EEVblog #314 - Korad KA3005P PSU Teardown - Page 1
Forum section: electronics / general

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 17, 2012, 06:38:39 pm
content: Interesting to see that it has 5 memory leds but only 4 memory buttons, guess they make more than 1 model

author: firewalker
author_rank: Super Contributor
timestamp: July 17, 2012, 07:24:55 pm
content: WTF... They scraped out the infos of a chip that has a unique id? Idiots, just an "lsusb -vvv" will reveal everything.Alexander.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 17, 2012, 08:12:45 pm
content: I must say I dislike several of the things Dave managed to like about that thing. The earth wiring all over the place, instead of all connected properly to one central pointThe cooling directly at the fan, so the near-field fan turbulences can generate the maximum amount of noise when sough at the heat sink bordersThe opto isolators, well, where are the cutouts below them?The tinning to increase the current capacity. Well, that never works well, cf. the resistance of copper vs. solder and you get an idea where the current flows. The hot glue right in the area where the PSU gets the most warm, and the hot glue gets the most soft again.The big cutout above the DB-9 and USB is likely not for a DB-25, but a GPIB interface. Ok, as if anyone would waste money on enhancing that PoS with a GPIB interface.The solder bridges and missing resistors in the DAC area could be the manufacturer's idea of a coarse calibration, the rest then done in software.The metal plate could be to direct a little bit of air flow over the transformer.

author: Rufus
author_rank: Super Contributor
timestamp: July 17, 2012, 08:13:47 pm
content: The plate in the middle is to guide airflow from the vents in the side past the transformer.The choke and capacitor bodged onto the USB board supply along with the earth strap look like fixes for EMC problems

author: veryevil
author_rank: Unknown
timestamp: July 17, 2012, 10:05:58 pm
content: Hey, would love a DaveCAD diagram of that '595 resistor network DAC. Seems interesting? What sort of accuracy / resolution could you get with that?

author: markus_b
author_rank: Regular Contributor
timestamp: July 17, 2012, 10:07:20 pm
content: At least it is not expensive ($99 on Amazon).Dave, can you perform some basic measurements ?Are the USB and serial ports insulated from the power output ?

author: KTP
author_rank: Frequent Contributor
timestamp: July 17, 2012, 10:13:47 pm
content: @BoredCome now, a little harsh weren't we? I am sure the power supply is perfectly acceptable holding a door open or some such suitable application. The heavy transformer almost guarantees it will work for that.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 17, 2012, 10:16:10 pm
content: Quote from: Bored@Work on July 17, 2012, 08:12:45 pmI thought about a similar thing... Although I can't see the heat sink in detail, it seems to me it is just a thick plate with those thick but very short fins on the side, thus the fan seems to be blowing directly to a slab of aluminum instead of creating the proper airflow through longer fins..But oh well... Maybe Korad's procurement department found out that a "real" heatsink would be more expensive than the fan/aluminum combination they chose...I also think that scraping the device markings in the 21st century is really childish...

author: Ketturi
author_rank: Regular Contributor
timestamp: July 17, 2012, 11:46:33 pm
content: What is that white residue on PCBs, nearly every low-cost electronics have it. It's not the best designing, but if it works then no complaining about(my own diy linear "lab" PSU's are much worse, but heck they still work well).Why so often there is design flaws etc. in cheap electronics. It's possible to engineer things cheaply with inexpensive components but bad design and poor parts together is dead last thing to do. And still it happens so often because consumers insists cheap and good, both rule out another, and cheap usually wins.Resistor network, the old way to do D/A conversion, even some soundcards used that practice. Those good old times. I wonder how many bits that DAC correspond. One option could have been to use some micro with integrated DAC. But in this application there is no need to high precision or pcb space saving so probably they figured out it is most cost efficient way.Microcontroller in PSU might be some generic cheap one, maybe even AVR. It could be reverse-engineerable comparing usual micros pinouts in that package to PSU's one. If manufacturer is stupid they might be even left flash/spi/whatever programing interface open but blah who cares. Pretty pointless to copy cheap design to even cheaper device :-D

