EEVblog #1293 - New NGP800 800W Power Supply - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: March 21, 2020, 04:34:47 am
content: A look at the new Rohde and Schwarz NGP800 800W system power supply. Teardown and a brief play around.Subscribe on library:https://lbry.tv/$/invite/@eevblog:7

author: sibeen
author_rank: Frequent Contributor
timestamp: March 21, 2020, 05:54:01 am
content: *drool*

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: March 21, 2020, 06:02:07 am
content: Dave, let me get the circuit topology right , the unit has a common primary to all four isolated secondary stages . This would mean their is one switchingtransformer with four independent secondary's for each modules?Or is their is a common high voltage primary side with four isolated switching transformers on each module ?Maybe you could have clarified this point on the white board drawing a block diagramThat touch display is "sex on the stick" along with those magnetic coils .How come you didn't test the "sense pins" on each independent output

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 21, 2020, 06:04:19 am
content: The general topology appears to be a single PFC input stage (can't see what style) producing a common HVDC rail (probably around 400V). Each output then has a separate DC-DC isolation and regulation stage.I can't quite make out the exact DCDC stage topology - I doubt it's a resonant type as there are no resonant capacitors and the power level is quite low. The two pairs of gate drive transformer and CT suggest that the transformers operate in parallel. They could be flyback or forward converters? I originally thought the big output inductor would be for a buck converter, but I can't see the associated freewheel diode.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: March 21, 2020, 06:10:18 am
content: Quote from: Phoenix on March 21, 2020, 06:04:19 amThat's what I thought their is something like a 450 DC volt highly regulated high voltage primary rail for all four independent secondary module so you can series and parallel the outputs.Dio-Dee's !

author: KaneTW
author_rank: Frequent Contributor
timestamp: March 21, 2020, 06:48:49 am
content: Man, I love R&S' stuff. I have a HMC8043 and would upgrade to one of these in a heartbeat.

author: prasimix
author_rank: Unknown
timestamp: March 21, 2020, 07:48:18 am
content: Thanks Dave for a great video. To me it's a sort of "reality check" for something that I started few years ago on your forum withEEZ H24005and continue to improve withEEZ BB3. So, it seems that someone in R&H resonate with my ideas when so many things that we added a while ago now become publicly available on their latest device. Perhaps they just followed my path, backed up with multi-million R&D budget. Still, they have a lot to do, and some stuff they are not going to catch up soon, like our ~3 sec boot time (at least it seems that they are running Linux instead of embedded Win). Perhaps they could much easily add MicroPython support ...... or MQTT:.Not to mention that design will not going to be open source any time soon (that include also software on the PC side for GUI editing and SCPI remote control like FOSSEEZ Studio).Anyway, I can say that both H24005 and BB3 are still the only power supply (and more in case of BB3!) that comes with touchscreen well under $1000. Let's see how soon Rigol et al. will catch up.

author: EEVblog
author_rank: Unknown
timestamp: March 21, 2020, 10:47:14 am
content: Quote from: Phoenix on March 21, 2020, 06:04:19 amThere are three large film caps behind the heatsink.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 21, 2020, 11:42:24 am
content: Quote from: EEVblog on March 21, 2020, 10:47:14 amI guess 1 could be the HVDC input decoupling and the other 2 as resonant capacitors for 2 LLCs.Now I'm still looking for 2 resonant inductors - unless the transformers leakages are sufficient - probably quite resonable.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: March 21, 2020, 12:25:33 pm
content: The thing of beauty and joy forever!

author: dr.diesel
author_rank: Super Contributor
timestamp: March 21, 2020, 12:28:38 pm
content: Quote from: KaneTW on March 21, 2020, 06:48:49 amMy most used power supply as well, love it.

author: cgroen
author_rank: Unknown
timestamp: March 21, 2020, 12:35:20 pm
content: I bought a R&S HMP4040 after seeing Dave's review video on it. I'm trying hard to resist this one

author: H.O
author_rank: Frequent Contributor
timestamp: March 21, 2020, 12:58:00 pm
content: Very nice indeed, wouldn't mind being sent one of those out of the blue :-)One UI thing that would irritate the crap out of me is how the menu always seems to return to the top when you "go back", ie leaving you to scroll down in order to continue where you left off.

