, but variation from half to twice that is common. With care and good design, a good low capacitance design is possible with a fraction of a microfarad per amp.

author: BillyO
author_rank: Super Contributor
timestamp: August 20, 2025, 10:09:49 pm
content: Well, sure. Again, no argument. But can you expect that level of design and execution in a power supply that costs under a couple of hundred bucks?

author: BennoG
author_rank: Frequent Contributor
timestamp: August 21, 2025, 05:39:08 am
content: the TTI MX100QP I have is about 1800euro ($2000) and has a overshoot to the full 8V and after 15 ms it dials back.The $40 Riden RK6006 works as perfectly as you can wish.Benno

author: Mahagam
author_rank: Regular Contributor
timestamp: August 21, 2025, 08:58:52 am
content: Quote from: David Hess on August 20, 2025, 10:05:24 pmSiglent SPD1168X. Settings are 16V & 10mA. Initially shorted by ampermeter (shows me 10.256mA). Estimated capacitance is 930μF

author: BennoG
author_rank: Frequent Contributor
timestamp: August 21, 2025, 09:39:48 am
content: Again the TTI MX100QP with various capacitance at the output still 8V 40mA into 50 ohmYellow = no capGreen = 330uFRed = 470uFpurple = 1000uFblue = 2200uFNote rise time is still less than 2 ms very impressive of the MX100QPI guess the fast rise time makes it hard to implement the current limit within this time.My guess is in the first 2 ms the PSU dumps a couple of A into the capacitor.Edit added measurement of the current dumped in the 2200 uF capacitor (11.5A) for 0.3msSee scope traces overview and zoom.

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2025, 01:57:04 pm
content: Quote from: BennoG on August 21, 2025, 09:39:48 amRise time should be limited by the 40 milliamp current limit into the output capacitance.Somehow it looks like the output current is unlimited immediately after the output is turned on, which could be just the current limit being slow to activate for whatever reason. 2 milliseconds is not that fast.

author: BennoG
author_rank: Frequent Contributor
timestamp: August 21, 2025, 02:46:32 pm
content: Quote from: David Hess on August 21, 2025, 01:57:04 pmYes the high current on turn on is the only problem of this unit, i have contacted TTi about this but got no response from them.During testing I found it dumps 20A in a short circuit for about 0.2 ms or so. This is not what you want for testing of a microprocessor board that you are testing.

author: mawyatt
author_rank: Super Contributor
timestamp: August 21, 2025, 03:42:22 pm
content: It's quite surprising this many modern Lab Type PSs from quality OEMs have this kind of issue. Maybe some OEMs will pick up on this and rethink newer designs before release.Best

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 21, 2025, 04:17:50 pm
content: 30 years passed, so many tech advances and I agree with you that still we are in same point where one can damage his project accidentally even on some PSUs having output ON/OFF switch I seen :/

author: mawyatt
author_rank: Super Contributor
timestamp: August 21, 2025, 05:12:54 pm
content: We lost a pair of $50K custom chip sets due to a Turn OFF/ON glitch decades ago, so are overlysensitiveto this effect!!Best

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2025, 06:39:34 pm
content: Quote from: mawyatt on August 21, 2025, 03:42:22 pmThe engineering has been a solved problem for decades. I would like to know how they made this mistake, but it appears to be a common one.The examples I posted from a Tektronix PS503A showed a tiny amount of overshoot in current mode, which I corrected, (1) but further inspection of the schematic shows that Tektronix included a specific startup circuit which clamps the reference until the control circuits are fully powered, preventing output glitches. The Tektronix designers was obviously paying attention to startup performance.(1) The variation of the overshoot makes me suspect that some 741 operational amplifiers worked and some were marginal in this application. Changing the operational amplifier used for current control to one with a faster slew rate completely solved it. Adding anti-windup, which would also prevent saturation, might solve it also.

author: Martin72
author_rank: Super Contributor
timestamp: August 21, 2025, 07:45:41 pm
content: Quote from: mawyatt on August 21, 2025, 05:12:54 pmThat was one of my nightmares two decades ago...I created a test setup for a European-format circuit board equipped with 23 CMOS logic chips.The supply voltage was 15V, and I used one of the new, inexpensive power supplies.I tested half of the board, took a break, and turned off the power supply.When I turned it back on after the break, the power supply went into current limiting mode and the board became boiling hot – what had happened?These were adjustable power supplies ranging from 0 to 50V. When switched off, the regulator no longer worked and the power supplies briefly supplied the full 50V... All ICs on the board were dead.The next day, all power supplies of this type were thrown away.

author: Martin72
author_rank: Super Contributor
timestamp: August 21, 2025, 08:07:26 pm
content: Quote from: BennoG on August 21, 2025, 02:46:32 pmThen the output capacitor will be located directly at the output—no chance for the current regulator to intervene quickly in the event of a short circuit.A very fast shutdown circuit could help.Otherwise, for sensitive circuits, you can use other methods independently of the respective power supply, such as clamping diodes to protect against overvoltage and series resistors to protect against overcurrent.