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 17, 2012, 11:50:32 pm
content: I didn't like how close the current sense resistor was to the wiring from the mains switch.And that DAC is ridiculous - PWM would be simpler and more accurate.

author: gxti
author_rank: Frequent Contributor
timestamp: July 18, 2012, 01:20:59 am
content: 14:10 - Those look like JST VH connectors (or a clone thereof), rated for 10A.How did I miss this when I was searching for my first bench supply? I ended up getting a $90 20V/3A unit from Mastech with a much poorer (although still acceptable) build quality, passive cooling only and it definitely can't sustain 3 amps at any voltage for more than a minute. I did a test run with a thermocouple and had to cut the power at 125C on the transistor case. Would have readily ponied up for something with memory and decent cooling! Still a decent unit, but now I'm looking for a switching supply for my second.

author: DarkPrince
author_rank: Regular Contributor
timestamp: July 18, 2012, 01:35:35 am
content: I assume this is just another clone of the well known units. Question is, are there artifacts on the outputs (during power up/power down)? Granted nothing should be hooked up during the start-up anyways... I know i'd forget one of these times. POP.

author: free_electron
author_rank: Super Contributor
timestamp: July 18, 2012, 01:38:52 am
content: what is this obsession with underrated heatsinks with humongous fans on them .... its a piece of stupid stamped aluminum with a crappy fan.if you buy an equivalent range supply ( max volt and max amp ) of a 'name;' brand the transformer is double the size and the heatsinkg 5 times larger ...shave a nickle and dime... for 99$ no thanks.i got an old analog tenmayears ago (2001) for 99$. that has a big honking transformer ,digital readouts and everything.they spent more money making a cusomt rubber keyboard and controller pcb than the entire transformer rectifier cap pass transistor combined.FAIL

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: July 18, 2012, 03:25:03 am
content: Dave, I think you were a bit too forgiving in this review.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: July 18, 2012, 03:34:05 am
content: I laughed a little when I saw the resistor network because I knew what it had to be. That appears to be a total of 24 bits, although they may be distributed between different things, say 16 bit voltage control and 8 bit current control. (There are three TL082's right to the right of the resistor network, so it's plausible.)I can imagine that some people these days would give away 74hc logic for free in large quantities, or even pay you to dispose of a ton of it. I can see how a bunch of 595's and resistors would be cheaper than a "real" DAC or a microcontroller with enough PWM precision and channels, but good enough. And since it's going to generate a DC voltage most of the time, you can get away without the filtering needed for a PWM ( = less precious engineering time).Also agree with Mike that the shunt is too close to the mains wire. One of the things I spontaneously reacted to.

author: free_electron
author_rank: Super Contributor
timestamp: July 18, 2012, 04:49:08 am
content: Just watched the whole video. Looks like that metal plate above transformer is to force the airflow down over the transformer before it goes out throught the side vents. That transformer is probably 'critically dimensioned' ( read: it runs hot .... )The resistors look like they are marked 1002 and 2002 10k and 20k that would fit a classical R-2R style dac. They probably read the voltage and current using a sar algorithm...This is most likely cheaper than something like a dual i2c adc and dac .. As they can use the dac as adc .. And they can get away with a larger output voltage.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 18, 2012, 05:10:43 am
content: Maybe the MCU has an ADC and they use that for measurement, and the DIY DAC for setting. Or they skip the measurement (analog control loop), and the front panel just has a conventional ammeter and voltmeter.Some more speculation. Maybe they need the external memory to hold "calibration" data for the "high precision" DAC.

author: Scopeman1
author_rank: Contributor
timestamp: July 18, 2012, 08:15:41 am
content: Dave, I reckon the piece of aluminum in the center that you did not know its function is to divert the air flow when the case is on. It will send it down past the txfmr to the power board.

