EEVblog #314 - Korad KA3005P PSU Teardown

[T4P]

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)

We're in 2012, think ahead.

[PChi]

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.

[ee851]

Dave, did you test this PSU?    How well does it work?   Does it protect your load circuit from over-voltage ?    over-current ?    without  smoking ?

[McMonster]

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.

I 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.

[T4P]

I saw a TO-3P/TO-247 package inside so i can safely assume it might not be the 2N3055

speaking 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

[SeanB]

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.

[teixeluis]

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 improvement

I 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's

Another interesting fact is that this matches the Velleman equivalent:

http://www.velleman.eu/products/view/?country=fr&lang=fr&id=409798

which is pretty much the same power supply.

Best regards,

Luis

[Bored@Work]

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.

Since 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.

[teixeluis]

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.

Since 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.

In 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

[jnd]

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.

I 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.

[Bored@Work]

[
In 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.

Oh 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.

[teixeluis]

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.

I 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.

And 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 1.0072

My mains voltage is at about 236 Volts (true rms reading).

Best regards,

Luis Teixeira

[teixeluis]

Btw, a closeup view of the Nuvoton chip in the attached picture. And also a few details of the device recognized by linux:


$ lsusb
Bus 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

[staze]

still liking the power supply? looks like it might meet my criteria and then some.

[Svuppe]

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

[Svuppe]

My plan is to throw out that crappy controller board, and replace it with a homemade one instead.

It 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

[cavlovic]

My plan is to throw out that crappy controller board, and replace it with a homemade one instead.

It 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

Could 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/

[Svuppe]

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

[Svuppe]

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

[anakron]

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

[anakron]

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