author: nctnico
author_rank: Super Contributor
timestamp: March 21, 2020, 01:42:22 pm
content: From a previous discussion on an HP 6024A I remember that flyback is the only topology which allows a very wide voltage range. Likely this PSU has a 2 phase flyback converter in order to reduce the ripple. The two current transformers are likely there to sense the current during each switching cycle and shutdown in case of an overcurrent situation.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 21, 2020, 02:03:24 pm
content: Regarding the two pretty symmetrical stages on each channel, perhaps configuring for series/parallel operation? The MOSFET doing the switching? I've seen some very wide voltage range PSUs with that topology.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 21, 2020, 08:16:49 pm
content: Quote from: nctnico on March 21, 2020, 01:42:22 pmI don't think flyback is correct either as I can't see anything that could be a flyback clamp circuit. The power supply has operation down to 0V (as you'd expect from a bench supply). You can't easily do this with an LLC or flyback unless you use some sort of burst mode - which gets quite messy. I'm still wondering if the large FET and inductor form a buck output - but where's the diode?Quote from: Paul Moir on March 21, 2020, 02:03:24 pmThey could be doing series/parallel between the 32V and 64V models with configuration jumpers or smaller PCB changes.

author: nctnico
author_rank: Super Contributor
timestamp: March 21, 2020, 08:46:44 pm
content: Quote from: Phoenix on March 21, 2020, 08:16:49 pmIn the HP6024A they use two switching MOSFETs so the energy (from the leakage inductance) flows back into the supply rails. Look up the service manual for the HP6024A; it has a large section on how it operates.Looking at the video and HP6012A / HP6024A schematics again I'm convinced it is a dual phase flyback converter. The 4 MOSFETs and two identical transformers (identical part numbers!) point towards that.It is interesting that R&S choose to use that expensive current sense resistor. A 3W surface mounted current sense resistor would have done the job but the thermal coefficient is likely to throw the accuracy off.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 21, 2020, 09:30:28 pm
content: Dual switch flyback still requires 2 diodes on the primary as the aforementioned flyback clamp circuit. I can see one 1000v smd on each circuit that appears to go to a ceramic capacitor, if there is another one might be hidden.There are also 2 output diodes for each transformer. They could be in parallel for a flyback.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: March 21, 2020, 09:34:59 pm
content: The above diagram is more of a "push pull " switching design using MOSFETS. I always thought that the fly-back topology was used mainly in CRT televisionin the horizontal output stage, to create high voltage for the anode

author: EEVblog
author_rank: Unknown
timestamp: March 21, 2020, 10:40:50 pm
content: Quote from: Phoenix on March 21, 2020, 11:42:24 amI figured they reused the isolation transformer as the inductor. Neat if you can get away with it.FYI:

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: March 21, 2020, 11:03:08 pm
content: It looks like the output of a class AB (push pull) audio amplifier, with a crossover circuit and T1 is the speaker voice coil, something you would see in a high price car audio amplifierYou would also see a circuit like above as a step up switching power supply in car amplifiers to take the 13.8 battery DC voltage and increase it over 60 volts DC, rail to rail for the audio output stage I would imagine in the power supply shown this video, it does the complete opposite

author: Maxlor
author_rank: Frequent Contributor
timestamp: March 21, 2020, 11:11:17 pm
content: Really nice power supply, but it's 5000 bucks, yowza.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 21, 2020, 11:45:03 pm
content: Quote from: Phoenix on March 21, 2020, 08:16:49 pmYes possibly, but the case I was thinking of they did it on the fly. Sort of like using a relay to hook up different taps on a linear supply. Looking at the specs, I think it fits "under the curve".

author: nctnico
author_rank: Super Contributor
timestamp: March 22, 2020, 12:41:12 am
content: I'm not buying the resonant mode story. For starters resonant mode power supplies are so efficient that at 200W you don't need a heatsink for the MOSFETs (see the demo board from Infineon). Also using exactly the same transformers for both tank circuit and output transformers is highly unlikely. AFAIK often the leakage inductance from the transformer is used for the resonant inductance so you don't need two transformers / seperate inductor (the Infineon demo board only has one transformer and no seperate inductor). Besides that the transformers are way too big for a 200W resonant supply. I've seen >300W resonant power supplies using integrated transformers (E-core ferrite glued to a board and using PCB traces as the windings) over 2 decades ago. Also the current transformers don't look fast enough to deal with cycle-by-cycle current limiting at the typical frequencies of resonant power supplies (and why would it need two?).The capacitors on the board are more likely power supply decoupling capacitors. Again: why would you need more than one for a resonant supply?Look at this picture from the HP6024A (200W switching flyback PSU from the early 80's) and spot the similarities. You can easely identify the switching MOSFETs (top left), transformer (top middle), current sensing transformer (middle, next to the MOSFETs) and rectifier + output filter (top right).It would be interesting to do a further analysis of what R&S actually implemented in this power supply. Also I'm not sure I like the way the NGP800 is built. To me it looks like a nightmare to repair. How are you going to replace any of the parts on the heatsinks? Access is horrible and to me it looks like once a part is unstuck from the thermal tape, a new part will be hard to glue back.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 22, 2020, 01:27:40 am
content: Having mosfet, diodes transformers and cts is normal for every topology. For a dual switch flyback - where are the input flyback clamp diodes? Yes it can recirculate the energy, but you need the diodes! If you can find them it's a good argument.Also with an llc or flyback, how do you get down to zero volts output, with current control? Flyback maybe operate discontinuous, but what fun that would be from a control stand point.I still can't shake the feeling of that extra big inductor doing more than a little filtering. And that big mosfet... Or is that just output enable?The small relay looks to be for selecting sense location, I can't see any series/parallel self configurability.