author: Scopeman1
author_rank: Contributor
timestamp: July 18, 2012, 08:24:36 am
content: I think the fixed transformer voltage stops us from bringing in the USA versions on Amazon. Mind you I don't mind paying a bit extra for a local supplier with local warranty. I see Trio Smartcal has it at $199 AUD. Fair I suppose but would not want to pay more. The return freight for a warranty repair to the USA would be more than it's worth!!

author: tramjoe
author_rank: Regular Contributor
timestamp: July 18, 2012, 09:44:50 am
content: What a coincidence. I was exploring a (very) similarly spec'ed PS just last night, and my findings left me wondering about distributors margins and, as for many chinese lab hardware, the inevitable rebadging / copying dance that goes on there.Look atthat(in french, but you'll get the idea, and google translate is your friend). €300 ! Just for fun, I contacted the maker's Alibaba's distributor and his first price before even any bargaining (though in volume for 30 pcs) was lower than $100, that's about €100 after taxes and shipping to France :-) 200% markup aka 66% margin, life is good for electronics distributors in France :-) No wonder why they offered me a 30% rebate on this unit to compensate for a slight hotline problem I had with them. But even at that price (€210), it does seem a lot too similar to that Korad to be a good deal ;-) I guess the Korad is the ripoff/rebadge and the MCP the original one, because the MCP does have the 5 function keys, and looks a bit better constructed or at least european-market-conscious with IEC1010 protected plugs and a bit nicer front panel.What do you think guys ? Looks really _closely_ spec'ed, however the MCP unit is totally non-existent on the internet, apart from that french distributor and alibaba wholesale distributors, at least under that name and ref # :-)Interestingly, MCP also makes 1A and 3A versions of the same unit, and a surprising 300V/400mA version of it.Oh, and BTW everyone is quoting Dave's $99 amazon deal on the Korad, but there is actually a "D" version there which is non-programmable but has 110/220v input for $10 less, and I could swear I saw a couple of hours ago the P version for $75 with another amazon vendor with only 2 units left.... even showed it to my wife :-D

author: amyk
author_rank: Super Contributor
timestamp: July 18, 2012, 10:22:54 am
content: Quote from: Bored@Work on July 18, 2012, 05:10:43 amAfter watching the video I believe the MCU is this, from the location of the crystal and arrangement of the pins:http://www.stc-51.com/datasheet/STC12C5A-english.pdf8051-based, not surprising. I've noticed '51 isverypopular in Chinese electronics.

author: T4P
author_rank: Super Contributor
timestamp: July 18, 2012, 12:23:54 pm
content: Quote from: amyk on July 18, 2012, 10:22:54 amWell yeah, it's tried and tested for them. Not that they will venture much outside of their "safe" zoneThe "weird" and rare ones they use are ST's STM32F103

author: poorchava
author_rank: Super Contributor
timestamp: July 19, 2012, 10:42:02 am
content: Ya know, I'm seriously thinking about buying one (or two) of those (half-year bonus sallary coming |^^|). Turns out we have an authorized reseller in Poland offering most of the single channel solutions from Korad (on their website even 3-channel versions can be found).KA3005P is priced at 335PLN (=99 USDB at current stock exchange rates) while KA3003P is at 325PLN (=96USD). I wonder what's the actual difference in hardware between those two. Obviously can't be too big if they are almost at the same price.Maybe that's some kind of Rigol-bandwidth-method? Like different firmware or some jumpers on the pcb limiting the current?

author: EEVblog
author_rank: Unknown
timestamp: July 19, 2012, 11:58:50 am
content: Quote from: poorchava on July 19, 2012, 10:42:02 amI have been told that the 5A one has a bigger transformer, but that's the only difference.Dave.

