EEVblog #549 - Rigol DP832 Lab Power Supply Followup

[Cdngreybeard]

I checked my replacement DP832A and it still has the power on voltage spikes.  My question to the
Forum is, do your other power supplies also exhibit power on spikes?  I own a Hameg triple power supply that also shows power on spikes.

[sprocket]

Some times I really wonder.

Why do some people insist on a 300dollar rigol PSU to be at the same high standard as a +1300 dollar agilent PSU?

Sure this PSU had a bad design flaw. BUT THEY FIXED IT. Many companies wouldn't give a flying toss about it, sweep it under the rug and fix it on a later board revision, and just the fact that rigol have acknowledged this design fault and fixed it, proves to me they are serious about becoming a reputable brand company, and not just the regular copy-paste knock off shit products that constitutes 90% of everything that comes out of china. Agilent, Tektronix, lecoy etc. etc. needs to keep an serious eye out for rigol. I remember when I was a kid in the 80's when electrics that came out of Korea and Taiwan was utter garbage, I dont think any one thinks that any more.

I for one had no problem what so ever in buying the rigol DP832 after they changed the lay out for the LM317. Sure it has a few quirks you probably wouldn't see in a +1300 dollar agilent PSU, but for hobbyist use and even for most small companies, schools and universities a PSU like this is a no brainer. There is nothing on the marked that I have seen that gives you this much bang for the buck as this PSU does.

[alm]

There's no indication that Rigol would have fixed the existing instruments if Dave didn't complain about them publicly. The old supplies were still in the distribution channels, even though the flaw appeared to have been discovered at Rigol. So it seems that they would also have swept it under the rug and silently released a new version if not for Dave. From the forums it seems that communication about replacement of existing power supplies is still quite poor. Other forum users reporting issues (DG1022 software support, some DM3068 issue) have generally been ignored or brushed off. Korad also fixed their power supplies after Dave's damning review. I think this is more a matter of the marketing department figuring that Dave complaining about their product is bad publicity than genuine customer service.

People often consider the new Rigol scopes to be close to or even in the same league as the Agilent scopes. This is clearly not the case for power supplies, although they might offer decent bang/buck for hobbyists.

[bronson]

I love how Dave wonders "is that hot?" and reaches right in and grabs the heat sink.  You'd think he'd know better by now.  I know I've done that a bunch...  "hm, is current flowing in thYEAOUCHHH!!  Yes.  Yes, it is.  BRB bandaid."

I guess there's still hope for me.  I did finally learn that about catching falling soldering irons.

[Jon86]

What really grinds my gears is all that output capacitance. Imagine if you had something that you were running on constant current at 10mA, then you disconnect it and connect it again, and all that cap just entirely discharges into the load... 

[alm]

That's actually pretty standard and something to be aware of in all bench supplies, although well designed power supplies tend to be stable and have reasonable noise levels with smaller output caps. Does anyone remember the capacitance from the teardown or calculated it using I/C=dV/dt? I believe that TTi manuals do a good job of explaining this issue.

[robrenz]

That is a 2 edged sword, what about full current transient response without the output cap?  Some old hp supplies have the output cap connected thru rear terminal straps so you can unstrap the cap when you don't want it.

[sync]

What really grinds my gears is all that output capacitance. Imagine if you had something that you were running on constant current at 10mA, then you disconnect it and connect it again, and all that cap just entirely discharges into the load... 

Use a constant current source then.

[alm]

A fast regulation loop with fast settling times can have good transient response without huge caps. Bob Pease published the design of a power supply without any caps on the output for this purpose. The basic problem is that a good bench supply is a voltage and a current source in one. An ideal voltage source has a zero output impedance, so caps improve the voltage source by reducing the output impedance. An ideal current source has an infinite output impedance, so caps degrade the current source. Most bench supplies, especially the cheap ones, are better voltage sources than current sources.

