Teardown: Agilent E3631A Power Supply (Picture Heavy)

[free_electron]

You obviously have a very strong conviction that this can't be done.

what i'm saying is that you can't design an identical supply at that price. Identical in terms of electrical specs, performance , io and communication.

The linear section of these supplies os nothing special. I guess you can replicate that for 10$ without mechanics or transformer. After all its only two opamps, a current source and a fat transistor.
Slap on a dual channel 16 bit dac to set cvoltage and current, under control of a cpu over an optical rs232 link. I would look at analog devices aduc8xx series cpus. Cheap and they have abuilt in 24 bit A/d ... You can drive a local lcd display and rotary encoder. Display voltage and current. Push encoder to toggle between current and voltage. The moment you turn , the set values are displayed. One second after last turn it switches to real values. Use one extra button for channel pn / off.

Three optos doe the work two for rs232 one for global on/ off.
The chasssi processor needs two uarts or one uart and ethernet.
Chassis processor controls global on/ off and powerup sequencing and does interfacing.
You can use the intel 9 bit uart mechanism where the ninth bit signifies address/ command.
Very easy to make a distrbuted system that way

[gerrysweeney]

@free_electorn - I agree as a one off thats not possible, but that was never what I was trying to do. I  would say though, that if one had enough conviction it could be done, you could compete with HP, you just need to design something well (like they have), do some reasonable volume (like they do), make it in china (like they do) - after all, Agilent would appear to be able to do it and make a margin doing it - or perhaps they can't; that could go some way towards explaining why HP are in a financial hole

I will have a look at the aduc8xx series chips, I was not aware of them.  That said, I know PIC's well and have all the tools, code libraries etc so that should be much faster for me to get up and running and debug - they don;t have a 24-bit A2D built in though, but as I said, I do like the idea of creating a dual or multi-slope ADC just to learn more about the approach.   Keep an eye on my blog for progress, you won't find the first few parts of much interest, its just me coming up with my own variation of a CV/CC controlled regulator circuit as I get more familiar with the nuances of regulator design.

Thanks for the posts, certainly food for thought and an excellent source of motivation

Gerry

[free_electron]

@free_electorn - I agree as a one off thats not possible, but that was never what I was trying to do.

even in moderate volume it will be hard.. You'r ebritish. Thurlby Thandard ring a bell ? They make good power supplies. I got multipleof their QM series ( three channels gpib programable. I also have xantrexes ( which are TTI designs , not real xantrex / sorensen )  shitload of electronics inside...

Afaik the agilent supplies do not come form china but from their penang - malaysia plant. Agilent has had an assembly plant in malaysia since the 70's.

i would not try tocome up with my own regiulator circuit. anything that can be done has been done on the linear front.... the best and easiest regulator is a twin opamp where the current monitor pulls down the output of the voltage opamp to provide the foldback. bulletprrof , rock solid ,simple.
if you need some speed in this : drive the base of the powertransisotr using a current source.
Go get the manual of the hp supply and study the 6 volts section... it's hard to make it better than that. it is simplified to the extreme and has stellar impulse response and load regulation. use tht as the basis of your design and scale it up in voltage.

other similar designs are the e3610 series. that regulator method ha been around since the late 70's and it is still being used any almost any supply out there. simply because it is hard toimprove on it.

you could throw in a preregulator using two thyristors in a bridge to bring down internal dissipation. agilent uses that in the e344x series i believe.
other machiens to study : 6624 quad channel machines... the regulator there is very clever ...

[gerrysweeney]

@free_electron - yes I heard of TT, they always reminded me of low-end professional gear, I am sure they have gotten better of late although, but being a british company they are probably not at the bleeding edge of the design spectrum - us brits don't seem to do engineering/manufacturing as well as the rest of the world.

In terms of the regulator circuit, you are absolutely right, I am not trying to invent anything new, but part of this exercise for me is learning what I can about how these well proven designs actually work, what problems they have and how you solve them; you can get a sense of whats right or wrong by looking at other working designs but for me at least, I only truly understand once I have experienced the problems and solved them myself.  What you describe is pretty much what I have ended up with, a pass device, a couple of op amps and a pre-regulator switching device.  I am a couple of steps ahead of what I have published in my blog so far. 

I spent a fair amount of time pouring over the 6v regulator circuit on the 3136A when I was repairing my own, the regulator its self is fairly simple as you say apart form one thing - the use of multiple bias supplies floating around the main regulator supply - a mains transformer to get all those windings would be a custom job and expensive, I might be misguided but I think I can design that need out which in turn makes things simpler.

I am using a FET as a switch for the pre-regulator, simpler and keeps the BOM down (as I use the same FET type as the pass device too), I have not yet put in the analog feedback loop for the pre-regulator, so the controller currently drives it (and yes I know it won't be fast enough and I will be changing it

I did have a constant current source in the driver stage but removed it again, I need to do measurements although just from playing around I think it might be fast enough already, but as I say I can't confirm that.

I will take a look at the other designs you mention although by and large I am there with a working regulator thats good for 50 watts and can be configured for various ranges 0-6/5A, 0-30/1A and some inbetween.  I am using single supply op amps and I think this is why I have a 2mv offset problem which I have yet to tackle.  So nothing new, but I have been through the pain of making it work, getting it stable and understanding the regulator circuit behaviour - big step for me and my own knowledge.  I have also tried to keep the BOM down from the off, so simplicity where possible...

Cheers,

Gerry

[T4P]

Actually if they were made in china it would only last 2 years no?
But they are made in malaysia because the stuff they make in malaysia is pretty good (hakko made the 936 currently makes the triple-8 there as with all others)


Or you can also buy a 120W switching supply from aliexpress and have a postregulator to filter out the noise and also another 24W switching supply as the 5V supply line

As for the post regulator you probably know where i got the idea from ... DJ !

[gerrysweeney]

@DaveXRQ @free_electron - My mistake, I knew they were made in the far east, now I know specifically they are made in malaysia - thanks for the correction.

@DaveXRQ - I have seen the switch mode/post regulator approach before, its a nice idea. If I had anything like the knowledge needed to build a reliable switch mode I would probably give it a go, but alas.....

Gerry

[ben_r_]

Very glad I found this thread! There is some crazy good info in here! I just picked up a used E3631A for $450 and am awaiting delivery. FWIW I called Agilent and found out they charge $146 for a one-off calibration. I might do it seeing as how the one I bought hasnt been calibrated in almost ten years, but I havent decided yet. We'll see when it comes and after I do a bit of measuring of my own.

[boris.t]

Hello.
I have problem. My 3631 say me 550 error for MEAS:VOLT? and MEAS:CURR? over GPIB.
Error 550: "Command not allowed in local. You should always execute the SYSTem:REMote command before sending other commands over the RS-232 interface."
But STST:REM not allowed for GPIB communication.
I have no idea how, but it does not work. Hope to heal it.
Where I can find firmware files?
Sorry. It is Keysight IO Libraries problem, solved by installing previous version.