author: poorchava
author_rank: Super Contributor
timestamp: July 19, 2012, 02:16:54 pm
content: Huh, that kind of explains such small difference in price. Of course software has to be different to go up to 5A with current setting. I'm wondering what kind of pass transistors did they use. I mean a pair of old-school 2N3055 bjt's could easily do it (plus they are very cheap and being manufactured by a dozen companies or so)

author: T4P
author_rank: Super Contributor
timestamp: July 19, 2012, 03:19:29 pm
content: Quote from: poorchava on July 19, 2012, 02:16:54 pmWe're in 2012, think ahead.

author: PChi
author_rank: Frequent Contributor
timestamp: July 19, 2012, 04:26:39 pm
content: I don't think that 2 2N3055 pass transistors are adequate. Looking at the Multicomp 2N3055 data sheet for the Active Region Safe Operating Area when the Collector Emitter Voltage = 50 V the DC maximum collector current = about 1.5 A so it's in the secondary breakdown region.So if the control software gets confused and the Power Supply attempts to output 5 A into a short circuit with the transformer tap set to maximum the power transistors are at risk which is I guess why they quit.It's also wise to use a branded part. Not all 2N3055 transistors are created equal and some may not even meet the data sheet specifications.Just like another poster I was disappointed not to see smoke.

author: ee851
author_rank: Regular Contributor
timestamp: July 19, 2012, 08:16:42 pm
content: Dave, did you test this PSU? How well does it work? Does it protect your load circuit from over-voltage ? over-current ? without smoking ?

author: McMonster
author_rank: Frequent Contributor
timestamp: July 20, 2012, 12:56:09 pm
content: Quote from: PChi on July 19, 2012, 04:26:39 pmI have a different cheapish PSU, analog Atten APS3005S, that's also rated at 30 V, 5 A and it in fact uses two 2N3055s transistors. It wouldn't surprise me if this Korad PSU also used them, that's what you pay for. Hopefully my Atten PSU will live at least until I get or build some better unit.

author: T4P
author_rank: Super Contributor
timestamp: July 20, 2012, 07:12:55 pm
content: I saw a TO-3P/TO-247 package inside so i can safely assume it might not be the 2N3055speaking of running on the edge anyway, 5Amps at 30V is the basically the limit for the SOA graph of the 2N3055 and that's ... you know, shoddy transistors and such.Man, why won't they use more recent transistor anyway! ( It's hard to find a recent one, since they all mostly gone the way of the dinosaur in terms of new designs, only leaving us with more and more and more mosfets )http://sg.element14.com/on-semiconductor/njw0281g/bipolar-transistor-npn-250v/dp/1640122

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2012, 08:46:42 pm
content: Just bought a PSU today, no need for a teardown as it is a shop soiled unit ( so no return, but no small of smoke so probably quite fixable, I have bought these before) that uses a 2SD717 as pass transistor. Most likely just dead parts, will test tomorrow and see. 13.8V 3A fixed, probably will make a variable out of it.

author: teixeluis
author_rank: Contributor
timestamp: January 16, 2013, 12:08:00 am
content: Hello Dave,My Korad KA3005P PSU I ordered through Amazon have just arrived. At first I stumbled upon a pretty ugly production mistake: the positive and negative power posts had the colours swapped! Apart from that everything ok, at least from an initial inspection. Mine has a switch in the back to toggle between 115V and 230V input. Had to change to 230 V because I live in Europe (the PSU was bought from the american supplier SRA Soldering Products.Anyway I coudn't resist opening the unit to fix this minor issue. Upon opening it I found that it has the new regulator circuit board (supposedly dealing better with heavy loads than the one you tested). The board had one difference however: instead of the large 6800 uF capacitor it has three smaller 2200 uF caps.Another detail of this model, is that instead of the M5 led it has a led labelled as LOCK, and is set when we press the corresponding button (to of course lock the keypad). A very good improvementI haven't done any torture tests yet, only a few basic tests. I notice that the fan reacts quite dinamically to the load changes (supposedly varying the rpm based on the temperature). It vibrates somewhat, even after providing extra torque to the fixation screws.Regarding the PC interface, I could not install the CDC driver in my Windows XP. Apparently the .INF file is not correctly written. I then tried booting in Ubuntu linux, and it was pretty straight forward. After turning on the power supply linux recognizes it as being a generic usb cdc device, creating a device under /dev/ttyACM0. Through minicom I managed to issue the commands described in the manual contained in the cd-rom. It supports SCPI style queries such as *IDN? As the Windows drivers could not be installed, I could not test the program included in the CD-ROM. However, as the commands are documented, it is a pretty straightforward task to write a similar application in Java or even C/C++.I tried to measure the ripple, but could not distinguish it from the 12 mVpp of noise at the probe, even with the PSU turned off completely.Overall, assuming no more issues are present in this version of the PSU, this is a pretty nice buy for the price. Most other products in the same price range aren't nearly as interesting as this one. I would say this is the Rigol DS1052E of the PSU'sAnother interesting fact is that this matches the Velleman equivalent:http://www.velleman.eu/products/view/?country=fr&lang=fr&id=409798which is pretty much the same power supply.Best regards,Luis