[jahonen]

I can't understand why it is so difficult to do a proper fix for such a simple issue; an obvious one is that if the output voltage goes just into MCU & mostly digital stuff, then why not just put a switch-mode regulator and be done with it. Instead of putting that enormous heatsink. I also noticed that there are traces running just below the heat sink, I can't see if there are any free space between the PCB traces and the heat sink, but I afraid that only insulator between those traces and heat sink is just the solder mask. If that is the case, it is only matter of time when solder mask gives up and heat sink produces a short in those traces. Solder mask should not be used as an electrical insulator.

I can understand that the efficiency does not matter, but in this case it causes components to run unnecessarily hot. And regarding to potential EMI effects, I think that they are quite often easier to take care than the heat problems if you take the time to think about it. Besides, i.MX CPU already contains an internal switcher (I don't believe that they run it with internal LDO).

Regards,
Janne

[sprocket]

yea well. SMPS PSU have their use. But they also have downsides, so depending on your application you have to choose. I know a liniar is not very efficient, but I don't care, I want some thing that is 100% noise free.

One of the places I worked when I was in the army, we gave up on using SMPS pus to drive the VHF and HF radios when we ran tests on them. All the SMPS based PSU's we had simply put out to much noise for us to actually make decent testing on the radio's. One particular Agilent SMPS psu thats actually still in production totally blanked out the radios aroudn the 42-43MHz range. So we dusted off our old liniar PSU's and voila problems solved.

[EEVblog]

Who would have guessed that they fail to calculate the size requirement for that heatsink, twice.

Yes, it's pretty silly.
The first time they realised it themselves (or had someone else find it?) and changed from the small one to the larger black anodised one. Then due to my video they doubled the size again with the same footprint.

[jahonen]

yea well. SMPS PSU have their use. But they also have downsides, so depending on your application you have to choose. I know a liniar is not very efficient, but I don't care, I want some thing that is 100% noise free.

But then, the whole thing must be considered as a whole, not just the regulator that powers the processor. There is a i.MX processor running on 100's of MHz along with an internal switching regulator, DDR memory and wide parallel bus going into LCD, I'd think that is already quite far from 100% noise free analog stuff anyway. Small switch-mode regulator doesn't change EMI properties that much anymore. It would be a different thing if there weren't any digital electronics in that thing.

Regards,
Janne

[sprocket]

yea well. SMPS PSU have their use. But they also have downsides, so depending on your application you have to choose. I know a liniar is not very efficient, but I don't care, I want some thing that is 100% noise free.

But then, the whole thing must be considered as a whole, not just the regulator that powers the processor. There is a i.MX processor running on 100's of MHz along with an internal switching regulator, DDR memory and wide parallel bus going into LCD, I'd think that is already quite far from 100% noise free analog stuff anyway. Small switch-mode regulator doesn't change EMI properties that much anymore. It would be a different thing if there weren't any digital electronics in that thing.

Regards,
Janne

granted, MCU's are obviously not "noise free", but MCU's dont radiate any thing of significance, not in the real life cases that I have delt with any ways. Where as a 30amp agilent switcher blanked out an entire work shop. And bare in mind this agilent unit is still being made if I recall correct.

[ZeroAviation]

Yes, it's pretty silly.
The first time they realised it themselves (or had someone else find it?) and changed from the small one to the larger black anodised one. Then due to my video they doubled the size again with the same footprint.

Sorry if I missed this answer somewhere. I did read all of this thread.

Is the larger black anodised one still ok? I measured 63C at 25C ambient on the side of the heat sink with the fins. It was powered on for about 20 minutes. I should also mention it was with the case on, I stuck my thermocouple through the holes.

Thanks!
-Matt

[Rigby]

Yes, it's pretty silly.
The first time they realised it themselves (or had someone else find it?) and changed from the small one to the larger black anodised one. Then due to my video they doubled the size again with the same footprint.

Sorry if I missed this answer somewhere. I did read all of this thread.

Is the larger black anodised one still ok? I measured 63C at 25C ambient on the side of the heat sink with the fins. It was powered on for about 20 minutes. I should also mention it was with the case on, I stuck my thermocouple through the holes.