author: nctnico
author_rank: Super Contributor
timestamp: August 21, 2025, 08:17:05 pm
content: Quote from: Martin72 on August 21, 2025, 07:45:41 pmDid you work as an intern at one of the companies I used to work for? This story sounds eerily familiar

author: Martin72
author_rank: Super Contributor
timestamp: August 21, 2025, 08:27:07 pm
content: I have remained loyal to one company throughout my entire professional life, from intern to test field manager. So if you worked for a power electronics company in northern Germany in the early 2000s...

author: Bernd_2
author_rank: Contributor
timestamp: August 22, 2025, 03:20:39 pm
content: Hello,Here is a measurement taken with the Uni-T UDP3305S, 2 x 32 V, 5 A and 1 x 6 V, 2 A.Figures 2 and 3 show the current and voltage curves at 8 V u, 40 mA. Figure 4 shows a comparison at a set voltage of 30 V.The threshold values for rise and fall time for the current are 1% and 99%. At 0% and 100%, the result was distorted too much by the slight ripple in the measurement curve.Best RegardsBernd

author: David Hess
author_rank: Super Contributor
timestamp: August 22, 2025, 11:03:04 pm
content: Quote from: Martin72 on August 21, 2025, 08:07:26 pmSome output capacitance is usually acceptable for a power supply, with about 50 microfarads per amp being typical in a good design. Better designs can operate with a minimum of output capacitance, considerably improving current limiting. The 10 amp design shown below uses 0.022 microfarads per amp and clamps the current error amplifier for faster response.The second example below is a design I have been thinking about which implements clamping for both standard operational amplifiers. I have not thought about the frequency compensation or output capacitance yet, but in theory it could support a low output capacitance.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 23, 2025, 05:03:42 pm
content: Quote from: Martin72 on August 21, 2025, 07:45:41 pmthis is why myself I always disconnect power cables from PSU side at the end - manner I got during 90ties and after some significant money lossesI do not trust even output ON/OFF equipped ones as they have those buttons connected to uC... Only few I worked with had real mechanical ON/OFFAt some companies new engineers are usually smiling or straight laughing when they notice that older colleague has self made "magic box" with switch alike this and LED indicating if it is ON...One laughs untill he first time burns something worth his montly or few months salary then they suddenly have such "magic box"I seen few times more advanced constructions with current metering and circuit breaking (when you are after PSU you will not trigger line RCD so fast or not at all so addtional protection measures too) but those were like few hundred to 2k $ of engineering and parts and what most needs is such switch with LED/bulb indicatorBTWit also makes one more carefull as second problem with leaving some built circuit to later just power on is that someone else may come and play with that PSU or use it for something else changing the values and when you turn it on your first thought wtf it is burning then you see that preset voltage is now 60V / 10 Amps and with constant voltage instead of 3V constant current mode...

author: Mahagam
author_rank: Regular Contributor
timestamp: August 23, 2025, 06:22:02 pm
content: Quote from: kmoonwalker on August 23, 2025, 05:03:42 pmUnfortunately, in this case, you lose the ability to control the power supply via SCPI.This also means that all modern controlled power supplies do not have a mechanical switch at the output.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 23, 2025, 06:27:19 pm
content: Quote from: Mahagam on August 23, 2025, 06:22:02 pmyes and noyou can remotely control that box, tooit is the safety when you power everything on untill the output stabilizes on what you want and not what PSU throws during start upI lost one day at 1999 not only few MCUs on some board but fancy expensive equipment I was trying to fix and the board got totally fried :/

author: David Hess
author_rank: Super Contributor
timestamp: August 23, 2025, 11:51:58 pm
content: Quote from: kmoonwalker on August 23, 2025, 05:03:42 pmOn the Tektronix PS503As that I like so much, the front panel ON/OFF switch controls the reference input into the voltage error amplifiers, so the outputs just decay to zero. When powered on, an RC time constant of 14 milliseconds is applied limiting the rise time. This method would be trivial to do with microprocessor control and a manual backup.Directly disconnecting the output with a mechanical switch or relay, or a power transistor, is *not* a good idea. Inductive leads with such a low impedance can cause considerable ringing leading to overvoltage.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 24, 2025, 01:08:58 am
content: good point but I would need to check how it affects low power low voltage applications - never had problems with using on off switch on 5 and 3,3V systems myself - it may also be that it settles faster than to impact starting MCU or what I worked with years ago had no such issues

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2025, 05:02:50 am
content: Quote from: kmoonwalker on August 24, 2025, 01:08:58 amIntel had a problem with it back when Flash memory required an external high voltage supply for programming. One solution is to switch an existing 12 volt supply to the Flash memory, but this can cause destructive ringing, described here:https://www.analog.com/en/resources/design-notes/simple-surface-mount-flash-memory-vpp-generator.htmlThe ringing can be quashed with a bulk decoupling capacitor at the load, but not all loads may have this.