author: Bored@Work
author_rank: Super Contributor
timestamp: January 16, 2013, 05:49:19 am
content: Quote from: teixeluis on January 16, 2013, 12:08:00 amSince you have it running on linux you could use lsusb to get the vid/pid of the usb chip they use. Then you google for the chip, go to the chip manufacturer's web site and look for their windows driver and install that driver.

author: teixeluis
author_rank: Contributor
timestamp: January 16, 2013, 02:18:42 pm
content: Quote from: Bored@Work on January 16, 2013, 05:49:19 amIn fact I did that in the very beginning, still under windows (you can fetch the VID and PID from the device tree, in the control panel, even for unknown devices), but could not obtain anything interesting upon googling it. It is some Nuvoton chip with USB functionality. If you have pointers to the correct driver it would be great.Best regards,Luis Teixeira

author: jnd
author_rank: Regular Contributor
timestamp: January 16, 2013, 03:31:41 pm
content: Quote from: teixeluis on January 16, 2013, 12:08:00 amI noticed both the label at the back and voltage switch have only 110/220 V, not even the usual 115/230 and some European countries have even 240 V so it's clearly not made for Europeans. Can you try the maximum output? I don't remember if it's software or hardware limited but it should go a bit over 30 V, without blowing up the transistors.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 16, 2013, 06:38:18 pm
content: Quote from: teixeluis on January 16, 2013, 02:18:42 pmOh dear, some largely unknown company.If you aren't tired of it, I could think of two more things:More investigation on Linux. Using lsmod, dmsg, etc to figure out what driver is loaded and if it happens to be a generic one for several chipsets. This might give you an idea if some windows driver from some other manufacturer might work.Or studying the .inf file of the driver on windows to figure out if it loads a generic driver, which files it wants to install, which registers it tries to set. You could also try to point the windows device manager directly to the .inf file when it asks for a driver.Not really fun.

author: teixeluis
author_rank: Contributor
timestamp: January 16, 2013, 09:34:03 pm
content: Quote from: jnd on January 16, 2013, 03:31:41 pmAnd indeed it has a 110/220 V transformer inside, like shown in the picture. At no load I get a maximum of 30.91 Volts read from my multimeter (a UNI-T UT61E) against the 31 Volts shown in the power supply display. The drift between the two seems to increase with voltage. For instance, at 1.00 Volts on the PSU display, my multimeter reads 1.0072My mains voltage is at about 236 Volts (true rms reading).Best regards,Luis Teixeira

author: teixeluis
author_rank: Contributor
timestamp: January 16, 2013, 09:43:37 pm
content: Btw, a closeup view of the Nuvoton chip in the attached picture. And also a few details of the device recognized by linux:$ lsusbBus 003 Device 003: ID 0416:5011 Winbond Electronics Corp.And the output of the dmesg command:692.809109] cdc_acm 3-2:1.0: ttyACM0: USB ACM device[ 692.816395] usbcore: registered new interface driver cdc_acm[ 692.816400] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters[ 722.096069] usb 3-2: USB disconnect, device number 2[ 724.320048] usb 3-2: new full-speed USB device number 3 using uhci_hcd[ 724.523186] cdc_acm 3-2:1.0: This device cannot do calls on its own. It is not a modem.Nuvoton seem to be a spinoff of Winbond or so.I have tried the same inf file under a virtual machine with Windows XP as well and it worked. It must be some problem in the OS installation.Best regards,Luis Teixeira