author: Tek_TDS220
author_rank: Regular Contributor
timestamp: March 22, 2020, 01:38:27 am
content: I don't want to disrupt this discussion on circuit topology, but I'm interested in the ability of this power supply to deliver at least 8 amps (or more?) at 1 volt. Are there other power supplies (even a single channel device) that can do this? I know there are supplies that deliver 10 amps and are capable of regulating at 1 volt, but they shut down when you ask for both at the same time.

author: nctnico
author_rank: Super Contributor
timestamp: March 22, 2020, 01:53:40 am
content: Quote from: Phoenix on March 22, 2020, 01:27:40 amIf you look closely you can spot some devices which look like diodes near the MOSFETs. The flyback diodes don't need to be big since the primary current is relatively low (it also depends on how low the leakage inductance of the transformers is). I think there are also a lot of components on the solder side of the board. I have not spotted the gate drivers for example.QuoteI think the big MOSFET is used as an active load to get to 0V and to pull the output to a lower voltage (discharge the capacitors). The SOA graph looks good enough for that purpose. For an output enable it wouldn't need to be on a heatsink. Also switching the load using a MOSFET leads to a few problems with rush-in currents etc.All in all it would be nice to have some high-res pictures of both sides of the board to be sure.

author: rx8pilot
author_rank: Super Contributor
timestamp: March 22, 2020, 01:55:13 am
content: This one single unit would replace all of my MASSIVE Agilent system power supplies as well as provide a vastly improved user interface.I will seriously consider this unit in the next 6mos. for a specific project. The space savings, performance, and ease of use will likely make the price tag worth it.

author: nctnico
author_rank: Super Contributor
timestamp: March 22, 2020, 02:03:45 am
content: Quote from: Tek_TDS220 on March 22, 2020, 01:38:27 amWhich supplies did you try? I can't imagine why any power supply would have problems delivering 1V at 10A if it is rated for that current.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 22, 2020, 05:54:02 am
content: Quote from: nctnico on March 22, 2020, 01:53:40 amThe gate drive transformers are right next to the CTs and it's easy enough to hide a couple of gate resistors somewhere. The US1M diodes might do the job and there could be stuff on the bottom as there isn't much decoupling I can see around the PIC32. But if it's a flyback why would you need 2 output diodes per channel - simply in parallel?QuoteYes please; it 'should' end the topology discussion.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 22, 2020, 05:56:53 am
content: Quote from: Tek_TDS220 on March 22, 2020, 01:38:27 amThat's a pertient question for the topology discussion too. According to the datasheet this supply can produce/regulate rated current down to zero volts - what topology is capable of that besides a buck? Can a flyback or LLC readily do this (even with an active load)?https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/NGP800_dat_en_3609-1927-32_v0100.pdf

author: EEVblog
author_rank: Unknown
timestamp: March 22, 2020, 10:10:14 am
content: Quote from: Phoenix on March 22, 2020, 05:56:53 amMaybe that extra MOSFET is an LDO?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 22, 2020, 11:50:13 am
content: A surprising point is that there is not much capacitance on the output side of the switcher.The small toroids look like gate drive transformers and current sense transformers. With only 2 gate drive transformers it could be tricky with a full bridge (I don't see 2 well isolated secondary sections). For me this more like points to a 2 phase configuration - with only one large inductor, likely 2 flybacks and the inductor as a common filter after the converter. The challenges for the switcher are more like reasonable fast reaction to load changes and the large voltage range.The FETs may be optimized / good for resonant conversion, but this does not mean they have to be used in this topology only.The extra MOSFET could be something like tap switching - but not sure about that.I would expect the 3 rd heat sink near the output could be a kind of linear LDO stage to get a really smooth and fast reacting output. The specs should tell if this is just a switcher of switcher + LDO.

author: nctnico
author_rank: Super Contributor
timestamp: March 22, 2020, 12:28:25 pm
content: Quote from: Phoenix on March 22, 2020, 05:56:53 amFlyback = buck with a transformer in between. Maybe a better term would be isolated buck converter.

