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Is Rigol DP832 output voltage spikes when unit is turned on an real problem?
Posted by Rene on 04 Feb, 2015 18:58 -
Hello,
Based on what I have been reading, it appears that the Rigol DP832 output voltage spikes that occur when the unit is turned on is a well-known issue that has been known for a while (at least for a year and a half from the time I am posting this).
And yet, it looks like Rigol has not address the issue and units continue to ship with the problem (at least to my knowledge). That said, I am going to assume that this particular issue is not a problem at all since I am pretty sure that Rigol would have fixed the issue by now if this was a critical issue.
My problem is that I am new to all these so I have very limited knowledge about electronics to know if my assumption is correct or not. So my question is: Am I correct in assuming that the spike issue is not an issue at all?
By the way, I realize that I can always unplug the power supply from my circuit before turning the unit on to avoid the issue but chances are that sooner or later I will forget to do that and quite honestly, this is something I don’t want to have to worry about if I have to pay $520 dollars for the unit (after tax and shipping).
in case it helps, here is the video link that talks about the issue: http://youtu.be/IaWgF1SORkk?t=37m7s
Thanks.
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Here are dp832 1st and 2nd channel during turn on. 3 records of switching it on.
I see some spikes, sometimes it's positive, sometimes negative, in a range +- 0.5V.
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it's only an issue if it's an issue for you
In other words... I see a small spike as well. Most of the stuff I work on is 12V, and I always design for at least 16V, and almost always for transients beyond that.
The very rare times I do something else would be directly powering a 5V or 3.3V circuit during debugging. And in pretty much all those cases, I wouldn't have the PSU on first... but even if I did, the 0.5V spike wouldn't fry a 3.3V or 5V MCU, especially since the chips would be decoupled.
So for me, the voltage spike issue is a non-issue.
For you, or for others... it depends on their requirements. Having said that, I have maybe 8 or 10 PSU's from Agilent, Sorensen, Chroma, Philips, Fluke, BK and some others, and my go-to PSU is the Rigol. It's the most versatile, easiest to use and most capable. And some of my "nicer" PSU's have spikes on turn on also... some a lot worse than the Rigol (some a LOT LOT worse). So it's not something specific to Rigol, maybe more specific to this class of PSU. -
Transient voltages of either polarity below one Ube (~0.6 V) are usually no problem for the great majority of circuits (including all kinds of logic families I am aware of).
That being said I don't like transient output voltages on turn on/off anyway. A commercial lab supply I have here generates about +-0.8 V on turn on, while my own supplies do not generate any transient on power on at all — can't see it on the scope, must be below noise floor, i.e. less than 0.4 mVpp. I feel bold enough to say that this is a non-issue in any properly done lab supply design.
When I first set out to build my first lab supply I ran about incredibly many designs, which fail in these regard, sometimes horribly. Including designs which would essentially discharge the filter cap into the load when they are de-energized. Even some commercial lab supplies (there were supplies from a German brand, for example, that exhibited this behaviour) do this, which I think is completly ridiculous!
There are also some designs around which are unable to control output voltage in certain conditions on power-up, leading to similar effects.
And then there's the lot of designs with massive overshoot, poor regulation, high noise, inherent instability and so on. I really have the feeling that (numerically!) most lab supply designs are just complete crap. -
The glitching is very unpredictable. The vast majority of the time, it is at the 0.3-0.4V level and very short, but occasionally, it is much higher.
Here is shot taken with a 34461A in fast acquisition mode (~1000Hz) using Sparky's program. The DMM is in the 10V range and Hi-Z.
The peak is >7V and lasts for about 300ms.
Note: I did not manage to get more than a 500mV glitch on the scope, that's why I moved to the DMM. I don't know if I caught something on the DMM just for statistical reason (anything >0.4V is very rare to begin with) or if there is something specific to the DMM setup (i.e. because the inputs are not grounded unlike the scope or because of the Hi-Z input mode).
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Mine is pretty repeatable and I'm personally not too worried about it.
The following captures where made with a banana-to-BNC adapter and coax straight to the scope input. There's one capture with no load on the supply and one with the 50ohm input termination of the scope enabled.
This is a tricky experiment. The 1.7V output (at no load) lasting for 250ms is coming from the DP832 for sure but the short spike prior to that I'm not too sure about. I can leave the DP832 off (or on for that matter) and get spikes much larger than that to seem to appear on the output by turning on/off other equipment....