author: Sorama
author_rank: Frequent Contributor
timestamp: August 24, 2025, 09:36:33 am
content: I recently bought an TTI lineair PS and the thing I hate most is the way the outputs are ‘shut off’.They actually don’t get galvanically get cut off but go into short (measured impedance is around 9 Ohm) while indicating the CC level.I hate it because when you -after pushing the button to shut off the output(s), the voltage rails are shorted so you can’t measure anything without physically disconnect the leads.But that is exactly (one of ) the reason I bought a new PS, just to not always have to disconnect physically the leads.How is that going with your PS?Do they also go into short or do they interrupt the output galvanically ?

author: Bernd_2
author_rank: Contributor
timestamp: August 24, 2025, 12:44:20 pm
content: Hello,Here is some information about various PSUs. Resistances and voltages measured with Fluke 289.1. Uni-T UDP3305S: linear 2 x 32 V, 5A; 1 x 6 V, 3A, 328 wattsPS switched off: 1.8 kOhm at the 32 V output and 334 Ohm at the 6 V outputOutput switched off:32 V output: - 4.4 mV output voltage and 212 ohms6V output: 0.005 mV output voltage and 332 ohms2. Uni-T UDP6932B: SMPS 60 V, 10 A; 200 wattsPS switched off: High-impedance outputOutput switched off: 0.001 mV output voltage and 2.6 ohms3. Voltcraft PS3635: linear 36 V, 35 A; 1260 watts; output relay switched but with significant capacitance at the outputPS switched off: 50 kOhmOutput switched off: 5 mV, approx. 10 kOhm4. Conrad PS2403D: 2 x 40 V, 3 A, no switch for the outputVoltage set to 0: -50 mV, 3 kohm5. WANPTEK NPS605W: 60 V; 5 A, no output switchVoltage set to 0: 50 mV, 2.5 kohmBest RegardsBernd

author: mahi
author_rank: Regular Contributor
timestamp: August 24, 2025, 01:16:05 pm
content: Rohde & Schwarz HMP4040:4-channel power supply with 32V/10A (up to 160W per channel, 384W total)PS switched off: 1.87 kOhm for each channelPS on but outputs switched off: 0.61 .. 0.66 mV, 1.87 kOhm for each channelNote: HMP4040 from before 2017-2018 have a 10 kOhm output resistance.

author: Martin72
author_rank: Super Contributor
timestamp: August 24, 2025, 09:41:28 pm
content: Quote from: kmoonwalker on August 23, 2025, 05:03:42 pmQuite a few power supplies that do not have a mechanically switched output tend to be rather “sluggish” when building up voltage at the beginning, which could be seen repeatedly here.This can have some unpleasant effects, e.g. if the test object to be powered has “simple switcher” circuits to supply the internal circuits.With power supplies like these, I have gotten into the habit of using mechanical switches.First, press the power supply's output button, then use the switch to close the circuit to the consumer.When switching on, the “risk” of too much voltage reaching the consumer due to overshoot is relatively low, as is the case with mechanical switching.I recently purchased 10 power supplies from GWInstek for our department, which have relays at the output—I will test this soon and post their behavior here.

author: BillyO
author_rank: Super Contributor
timestamp: August 24, 2025, 09:49:56 pm
content: I think a lot of the sluggishness comes from them having to deal with a current limit as they power up. If they were just heading to a set voltage, they would be faster.

author: nctnico
author_rank: Super Contributor
timestamp: August 24, 2025, 10:13:27 pm
content: Quote from: kmoonwalker on August 23, 2025, 06:27:19 pmOne major design best-practise to take away from this thread is to always have TVS diodes (or another way to limit the voltage) across supply rails. Especially if a board is powered by an off-board power supply. TVS diodes are cheap and quick to put on a board so the effort and cost is minimal.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2025, 10:55:53 pm
content: Quote from: nctnico on August 24, 2025, 10:13:27 pmWhen I rebuilt my DM502 multimeters, I added TVS diodes to the regulated supply outputs because I was worried about regulator failure damaging irreplaceable ICs.

author: kmoonwalker
author_rank: Frequent Contributor
timestamp: August 25, 2025, 12:54:52 am
content: Quote from: nctnico on August 24, 2025, 10:13:27 pmusually the best way was to have some LM7805 or whatever regulator closer to each chip but there are times when we simply want to start something up or test chip's stability in case we suspect it to be faulty and not on all situations i.e. when we repair something we can modify it just like that with parts at hand - it is easy to need 0,5-1am regulator but 5-10 amps and low dropout ones are usually expensive and not in the box when we need themTVS are also a good way to goanyway one could expect in 2025 that PSU designer will remove such "extra" effects

author: AVGresponding
author_rank: Super Contributor
timestamp: August 25, 2025, 06:55:54 am
content: Quote from: kmoonwalker on August 23, 2025, 05:03:42 pmThe problem with doing this is that it allows any output capacitance to dump current into the load at switch on.