author: staze
author_rank: Frequent Contributor
timestamp: April 08, 2013, 07:29:23 am
content: still liking the power supply? looks like it might meet my criteria and then some.

author: Svuppe
author_rank: Regular Contributor
timestamp: November 02, 2013, 03:21:25 pm
content: Has anyone done some more reverse-engineering on this PSU, other than what has already been said here? The reason I ask is that I have this PSU (though in a Vellemann disguise), and it works like crap. Not far from what is seen in EEVblog #315 when it fails. However, mine is the new and "improved" version, and as far as I can tell, the output transistors are NOT blown. It is the controller board that is acting up from time to time.My plan is to throw out that crappy controller board, and replace it with a homemade one instead. I'll be re-using the power stage and the front panel, so if anyone has had a look at the interface between the boards, then I'd like to know about it. Then I could have a little less reverse-engineering to do.-Mikael

author: Svuppe
author_rank: Regular Contributor
timestamp: November 03, 2013, 07:16:37 pm
content: Quote from: Svuppe on November 02, 2013, 03:21:25 pmIt didn't have to come to that after all.I had a good look at many of the signals on the controller board today, and while poking around, I suddenly found the problem. The clock signal to one of the 74HC595 was intermittent. Probably a bad via beneath the chip or something like that. That caused data corruption in the shift registers, making the R2R DACs produce random voltage and current settings. A small piece of wire and two solder blobs later, and everything works perfectly.It would have been fun to make my own controller board replacement though.-Mikael

author: cavlovic
author_rank: Contributor
timestamp: November 04, 2013, 03:57:58 pm
content: Quote from: Svuppe on November 03, 2013, 07:16:37 pmCould you post a few pictures of your board and fault? I seem to be having similar problem with mine:https://www.eevblog.com/forum/testgear/korad-ka3005p-power-supply-calibration/

author: Svuppe
author_rank: Regular Contributor
timestamp: November 04, 2013, 07:32:39 pm
content: Sure, I can do that. Just not tonight though.But there won't be much to see. Just a single wire connecting pin 11 on one 74HC595 to pin 11 on one of the other 595's. The fault is under one of them, so it can't be seen.-Mikael

author: Svuppe
author_rank: Regular Contributor
timestamp: November 05, 2013, 04:11:21 pm
content: As promised, here is a picture of my repair. Only the wire is my doing. The rework with the 330 Ohm resistor was already there.-Mikael

author: anakron
author_rank: Newbie
timestamp: December 15, 2013, 09:19:30 pm
content: Anyone had any luck finding a Windows 7 driver?The PSU I just got has drivers from September 27, 2013 - only for XP.It does not install on Windows 7/x64 and VMware (latest version) does not list it in the removable devices.So ... I can't get contact.Kent

author: anakron
author_rank: Newbie
timestamp: December 15, 2013, 09:44:19 pm
content: SOLUTION:The Velleman supply is indeed the same.http://www.velleman.eu/support/downloads/?code=PS3005D&type=I plugged in the USB and when the install window for the USB came up, I merely pointed to the cdrom directory with "include subdirectories"and the Nuvoton driver was found and installed.Then I installed the Velleman software.The Velleman software as well as the Korad software works perfectly now.The most recent Korad software does not remember the comport it needs to connect to.The software just virtualizes the instrument and shows a fast graph of the power.The Velleman software does the same, but has no pretty buttons. It has one positive side - it autodetects the comport.But do I want that? I wonder what it does to the other comports in the process.Kent