Sorry about the on screen messages in the second capture, USB stick had a firmware file on it.
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Why this would be an issue when most PSUs - even better brands - have a similar behavior?!
Spikes when powered on it's not a dp832 only issue. -
Why this would be an issue when most PSUs - even better brands - have a similar behavior?!
Spikes when powered on it's not a dp832 only issue.
Well except that most cases when this happened with better brands have been fixed in later revisions. And it's definitely not an issue *most* lab supplies have, but only very few.
Also, "XXX is not a YYY only issue" is a kinda crooked argument. It's a damn lab supply, it has to behave, even the cheapest wall-warts get this right. -
Why this would be an issue when most PSUs - even better brands - have a similar behavior?!
Spikes when powered on it's not a dp832 only issue.
Well except that most cases when this happened with better brands have been fixed in later revisions. And it's definitely not an issue *most* lab supplies have, but only very few.
Also, "XXX is not a YYY only issue" is a kinda crooked argument. It's a damn lab supply, it has to behave, even the cheapest wall-warts get this right.
That's not true at all.
I have quite a few PSU's that produce spikes at turn-on, and the suggestion that the DP832 is doing something worse than "the cheapest wall-warts" is silly. My PSU's that produce turn-on spikes are not all early revisions... my Agilent and Sorensen supplies are years into the model runs and produce spikes at start-up. -
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Well except that most cases when this happened with better brands have been fixed in later revisions.
Can you write down a couple of models where this "issue" has been fixed?
Aim-TTi instruments are definitely NOT cheap or crap PSUs, but my PL303 (single channel 30V 3A at € 389,00) has a voltage spike when powered on. It's on the market since years and still has not been fixed in the new releases.QuoteAnd it's definitely not an issue *most* lab supplies have, but only very few.
Something that I was taught many years ago from technicians and friends is to follow the general rule to NOT have anything connected to the PSU before it has been powered on.
Do you state that the lab grade HP PSUs doesn't have this "issue" when powered on?
And did you try personally the wall-warts PSUs to see if they don't have spikes when plugged in? I think you could be surprised from the results.QuoteI have quite a few PSU's that produce spikes at turn-on, and the suggestion that the DP832 is doing something worse than "the cheapest wall-warts" is silly. My PSU's that produce turn-on spikes are not all early revisions... my Agilent and Sorensen supplies are years into the model runs and produce spikes at start-up.
Exactly! -
Ok, yes, there are wall-warts that do this, mostly bad SMPS designs. Older transformer based wall-warts are either unregulated or have something like an 78xx, so don't have this issue. The majority of SMPS wall warts I've seen so far did exhibit a bit of overshoot on turn on, but are okay otherwise. But yes, of course, there are wall warts around that are horrible in many ways.
I know that Hameg once built a few supplies that had this issue. People complained, they fixed it. And they rightfully complained.
I've worked with a few HPs, mostly older ones, never saw anything like that. Simulated many of their designs (yes, with focus on stability and turn on/off behaviour), built two of them, no spikes. And seriously, this is so simple to avoid completely with a proper design, it's just ridiculous to argue that "this is normal and can't be fixed".
I attached a scope screen grab of my version (different output values and power transistors, otherwise identical) of the E3630A. The design of this supply is used by HP for a long time, for example in the 6236B and a few others. It's one of their two main designs for bench top, pot-controlled supplies. I challenge everyone to point out the spot where I turned the mains on. Output switch was on, volts pot down to zero.
/edit: Note: I generally don't work with SMPS lab supplies on my bench and worked only once with a 19" high power SMPS, so I don't know if my remark that this is easy to fix applies to SMPS as well, however, for linear (at least last stage linear) supplies this is easy to fix. If this should really be common with SMPS lab supplies it's one more argument against them, imho.
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Ok, yes, there are wall-warts that do this, mostly bad SMPS designs. Older transformer based wall-warts are either unregulated or have something like an 78xx, so don't have this issue. The majority of SMPS wall warts I've seen so far did exhibit a bit of overshoot on turn on, but are okay otherwise. But yes, of course, there are wall warts around that are horrible in many ways.
I know that Hameg once built a few supplies that had this issue. People complained, they fixed it. And they rightfully complained.
I've worked with a few HPs, mostly older ones, never saw anything like that. Simulated many of their designs (yes, with focus on stability and turn on/off behaviour), built two of them, no spikes. And seriously, this is so simple to avoid completely with a proper design, it's just ridiculous to argue that "this is normal and can't be fixed".
