Author Topic: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown  (Read 20114 times)

0 Members and 1 Guest are viewing this topic.

Online nctnico

  • Super Contributor
  • ***
  • Posts: 16712
  • Country: nl
    • NCT Developments
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #25 on: September 19, 2017, 03:20:46 am »
My big problem is, if Dave is correct, the use of de IRFP250 Mosfet, this Mosfet is NOT DC specified!
I know there are 6 of them, but it gives me the creeps.
I do NOT trust the SOA of this device...
That was my initial thought too but then I remembered Agilent/Keysight is using similar MOSFETs (like IRFP240 / IRF640) in their DC loads. It is not all bad but choosing the right MOSFET for a DC load isn't trivial.
« Last Edit: September 19, 2017, 03:24:44 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline schopi68

  • Regular Contributor
  • *
  • Posts: 123
  • Country: de
    • My stuff page
 
The following users thanked this post: kony

Offline IanMacdonald

  • Frequent Contributor
  • **
  • Posts: 944
  • Country: gb
    • IWR Consultancy
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #27 on: September 19, 2017, 03:41:18 am »
The modified SOA consideration only seems to apply at relatively high voltages. The datasheet for the IRFP250  says 'SOA is power dissipation limited' which I would assume means that derating is not required.  :-//

A point worth noting about power ratings which IXAN0061.pdf mentions, is that case-to-device temperature differences can change extremely quickly, of the order of tens of milliseconds. In other words, the chip has an extremely small thermal inertia. Thus, a sudden surge in dissipation can blow an already-hot device even though it did not last long enough to warm the heatsink measurably, and was not over the device's specsheet rating @25C.  :wtf:
« Last Edit: September 19, 2017, 03:43:22 am by IanMacdonald »
 

Offline NANDBlog

  • Super Contributor
  • ***
  • Posts: 4225
  • Country: nl
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #28 on: September 19, 2017, 03:52:12 am »
Hi IanMacdonald


Download this PDF: http://www.ixys.com/Documents/AppNotes/IXAN0061.pdf
Look @ page 8 figure 10 tipical switching Mosfet, <= Electro-Thermal Instability Boudary
Look at the dashed line and see the horror...

Kind regards,
Blackdog


PS

My Datasheet is from International Rectifier, but Fairchild shows some DC SOA, ST also  ;)
I am well aware of the SOA, FBSOA and other sizing of FETs. I used SOT227 FETs, where they were required. They do 500W each with enough cooling. I also used FETs with and without DC in the datasheet in DC. They work, you just need to select the right one, and make sure they work. The IRFP250 is a solid choice for a DC load. It is used in other DC loads. It is used in audio amplifiers. It has been used for a long time. I personally did not test it, but judging by the amount of circuits using them in DC, it is probably safe.
The instability of the DC load:
It is certainly not trivial to tune the analog parst in these circuits, I know it first hand. Especially, if you have a lot of constrains, like frequency response and rise and fall times. It doesnt help, that it has to be able to do 1mA and lots of amps with the same parts. If you see these kind of oscillations, provide feedback, they will probably do a revision.
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 5511
  • Country: de
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #29 on: September 19, 2017, 04:23:55 am »
Most data-sheets for the IRFP250 don't specify DC operation, however this per se does not say it can not work. I have seen a Fairchild data-sheet that  actually did specify DC operation, even over the full range. However I am not sure it was the IRPF250 or IRFP250N.

The IRFP250 was a common type used in many audio amps. So it is not such an unusual choice, though more a cheap one. I would not worry so much about 40 A at low voltage (e.g. 5 V) but if at all with 150 V at 1 A. Turning off with a inductive source, could cause trouble - so some extra reserve on the voltage side would be good. I doubt they would use two FETs in a cascode mode each.

Why do they have 2 current ranges if there is only one shunt ? They can't use just 1 or 2 of the power stages - as even 4 A would be too much power at 100 V.

The other slightly odd thing is that I don't see high power resistors for current sharing.

Having the amplifiers lasered off for the amplifiers is really strange - I won't expect anything so special with this. The quality of the current reading is more limited by the shunt quality.
 

Offline Avacee

  • Supporter
  • ****
  • Posts: 293
  • Country: gb
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #30 on: September 19, 2017, 04:29:34 am »
When DC load designs have been mentioned in the past the experts here usually suggest having a resister per MOSFET and individual feedback otherwise one MOSFET ends up taking all the current and suffering thermal runaway.
I couldn't see anywhere on Dave's video individual resistors so are all the MOSFETs fighting with each other or are Rigol solving the runaway issue?
Or am I showing my newbishness and a lack of understanding and 1 resistor with multiple MOSFETS is actually fine?
 

