EEVblog #511 - Rigol DP832 Power Supply Teardown

[rs20]

So one thing that I noticed in the episode is that the current sense resistors appear to be on the negative rails. So I did a few tests, which I've got here in both video and text form (take your pick):



Text: So I did some tests and:
A. There's a 40 milliohm resistance if you pass current into Ch2– and out of Ch3– (which are, in theory, common/supposedly shorted out), which corresponds exactly to the theory that current has to pass through both 20 milliohm resistors to get from one to the other.
B. However, if you short-circuit Channel 3 and test for a voltage drop across Ch2–/Ch3–, it fails to materialise. If there was a 20 m? resistor between Ch3– and """true ground""" , then you'd expect to be """true ground""", and therefore Ch2–, to be 60mV lower than Ch3– at 3A. Instead, it's 0mV different.
C. Ch2– and Ch3– appear to be identical; it doesn't matter where you sink current that is sourced by Ch2+ or Ch3+, the current measurement is always spot on. So what are those resistors doing!?

I'm tearing my hair out, I can't figure out a circuit schematic that exhibits this combination of behaviours. Probably missing something obvious though!

[fridrik]

Isn't the regulation just handled on the low side on both channels, that means that the negative terminals on both channels are circuit ground. Then on each channel you would have the current sense resistor and mosfet in series with circuit gnd connected to the input circuitry (triac prereg). That however does not explain the 37 mOhm resistance you measure between the negative terminals, is it possible that it can be accounted for by just the leads internal to the supply, and the ~40mOhm is just a coincidence?

[unnecessarynitpicker]

It looks like the two sense wires are joined together in the connector in the right of the picture, but the other two supply wires do seem to go through those  20 milliohm resistors before going ?.

The grey and black wires seem to be coming from the two common terminals..

[GiskardReventlov]

Just getting around to watching past episodes.  I didn't see the siglent video but I thought it was funny to hear "yeah there's rust on this but not as bad as siglent's".  New lab equipment that has rust is really cheezy.  Who wants to buy a brand new car that's already rusting?

Lack of attention to detail in one area makes one wonder where else they've cut corners. I'm glad you mentioned it though because I'm sure they're watching.

The display is too small for me, they should have an option so that you can make one channel consume all the screen area. (maybe there is and I missed it?)  They could also just have a bigger screen by moving the channel buttons down (as Dave suggested).  Does anyone know if they've resolved all the issues that were discovered?

[mcinque]

I didn't see the siglent video but I thought it was funny to hear "yeah there's rust on this but not as bad as siglent's"

could you please link the video at the minute when Dave said it?

[GiskardReventlov]

could you please link the video at the minute when Dave said it?

It's in the teardown video, don't remember where.

[giubin]

What's the point, Citizen. You carefully put this comment both on the blog andd youtube comments.
For a few video's already.
The obligatory Citizen rant.
Blogger envy?

It seems all he does is complain, so I'll no longer respond to his comments directly.
Of course, he conveniently forgets the fact that my previous teardown video (the UPS) combined whiteboard stuff with the teardown which made it quite popular. But no, that doesn't fit with his opinion that my teardowns are just the same and useless, so he ignores those ones.
This one was obviously for those who wanted to see inside the Rigol supply, and nothing more. I never claimed it be anything more.

Thanks for your videos. You work hard and help us a lot. You help me choosing the right stuff and I learn always something. I like this Power supply.