I attached a scope screen grab of my version (different output values and power transistors, otherwise identical) of the E3630A. The design of this supply is used by HP for a long time, for example in the 6236B and a few others. It's one of their two main designs for bench top, pot-controlled supplies. I challenge everyone to point out the spot where I turned the mains on. Output switch was on, volts pot down to zero.
/edit: Note: I generally don't work with SMPS lab supplies on my bench and worked only once with a 19" high power SMPS, so I don't know if my remark that this is easy to fix applies to SMPS as well, however, for linear (at least last stage linear) supplies this is easy to fix. If this should really be common with SMPS lab supplies it's one more argument against them, imho.
You can read through the thread again and you will see that nobody has said "this is normal and can't be fixed" - so arguing against that is the very definition of a straw man argument.
It seems you also accept that the prior statement of "even the cheapest wall warts don't do this" was incorrect.
I am sure you don't own the DP832, and what I can't understand is why you seem to have such hatred for it? I mean... I don't really like McDonalds fish sandwiches... but I don't walk into McDonalds and tell them that their fish sandwich is total shit, or go up to customers eating them and say "ewwww! That is so disgusting! It's sooo easy to cook real fish!". I don't get the motivation behind non-owners apparent angst towards Rigol?
FWIW, I did a Google search on Hameg power supply overshoot, and nothing came up about an issue that was later resolved.
The fact that my Agilent, Sorensen, Philips, Fluke and some other (cheaper) PSU's have overshoot to varying degrees (some of them much, much worse than the DP832) tells me that this isn't something specific to Rigol. But I've never seen a thread bashing Agilent over this issue, despite me having to Agilent PSU's that do it (one worse than the DP832).
The OP asked whether the spikes are a real problem and I think the answers given were fair. In most cases, no, it's not a real problem. Everyone knows you don't leave your device connected to the output when you switch a PSU on. Everyone knows that because overshoot is something that a wide range of PSU's have exhibited for many years. Yet people act like the DP832 is the only PSU ever to do so.
Just don't get the angst over this specific PSU from this specific company. It's really like what you see on audiophile forums if you dare suggest that regular copper cables are just fine.
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I am sure you don't own the DP832, and what I can't understand is why you seem to have such hatred for it? I mean...
I'm sorry if my posts made an impression like hatred, I absolutely don't hate Rigol or their devices, as far as I know they have great value for money. I sometimes get a bit energetic in discussions, so sorry again if I offended someone, I did not intend to
The Hameg issue is buried somewhere in the mikrocontroller.net forums iirc. -
So you people are saying that all these expensive, so-called "lab grade" bench power supplies can't even do something simple like turn on the power in a controlled manner? Spikes and over-shoot are normal? Seriously? And here I thought the two HP power supplies I've gotten off eBay were defective.
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My HP 6653A's spit out about 100mV of spurious noise on startup for a very brief about of time.
I will say that Rigol is making their way into test and measurement by being the cheapest option that can still get something useful done. Some of their gear may be passable but they have nothing that I would bet my business on. For a hobby you get to choose your battles, price or performance.
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Tonight I watched several of Dave's older videos where he reviewed power supplies (B&K, Jaycar, Rigol, and more). In every video he stressed the importance of, and looked closely at, turn on performance (spikes, overshoot, etc). The impression I got was that this is an undesirable behavior and to be prevented/avoided. I tend to agree. I would think more than a half volt overshoot/spike is probably not something you want, ever.
It doesn't seem like this is something to be considered normal or acceptable. -
No one says it should be considered normal. It's only a behavior that many PSUs have, that is known from many years from technicians and you have to deal with. It's NOT a Rigol esclusive issue.
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The potential spike issue with the DP832 occurs when you turn the supply on/off with the electro-mechanical mains switch.
It does not occur when you enable/disable the actual output(s) using the output on/off. If I'm not mistaken it's quite well behaved when using the output on/off buttons but I'm sure someone will be able to come with a certain test condition that makes it overshoot or whatever and call it total and utter crap based on that.
And again I'd like to point out that I can make my scope appear to capture large high frequency spikes at the DP832 output by switching on/off equipment nearby. That doesn't mean the spikes are actually there. So although part of the issue is "generated" by the DP832 when you switch it on (with the power switch) you can't be certain all of what you see is actually there - which I believe Dave has shown in a couple of the videos (common mode noise etc).
Is the DP832 free of issues? Of course it's not but neither are most other stuff.