Offline NANDBlog

  • Super Contributor
  • ***
  • Posts: 4225
  • Country: nl
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #31 on: September 19, 2017, 04:42:58 am »
When DC load designs have been mentioned in the past the experts here usually suggest having a resister per MOSFET and individual feedback otherwise one MOSFET ends up taking all the current and suffering thermal runaway.
I couldn't see anywhere on Dave's video individual resistors so are all the MOSFETs fighting with each other or are Rigol solving the runaway issue?
Or am I showing my newbishness and a lack of understanding and 1 resistor with multiple MOSFETS is actually fine?
No, you should have 1 resistor per FET. It is probably under the heatsink. Or bottom side. You see the isolation slots? So for sure, the trace from the Drain has to go under the heatsink. And there is a double opamp per FET pair.
 
The following users thanked this post: Avacee

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9510
  • Country: 00
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #32 on: September 19, 2017, 05:36:54 am »
My big problem is, if Dave is correct, the use of de IRFP250 Mosfet, this Mosfet is NOT DC specified!

How can a MOSFET not be DC specified?

I've yet to see a MOSFET that can switch AC. :popcorn:

« Last Edit: September 19, 2017, 05:39:25 am by Fungus »
 

Offline MBY

  • Regular Contributor
  • *
  • Posts: 131
  • Country: se
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #33 on: September 19, 2017, 05:43:48 am »
Nobody noticed the "FERQ" value instead of "FREQ" in the tran-menu? Software feels like beta...
 

Offline blackdog

  • Frequent Contributor
  • **
  • Posts: 569
  • Country: nl
  • Please stop pushing bullshit...
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #34 on: September 19, 2017, 06:04:00 am »
Hi,


Its like Kleinstein explaned, the shit happens if there are high voltages on de electronic load.
You can see it also in the document i refered to, there are no problems in the low voltage range.

Hi Fungus
How can a MOSFET not be DC specified?
Sorry i'am a Dutch dyslexic monkey, i do my best to make it so understandable as posible  :D
This load is specified for 150V! so the SOA is realy important at these voltages.

Kind regards,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Online nctnico

  • Super Contributor
  • ***
  • Posts: 16712
  • Country: nl
    • NCT Developments
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #35 on: September 19, 2017, 06:17:40 am »
When DC load designs have been mentioned in the past the experts here usually suggest having a resister per MOSFET and individual feedback otherwise one MOSFET ends up taking all the current and suffering thermal runaway.
I couldn't see anywhere on Dave's video individual resistors so are all the MOSFETs fighting with each other or are Rigol solving the runaway issue?
I'd get the service manuals for the Keysight N3304 DC load module. This has full schematics and from a functional point of view it looks much like this Rigol DC load.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
The following users thanked this post: Avacee

Offline mcinque

  • Supporter
  • ****
  • Posts: 999
  • Country: it
  • I know one thing: that I know nothing
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #36 on: September 19, 2017, 06:24:37 am »
ok we can argue if they can improve or not, that's right. Interface, software, etc. Everyone can improve.
But I ask myself what we're discussing here if they repeated almost the SAME lr heatsink noob mistake they had YEARS ago with the dp832?! :palm:
I can't believe it. Really. It's ridiculous.
I'm basically still a rookie and because of this, even with the best intentions, I often say bullshits
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9510
  • Country: 00
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #37 on: September 19, 2017, 06:42:59 am »
Hi Fungus
How can a MOSFET not be DC specified?
Sorry i'am a Dutch dyslexic monkey, i do my best to make it so understandable as posible  :D
This load is specified for 150V! so the SOA is realy important at these voltages.

That one's rated to 200V so there's a little bit left over.

What voltage would you be happy with? Where do you think a manufacturer should draw the line if they think their customers are going to put more than 150V into 150V devices? 250V? 300V? :-//

In reality I suspect not many people are going to go near 150V on a 200W device. It would be interesting to see if the 'A' version uses different MOSFETs.
 

Offline Jay_Diddy_B

  • Super Contributor
  • ***
  • Posts: 1733
  • Country: ca
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #38 on: September 19, 2017, 07:50:06 am »
Hi group,

Since we are friends, I will share a few pictures of the inside of an HP6060A load. This is a 60V 60A 300W load.

Input Terminals



MOSFETS






I removed the clamp on a pair of the MOSFETs.


There are a total of 8 MOSFETs, four on each side of the tunnel. Each MOSFET is an IRF540. The heatsink is at the same potential as the positive input.