author: Tek_TDS220
author_rank: Regular Contributor
timestamp: March 22, 2020, 01:40:26 pm
content: Quote from: nctnico on March 22, 2020, 12:28:25 pmThanks for the responses. I didn't phrase my question well. I need to run a lot of current through a wire with a cold resistance of ~0.05 ohms. I've tried a couple of powers supplies that should be able to do this, but they have protection circuitry that prevents it. I would love to have the R&S supply, but I can't justify the cost.After thinking about it more, a beefy MOSFET with a big heat sink would solve my problem. I'll try that.

author: cgroen
author_rank: Unknown
timestamp: March 22, 2020, 01:51:25 pm
content: Quote from: Tek_TDS220 on March 22, 2020, 01:38:27 amI just tested my R&S HMP4040, that one does this without problems (I was using remote sense also)

author: EEVblog
author_rank: Unknown
timestamp: March 22, 2020, 10:16:02 pm
content: Someone on the Youtube comments just mentioned this is likely a Phase-Shifted Full-Bridge, and I suspect they might be right.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 22, 2020, 10:56:15 pm
content: Quote from: EEVblog on March 22, 2020, 10:16:02 pmIt matches the components better if one of the transformers is the series inductor. But, if it is a full bridge primary why do they have 2 CTs, and 4 diode on the output? It would be a lot easier to have a single CT in the transformer path than say one in each phase leg and have to OR their outputs.

author: nctnico
author_rank: Super Contributor
timestamp: March 22, 2020, 11:34:34 pm
content: Quote from: EEVblog on March 22, 2020, 10:16:02 pmI doubt it. It wouldn't explain the need for two transformers and why the switching MOSFETs are on a big heatsink. Unless they run them in parallel and leave one out in the 400W version but it would leave the question why there are two current transformers. However the first question to answer is whether the topology supports a wide output voltage range. So far most switching variable voltage output power supplies I have taken apart uses a flyback / buck topology. In a forward converter-ish design like the Phase-Shifted Full-Bridge the output inductor is the problem to make a wide range of output voltages possible. But it is not impossible. The very cheap PSUs use a forward converter design. If it is a forward-converter design then I suspect they run two identical transformer / diode sections in parallel on the 800W version and one section in the 400W version. However, if it is a forward converter design I would expect an extra filter inductor because the large toroid would be the inductor used to charge/discharge the energy from the transformer. In a lab PSU I would expect some extra filtering (but this could impair transient behaviour).It would be nice if you could take the power board out and take pictures of it. I think there are quite a few components on the solder side (including gate drivers).

author: EEVblog
author_rank: Unknown
timestamp: March 23, 2020, 02:33:03 am
content: Quote from: nctnico on March 22, 2020, 11:34:34 pmDoesn't look that easy, but might give it a go some time, just not right now.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 23, 2020, 02:40:32 am
content: Quote from: nctnico on March 22, 2020, 11:34:34 pmYes please!I'm not sure what you're missing in terms of gate drives, however. The gate drive transformers are next to the CTs. And you could hide a couple of gate resistors on the other side of the heatsink.

author: ignilux
author_rank: Unknown
timestamp: March 23, 2020, 03:08:25 am
content: Quote from: EEVblog on March 23, 2020, 02:33:03 amWtf else do you have to do right now? This is your full-time job and that !@%$# virus has us all locked up inside with nowhere to go and nothing to do. I was so bored earlier that I actuallycleaned my bench. Do you have any idea what it takes to get me to do that?!

author: Messtechniker
author_rank: Frequent Contributor
timestamp: March 23, 2020, 06:56:36 am
content: Quote from: dr.diesel on March 21, 2020, 12:28:38 pmSame here.

author: nctnico
author_rank: Super Contributor
timestamp: March 23, 2020, 10:29:23 am
content: Quote from: Phoenix on March 23, 2020, 02:40:32 amUsually there is some additional circuitry together with gate drive transformers.

author: EEVblog
author_rank: Unknown
timestamp: March 24, 2020, 07:03:29 am
content: Quote from: ignilux on March 23, 2020, 03:08:25 amTake care of the kids (they are now home from school full time)Move into the new lab.Business stuff.Packing and shipping (my logistics person is in lockdown).And, you know, videos of countless other stuff that is on the back burner, and ones that, you know, may interest me more than a THIRD video on this power supply.In case you haven't looked at the view stats, that last video wasn't exactly popular, in fact my worst performing one in a long time.

author: nctnico
author_rank: Super Contributor
timestamp: March 24, 2020, 08:29:11 pm
content: Quote from: EEVblog on March 24, 2020, 07:03:29 amKarma in action for not taking it apart completely