Thanks!
-Matt

http://www.fairchildsemi.com/ds/LM/LM317.pdf

If I remember from the video, that LM317 is dissipating 7W.  According to the datasheet, if I'm reading it correctly, that means the physical package will be 35°C cooler than the junction temperature.  The maximum for the junction is 125°C, so take your 63°C + 25°C to get the junction temp = 88°C.  That's well under 125°C, so you're good.

PLEASE correct me on any of this if I'm wrong.  I'm still very much a newbie to this.

EDIT: oh, you're measuring the heatsink.  Measure the LM317 itself to get a better reading.

[Zbig]

I checked my replacement DP832A and it still has the power on voltage spikes.  My question to the
Forum is, do your other power supplies also exhibit power on spikes?  I own a Hameg triple power supply that also shows power on spikes.

I have a Siglent SPD3303S. It had no power-on spikes on neither of its two main 0-30V channels 1 or 2 but exhibited a "hard power-on" (with a mains switch, not with a soft-enable switch) spike on auxiliary 2.5V/3.3V/5V channel 3. User FrankBuss of this forum has worked with the support and they've provided a fix self-repair solution which Frank described here: https://www.eevblog.com/forum/testgear/siglent-spd3303d-review/msg299246/#msg299246 Reportedly, they've revised the PCB already.

[Oracle]

Too many issues on this thing, don't worth buying.

[Rigby]

Too many issues on this thing, don't worth buying.

I don't think that's true at all.  Every bit of test gear will have something that any given user won't like.

Just be aware of the issues your equipment has and you'll be fine.

I'll be buying one of these soon.  I am aware of the issues, and given the price and features, this is a pretty awesome power supply.

[madires]

Too many issues on this thing, don't worth buying.

I don't think that's true at all.  Every bit of test gear will have something that any given user won't like.

Just be aware of the issues your equipment has and you'll be fine.

I'll be buying one of these soon.  I am aware of the issues, and given the price and features, this is a pretty awesome power supply.

Yep, that's the point! As long as there's no real show stopper, the price is fine and you know about limitations and smaller issues you can buy it without any worries. If you've got a delicate circuit connect it to the PSU after powering it on. Also follow the wiring recommendation for ch2 and ch3 regarding the interconnected ground and current sensing. I would be more concerned about the reset issue if it's not fixed by fixing the voltage regulator overheating.

[Fabio]

Any news on the reset and the power-on (voltage spikes while output is disabled) issues?

I'm also curious about the reset issue...  Has it been fixed with the new revision?

[Rigby]

Any news on the reset and the power-on (voltage spikes while output is disabled) issues?

I'm also curious about the reset issue...  Has it been fixed with the new revision?

Yes, the spontaneous reset is fixed.  The heatsink was the remedy for that.  The LM317 was overheating, shutting down, causing the scope to reboot.  The larger heatsink prevents overheating, therefore the regulator does not shut down, therefore the logic whose voltage is supplied by that regulator does not reset.

All of this information is in the videos.

[jrgandara]

I´m looking for a new PS for my bench and, in general, I liked this DP832. Obviously those circular keys are ridiculous, but the features and the display looks very nice. But 42 cm deep is too much for my bench. Why so deep?

Two questions:

Any other option with similar features and maximum 32cm deep?

What is the model or where to buy this temperature sensor Dave uses in his Fluke? I have one Fluke 187 and would be nice to have this probe.

Thank you!

[dr.diesel]

Any other option with similar features and maximum 32cm deep?

I bought this mostly because of it's shallow depth:

https://www.eevblog.com/forum/testgear/gw-instek-gpd-4303s-4-channel-ps-review/

[Rigby]

I´m looking for a new PS for my bench and, in general, I liked this DP832. Obviously those circular keys are ridiculous, but the features and the display looks very nice. But 42 cm deep is too much for my bench. Why so deep?

Two questions:

Any other option with similar features and maximum 32cm deep?

What is the model or where to buy this temperature sensor Dave uses in his Fluke? I have one Fluke 187 and would be nice to have this probe.

Thank you!

It's a simple K-type thermocouple with a multimeter adapter.  http://www.adafruit.com/products/270?gclid=CMDdgMyK-7oCFcZDMgodqlIAsQ