There is one sense resistor and one op-amp controller per MOSFET. You can you can see the sense resistors, but too hard to photograph. The resistors are in the center of the tunnel.

Big Picture



Look at all that thru-hole goodness !!!



Regards,

Jay_Diddy_B
« Last Edit: September 19, 2017, 07:59:23 am by Jay_Diddy_B »
 

Offline thm_w

  • Frequent Contributor
  • **
  • Posts: 968
  • Country: ca
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #39 on: September 19, 2017, 08:22:26 am »
The A-Model has more software (remote-control) features enabled out of the box, a better slew-rate and higher frequency range to use. ;)

Banana-Plugs are not specified for 40 oder 60 Amps. Thats why they are not used in these kind of loads.
But most people won't be using them at full load most of the time. Omission is annoying.

I think there is a valid concern that someone will plug in some banana leads and run 60A through them. They will then proceed to catch fire. Although its probably a simple cost saving measure, as TTI offers an 80A load with some kind of banana terminals: https://www.aimtti.us/product-category/electronic-loads/aim-ld400series

They could definitely sell/include a small adapter PCB though, to convert the huge terminals to standard banana jacks. Would be easy for someone to design one.

Hi group,
Since we are friends, I will share a few pictures of the inside of an HP6060A load. This is a 60V 60A 300W load.

So the HP 60V 60A 300W load is using 100V 28A*8 FETs IRF450.
Rigol is 150V 40A 200W load using 200V 30A*8(?) FETs IRFP250N.
30% vs 60% voltage margin, but who knows if the 100V choice was intentionally selected or, just the closest voltage spec that happened to exist. Either way the component choice doesn't seem unreasonable in comparison.

Also as someone mentioned in the YT comments, the non-A version does not have color coding. In the case of the DP832/DP832A power supplies its the same, the cheaper one uses monochrome colors only on the LCD and does not have colored buttons. I agree its an odd choice, but that's their way of differentiating the market segments, and its something that is partially "unhackable", unless you want to print a new front sticker.
« Last Edit: September 19, 2017, 09:13:51 am by thm_w »
 

Online nctnico

  • Super Contributor
  • ***
  • Posts: 16712
  • Country: nl
    • NCT Developments
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #40 on: September 19, 2017, 08:34:41 am »
I have used these type of binding posts (rated 200A) for a project. They also accept 4mm banana plugs which is handy but ofcourse you can't have 200A through a banana lead.
« Last Edit: September 19, 2017, 08:38:11 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Smokey

  • Super Contributor
  • ***
  • Posts: 1557
  • Country: us
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #41 on: September 19, 2017, 05:20:49 pm »
What OPP and OCP stand for is buried pretty deep in the manual.

Apparently Rigol engineers are fans of both RoboCop and Naughty By Nature...
You down with electronics loads with OPP?????
 

Offline blackdog

  • Frequent Contributor
  • **
  • Posts: 569
  • Country: nl
  • Please stop pushing bullshit...
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #42 on: September 19, 2017, 05:41:32 pm »
Hi,


Let put the HP 6080 DC load in perspective...

Max. 60V and Max 300-Watt, thats 5-Ampere and it uses 8x IRF540 parts.
5-Ampere trough 8 Mosfets is a little more than 600mA a Mosfet! at 60% of the Vds. (Rigol use 80% of the max. Vds and that is bad for de max. SOA)
The DC SOA spec of the ST brand says about 1.7-Ampere at 60V, looks like HP use a better safety margin :-)
And HP have to keep the IRF540 realy cool, 300-Watts/8 is 37.5 Watt a Mosfet, i think at full load it will sound like a F16  :-DD

There the is a big difference between the ST IRF540 and the IRF IRF540, ST part looks to have a mutch better SOA...
So many different specs from brand to brand, that gives me the creeps in this aplication.

Kind regards,
Blackdog

“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline NANDBlog

  • Super Contributor
  • ***
  • Posts: 4225
  • Country: nl
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #43 on: September 19, 2017, 06:30:05 pm »
So many different specs from brand to brand, that gives me the creeps in this aplication.
Well, just dont design and review DC loads then, because you are obviously not comfortable with it.
I bet you, that Rigol, HP/Agilent/Keysight tested orders of magnitude more number of FETs, under full load for longer time, than the people writing the datasheet. I did for some parts, that's for sure. There are devices, they've been operating for decades, some of them under full load, and you run around, hands in the air, shouting "Its gonna blow any minute! Everyone run! Its not in the datasheet!"
 
The following users thanked this post: Someone, lukier

Offline blackdog

  • Frequent Contributor
  • **
  • Posts: 569
  • Country: nl
  • Please stop pushing bullshit...
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #44 on: September 19, 2017, 07:09:31 pm »
Hi NANDBlog,

Maybe its better that you try to understand wat i try to say...
Like Rigol is using the IRFP250 much closer to there Max. Vds than HP in there 6060A, more change it wil fail.

And i think HP, like a told before, uses a better savety marging and i trust the HP design team more than Rigol.
Take al look at al the big differences for the datasheet for the IRF540 from different brands, these are not the same Mosfet!
So, if you blow the power section witch part are you gonna use? ( of course the HP component for the 6060A  :) )

Design a DC load for yourself, no problemo, if yo want to do production for 3000 units, are you gonna use a Fairchild part?  or ON semi (if these still exist)
Can i replace it with a IRF part (Vishay) or ST, wat about the internal capacitors in de Mosfet, every brand it is different. (maybe thats the source of the instability of the Rigol  :) )
Do i have to use more compensation so that i can use all brands IRF250, do i still reach my power bandwith...

Yes! these IRF250 Mosfets are cheap, but can also be problematic to use, effery brand tells you to read an respect the datasheet data.
There are to many electronic designers wo are not enough aware of SOA problems, or thermal problems like the linear regulators in the Rigol products.
Or are pushed by the braindead marketing department, to make stupid decisions. (Rigol buttons, text, linear regulators, wiring in my Rigol DP832A Power Supply, 470uF! over the output for a 3A Power supply, van noise, etc.)

I like to test a Rigol DC load fo a day on 160V full load at 40C room temperature, lets see what happen...

Kind regards,
Blackdog

“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline lukier

  • Supporter
  • ****
  • Posts: 591
  • Country: gb
    • Homepage
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #45 on: September 19, 2017, 07:23:45 pm »
I too think that the SOA argument is making mount of a molehill.

All cheap (BK,ITech,Maynuo etc) DC loads use IRF540. Agilent as well, also in N3302A (see service manual). It's fine as long as it is characterized and tested.

What I find "interesting" with the Rigol DL3021 load is the amount of computing power there. iMX for the comms and UI - OK, but why CPLD for the front panel and big FPGA, just to read ADC samples or set the DAC.

Also, maybe I missed that from Dave's video. Where is the isolation between the iMX/UI and the FPGA/ADC/DAC? Is this load mains earth referenced? That would be rather odd.
 

Offline NANDBlog

  • Super Contributor
  • ***
  • Posts: 4225
  • Country: nl
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #46 on: September 19, 2017, 09:55:08 pm »
if yo want to do production for 3000 units, are you gonna use a
I made larger productions than that, with FETs with absolutely no DC rating. Yes, in DC mode. You are in write only mode.
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 9510
  • Country: 00
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #47 on: September 19, 2017, 10:38:23 pm »
Hi NANDBlog,

Maybe its better that you try to understand wat i try to say...
Like Rigol is using the IRFP250 much closer to there Max. Vds than HP

It's within the manufacturer's specification.  :-//

(by 25% - quite a large margin, really)

This load probably won't be used at 150V very often simply because it doesn't have enough Watts for people who usually work with 150V.

(I suspect most people who use this load will be more interested in amps than volts)

 

Offline blackdog

  • Frequent Contributor
  • **
  • Posts: 569
  • Country: nl
  • Please stop pushing bullshit...
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #48 on: September 19, 2017, 10:50:46 pm »
Hi  NANDBlog,  :)

You are in write only mode
Oooo, please give me the spec's of what you build, and how it is used fo years...
I have no problems with a IRF540 on relative low DC voltages and high power.

If you look at the datasheets, if there is a DC spec, its at 25C case temperature, that wil be a hell of a heatsink.
And yes, i will give you that the IRF540 is better than most of the modern parts voor DC. :-)

Dit you read my reply #24 about the IXAN0061 application note?

Kind regards,
Blackdog
 
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline blackdog

  • Frequent Contributor
  • **
  • Posts: 569
  • Country: nl
  • Please stop pushing bullshit...
Re: EEVblog #1023 - Rigol DL3021 Electronic Load Teardown
« Reply #49 on: September 19, 2017, 10:59:52 pm »
Hi Fungus,

I have no problems is te Rigol is testing a 24V battery at a high current, but its spect at 150V.
The SOA becoms more an more a problem, in the higer part of the Vds.
Somone already told here, that older parts are better than the modern switching Mosfets, just be careful...

Read the IXAN0061 application note and some other SOA problems with Mosfets, use google to find the info.

Kind regards,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf