Author Topic: Teardown: Agilent E3631A Power Supply (Picture Heavy)  (Read 34556 times)

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Offline vl400

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Teardown: Agilent E3631A Power Supply (Picture Heavy)
« on: October 20, 2011, 02:13:52 pm »
I have had this supply for awhile now and always planned on doing a teardown when replacing the front connectors but still have not got around to it :( Had a chance today to pull it apart and take some photos along with some performance screen caps.

This is a triple output (0 - 6V @ 5A, 0 - 25V and -25 - 0V @ 1A) supply with some fairly reasonable accuracy, noise and ripple specs.











The top board contains the processor, front panel control and +-25V section.











Processor







While the bottom board does the 6V section, HPIB and serial











Front panel board is fairly basic as the processor does the work, so didnt pull it apart any further. Each terminal has its own sense wire. The mounting is nice with tab towards the middle/left that clips it in





And it has a proper power switch  :P






And a few quick tests

No load output on @ 6V


1R Load on 6V


No load output @ 25V


1R load on 25V


10R load on 25V


Weird delayed start that happened every so often







« Last Edit: October 20, 2011, 06:51:08 pm by vl400 »
 

Offline Kibi

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #1 on: October 20, 2011, 07:44:22 pm »
Nice teardown. Thanks for sharing.
Those meters are pretty much spot on! :)
 

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #2 on: October 20, 2011, 07:59:18 pm »
I don't like at all how they have blocked the pressure vents of the capacitors.

Offline Ronnie

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #3 on: October 20, 2011, 11:23:45 pm »
Agilent really makes quality products.
Very clear scope screen shots!   8)
 

Offline vl400

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #4 on: October 22, 2011, 11:58:31 am »
Yeah other than the cap vents being blocked I thought it was well made and thought out. Its not be cal'd since new in the early 2000's  :-[
 

Offline gerrysweeney

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #5 on: May 29, 2012, 06:16:28 pm »
I recently done a teardown and repair of one of these power supplies - I just found this post so I thought I would share my efforts too, text and picture heavy.   

http://gerrysweeney.com/agileent-e3631a-power-supply-teardown-repair/

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #6 on: May 30, 2012, 12:02:39 am »
-edit- one of these days i'm going to invent a non-dyslectic keyboard... ( or learn better typing ). polishing right now ..

A bit more information on this power supply, its design and the how and why, of agilent ( this was designed when they were still hp ) doing the things they did in this design.

First off : those caps do not have their vents blocked. It is silicone isolation to prevent possible shorting of the bare top metal of these caps to the heatsink of the 6 volts section underneath when the lid is closed. Not all supplies have this. Originally there were capacitors that were shorter, only later models use longer caps so they solved it that way. Nevermind , was thinking of another supply in the same series.
Here it is purely mechanical stability.

Second. The A/D is indeed built with discrete components and .. an asic. They use a conversion technique called multislope III which is a charge balancing convertor. It is similar to a dual slope convertor. They charge a capacitor in an integrator circuit during a fixed amount of time from a reference voltage. They then use the, to be measured voltage, to discharge back to zero and measure time again. The ratio gives you the weighted ratio of Vin versus Vref.

The problem with this is that conversion time changes with input voltage. So, what does multislope do? If they detect that they are 'far off' they 'add' or 'substract' reference current. So they can speed up the discharge of the cap. An algorithm switches reference currents around coming from a -10 volt and +10 volts reference through 30 k resistors. They use a simple 4051 to do the switching. A high precision opamp for the integrator and a really good comparator for zero detection.

The asic controls the current switches and holds the counters to measure the times.
So , the whole a/d system does not work with 'volts' but with 'time'. Time that is derived from a charge current derived from a voltage reference.

The beauty of this converter is that all errors are self canceling. Only the precision of the reference is important. If you want more digits out of the convertor .. simply measure time more accurately... This done by increasing clockspeed and having counters with more bits. The absolute clockspeed doesnt even matter as it is a ratio between two numbers. If you get more leading numbers before division you get more effective numers post division.

Now, the machines were designed at the same time als the 34401 multimeter and 34970 switch ... Which uses the same A/D technology and the same asic. So for them , this was a freebie ... And if that display tells you 5.784 volts: that last digit is spot on because internally there is one more full digit ... They have 5 1/2 digits in this design...

You can't really measure anything in this a/d convertor when it comes to troubleshooting ( i've seen 3631's with a bad convertors .. Typically the integrator chip that is fried, not a cheap opamp, its like 8$...) because everything is current controlled. So poking around with a scope probe or voltmeter tells you nothing. The multislope system mechanism keeps all voltage in the convertor at 0 by injecting or extracting currents. so the only thing you see is 'ground' everywhere and you think it's broken. Nope. working perfectly fine. If you don't see '0 volts' somewhere : that's the problem spot.

The A/D does not scan the parameters. It only measures the channel that is beeing displayed on the screen, or temporarily switches over if a request is made through gpib.  The power supply control loops are fully analog.

Core processor is an 80196 with external memory and sram. Again, same beast as in the other machines from that era 33120 generator, 34401 meter , 34970 switch,  basically any machine with vfd's, so they have tons of experience with this thing. Proven design , and for them , very short design cycle as it is paste and repeat ... With some software changes.

Now, the dac is another interesting beastie ...
They use a 16 bit dac to do the setting of all voltages and currents. The dac has a multiplexer on the output followed by analog memories built around tl074 and capacitors . They continously replenisch the caps by scanning and reprogramming the dac. Why not 6 of these DAC's? Because when these supplies were designed one dac costed more than making 6 analog memories with caps and opamps as unity gain followers...

Right. More interesting tidbits.
The cpu and a/d system share a common 'ground' with the +/- 20 output. The 6 volt ground is fully isolated from chassis ground, as is the 20 volt section. Only the gpib and serial port sits at chassis ground. The supplies float in respect to chassis ground, and each other.
So , how do we get the info in and out ? Like i said the DAC is expensive and we already have a superduper a/d... We are not going to replicate that and send it across a digital optical link... That would be too expensive... But wait ! We are HP ! And we make optocouplers... Even analog ones ! Lets do that !

The analog coupler uses an led and two matched photodiodes. Two simple opamps make a system that drives the led , measures emission using one of the photodiodes and makes a servo system. The other photodiode is a mirror... Simply amplify it and done ! Cheap, elegant and very very clever !

Now ,the communication bit.. We find the classical TMS9914 ieee488 controller driven by an 8051 as well as standard rs232 port. These talk through regular digital optocouplers with the 80188.

The front panel has its own 8051 as well. That thing scans keyboard, rotary encoder and the VFD (through high voltage buffers) and talks serially with the 80196 via the asic that ontains a second uart... )

This may all seem like overkill but it isnt... There is again something clever going on.
The VFD requires an ac voltage to drive the filament and a relatively high dc voltage to drive the segments. Problem is that this requires some voltage shifting . The scanning, and high voltage switching, also creates electrical noise. If you blink a digits intensity you see the noise spectrum change. The display is scanned in a matrix.. So this would overload the 80188  , especially when gpib commands would come in you would see a noticable flashing of the display. We are HP.. We can't have that.

So , we give the frontpanel its own processor to keep the scanning noise away from the a/d , offload the main cpu and... Wait for it ... We can do some trickery with the power supplies for the VFD ! The whole frontpanel runs at -18 volts in respect to the ground of the processor. We simply use 4 opamps to level shift the control signals between domains. This negative voltage allows us trickery with the display filament so we only need one additional winding on the mains transformer, which alread has a lot of windings..  4 opamps is cheaper than an extra winding !

So this may all look like it is 'overengineered' but in reality it is not. For them it was very cheap and they actually cut costs. The asic they had, the display system too, the analog optos too . They worked really hard to make this as cost efficient as possible.

Now the supplies themselves. These are fully analog control loops , because even HP would not dare attempt a digital control loop as they know that is always too slow.
The control is very simple. Two opamps do the work. One works as overcurrent detector and can pull the output of the voltage servo downwards. I don't recall of the top of my head the schematic but i believe they use two simple diodes to do that, sort of an analog 'and'

The driving of the power stage is a bit odd too. The make a constant current source with an lm317 and inject this in the base of the power transistor. All the regulation opamps do is deviate this current.
This allows the supply to react very fast , as opposed of having a weak opamp try to drive a relatively large 'load' and be slow at it. And you do NOT want an additional gainstage behind the opamp as this makes the loop unstable. So .. current source it is !

There is a couple of other tricks in that system. They employ a pair of LM339 or LM393 comparators to monitor the delta between iset/ireal and vset/vreal.  Depending on the logic combination they can detect cv/cc (if we are entering current limit they show CC on the display) but also when the regulator totally messes up ('unreg' is dsiplayed then).
 
To turn a channel 'off' they do not simply program to zero...i forgot the exact trick , i'd have to look back at schematics. I know they had a software bug in firmare 1.1 and 1.2 where the supply would give -0.3 volts at 30 milliampere if you turned a channel off. Later software fixed that but you can't swap software easily. It's flash rom but not uploadable, you need to pop the chip out and make sure you have the right firmware for the display. These things have been in production so long that at one point the high voltage display controller went obsolete. They did a revision but the scanning is slightly different and the 80196 needs to know that . A 1.4 firmware is bug fixed with old display, the 2.xx firmware is for new display. Agilent publishes repair notes that you can download for free with all this stuff in it. They also publisch service manuals with a full description and explanation of all the techniques used.

Wanna really learn electronics ? Go read and study all Service manuals from HP /agilent equipment and look at the schematics.. You will be amazed at what kind of a goldmine you are sitting on!
« Last Edit: May 30, 2012, 02:26:50 am by free_electron »
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Offline Bored@Work

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #7 on: May 30, 2012, 12:22:43 am »
Now, the dac is another interesting beastie ...
They use a 16 bit dac to do the setting of all voltages and currents. The dac has a multiplexer on the output followed by analog memories built around tl074 and capacitors
They continously replenisch the caps by scanning and reprogramming the dac.

Sample and holds synchronized with the multiplexer's output.

I have recently seen that in a DIY powers supply. The S&Hs were driven with a PWM signal from an AVR CPU via a multiplexer. I didn't get the reason for this, since DACs are easy to get and use. But now that you mention it, the developer might just have copied an old design.
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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #8 on: May 30, 2012, 12:57:34 am »
Correct. Analog sample and holds that run in sync with a demux behind the dac.

Now, there is another thing i have not explained in my long 'post' above....
Calibration ! There is not a single potmeter in sight.... So how do you get all the nonlinearities and offsets out of this system...

Well this supply is self calibrating ! Another piece of genius from HP. The firmware has a calibration algorithm on board you can run this yourself. The password is 003631. Hold down one of the buttons on the frontpanel while powering up to enable cal mode ( forgot which button, bottom row, third from left i believe ) and use dial to enter password

WARNING ! DO NOT RUN THIS IF YOU DO NOT HAVE AN APPROPRIATE PRECISION VOLTMETER AND LOAD .

YOU NEED A 5-1/2 digit meter you can trust , both for voltage and current , and you need a dc load that goes up to 5 ampere.
Dave's load is ok , but you need an ampere meter with 5-1/2 digit... that can do 6 ampere...

Here is how calibration runs : the supply will make something it claims is 0.5 volts and ask you to measure the output. You simply enter the reading from you multimeter. It then does what it thinks is 5.5 volts and asks you to enter what you see on the multimeter. It goes on with the dual channel making 0.5,-0.5,19.5,-19.5.

And then it will ask you to draw 0.5 amp and 4.9 amp and 0.1 amp and 0.9 amp on the supplies. Each time you simply enter the number you see on your 'golden' multimeter.

And then .. Magic ! Using all the 'time' constants it has now accumulated from the multislope converter ( which measures averything as 'time') they run a vey clever bit of code that yields offset and gain for everything ! The calibrate the a/d , the linear optos , and any other offset or gain anywhere in the whole supply. This set of parameters is stored in a table and that's it.

The drawback is that you cannot 'measure absolute' in this system, which makes troubleshooting a bit hard sometimes, you can only see if something goes up or down but not absolute, only relative. In essence the A/D and the entire electronics is tuned to itself, all derived from a single 10 volts reference voltage that is converted to time on an integrator. This means that ,whenever you replace ANYTHING , even a simple resistor, the calibration needs to be run.

They don't even need accurate current sources.. They only need to be long term stable , the absolute precision is irellevant. Who cares if it is 1.078943 mA or 0.9983245 .. As long as it is long term stable we are ok. It is all tuned out during calibration. It's all just 'times' on an integrator. You can use cheap analog muxes with unknown rds on , your resistors can be 5% .. It all doesnt matter. You don't care about only one thing : long term stability of all parameters. The offset and gains, and tolerances are all calibrated out.

This multislope system is a very clever A/D. You can breadboard this. Someone on another forum ( i am active on another electronics forum too ...) wouldn't believe it could be that easy. He took two LF411 opamps out of the 'pile' , a temp stable capacitor for the integrator , put it on a breadboard in dead spider construction , hooked it to an FPGA he had laying around, wrote half a page of verliog code to make the counters... He used a simple voltage reference and he got 6 digit first try ! The damn thing was spot on compared to a 34401. There are some 'volt-nuts' on that forum that have super stable chemical references. So these guys got together , tweaked it a bit and compared the results to a solartron 8-1/2 digit... and they got 7 digits .. with two crap opamps , a capacitor and some counters breadboard in an afternoon ... beat that ... i don't know if they went beyond that. there was talk of trying it with ad711 and ad706 like the agilent uses , but i don't know if they ever did that.

I have seen HP do an automatic calibration on the supplies. ( they used to come once a year to do VOSCAL, their on site calibration service. If you have enough equipment they make house-calls. when i was at the factory we had enough stuff. the design center i work now has not enough to merit voscal )

They hook up two 3458 8-1/2 digit dmms , a shunt and a programmable load. They plug in gpib in the back and hit enter ... 10 seconds later .. A fully calibrated E3631 that is reliable down to 4 trailing digits...

Beat that with you 'pic' or 'avr' driving an lm317 with fancypants lcd display.

You'll have a very VERY hard time making a supply with the same specs (current / voltage / load response, readout accuracy and precision , floating outputs , gpib and serial control ) for even double the price of what the supply goes for new off the shelf at agilent.
The isolated floating outputs alone will kill you in cost.. Youll need one cpu per channel, send it through optos , have another earth referenced cpu and you wont even come close to the precision of control and readback... You need like 18 bits or more...

Agilent is the absolute king in this kind of stuff. Their designs are incredibly clever. Optimized in all aspects, some not immediately obvious. They do not 'overengineer'.. They do it 'right'. Apply the correct technique , cut costs but do not sacrifice performance or capabilities.

Another example is the 34401 multimeter. You can study that service manual for a whole week. The explanation on the converter alone is very very interesting.

Same with the 33120 and 33150 / 33250 signal generators. The DAC , filters and output stage is pure genius ! They have also a self calibrating system in there. Not a trimmer in sight. They can even calibrate the output impedance of the amplifier .

Those siglent , rigol and others dont even come close ! And they are 15 years more 'modern'...
« Last Edit: May 30, 2012, 02:01:28 am by free_electron »
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Offline A Hellene

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #9 on: May 30, 2012, 01:23:29 am »
For anyone interested, this is the full service manual with schematics (dated April 2000) for the Agilent E3631A, in a 6.25MB .PDF file.


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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #10 on: May 30, 2012, 02:23:04 am »
some more 'walkthrough'



from left to right :
-5 volt regulator in TO220 with 5 pins ( reset output for CPU )
- cable to the 6 volt supply. carries +/- 15 volt for analog opto servos and the volatage current set and readback signals.
- all the 'analog' drab between cable and the white 220nf caps is the multislope III convertor. U4 ( close to heatsink) is the input multiplexer. U5 ( under cable) is the referenc eucrrent multiplexer. the analog devices chip just above the connecotr i a buffer opamp making the + and - 10 volts reference from a chip that sits just left of the heatsink (U2).
- the 220nf capacitors and U9 + another under the cable ( hard to see ) are the 6 'analog memories ). U 13 is the demux for scanning them and the wide body analog devices chip is the DAC
next we have the sram and flash eprom.
-the big fat chips to the right are (bottom) the asic holding the digital part of the multislope converte, an extra uart for the frontpanel and the glue logic for the 80196 (that sits above it)


the business end ... bottom left ASI , bottom right 80188 .. ehh 80196 .. where di i get this 80188 from ? brainfart. need to go edit this ..
flash rom ( firmware 2.1 , so new display panel ) and 256k sram. the AD1851 is the 16 bit dac , u13 does the demux , r22 r24 r27 r25 r26 and the 220nf caps are the 'analog storage'


the A2211 opto on the left ( there is another one just outside the picture ) is for gpib/rs232. the next two are for CV/CC and UNREG detection (U13 does that : lm339) the HCNR200 are the analog optos. 4 in total. 2 outgoing , two returning : Vset, ISet, Vmeasured , IMesured
U14 is the 'current generator for the powertransistor. Q2 is the 'sink' that pulls current away from the source to regulate. U21 does the real work ... U20 U22 and U23 ( and the other one between the two left analog couplers U19) are the opto servo's. have nothing to do with supply regulation loop.

Here's a tip : wanna make a really good 'analog' power supply ? go strip that section out and replace the analog optos with potmeters. it'll outperform the 5 billion stupid lm317 "wrongly implemented , half understood, can't regulate to zero and doesnt have adjustable current limit" schematics floating around on the interwebs...

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #11 on: May 30, 2012, 03:04:09 am »
i wish i could read all free_electron posts. genius! from what i read so far, valuable reference for later.
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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #12 on: May 30, 2012, 03:18:12 am »
learn dutch :) i got over 15000 posts on the dutch electronics forum ... i really need to get a life :)
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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #13 on: May 30, 2012, 04:09:00 am »
Thanks free_electron i learnt a shitload just by reading all these ...
We are witnessing a shitload of thought going into the power supplies
(A accomplished engineer is one that makes something better without making it more expensive)
« Last Edit: May 30, 2012, 04:20:33 am by DaveXRQ »
 

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #14 on: May 30, 2012, 04:47:17 am »
(A accomplished engineer is one that makes something better without making it more expensive)

and that is exactyl what Agilent is good at ! it didn;t cost them anything extra, they cut corners left and right and come up with a product with unbeatable performance at its pricepoint. You open the box and simply keel over at the staggering number of components in the design... but if you do the pricecalc it turns out it is cheaper to slap in 6 opamps , 6 resistors and six capacitors + a multiplexer under software control , than 6 DAC's....

They optimized the snot out of this thing withouth sacrificing performance.
HP : High Performance , Heavy Product, High Price ... That is when 'HP' was still 'HP' and Bill and Dave were still in charge...

If you really want to see their 'magic' at work : service manual of a 34401 ! Or if you can find it : a 3485.. That beast has been in production since the dinosaur age ... and is still the 'gold standard' when it comes to multimeters. Heck these are the machines that today are still used to 'calibrate' the calibrators ... and its a 30 year old design ! ( mid 80's )

That multislope technique is simply brilliant ( go read the patents on it .. this is why you don't find it on the market as a chip ... it is heavily patented and they don't licence ...).
You don't care about anything 'absolute', not even your reference.  The only key factor is long-term stability and low-tempco. Anything else is automatically nulled by the converter itself.
So you end up with a converter that needs no manual adjustment and can easily be replicated. Just assemble it with cheap off the shelf parts. The only key part is the integrator opamp ( low bias current on the inputs and stable ) ,the integrator capacitor (  agood quality foil or silver/mica cap ) and a precision comparator to find '0 charge'.

The system is autozeroing as well. the input stage can switch between 4 'signals' - a positive reference, a negative reference , 0 , and the to be measured signal.
Autonulling algorithm : switch to zero , wait a fixed amount of time , reset counters , switch to + ref , wait a fixed time , switch back to zero wait same fixed time ,  store residual count value.
the residual count + the count of the fixed time give you the offset in the convertor. done.
Measuring algorithm : zero the integrator , charge with fixed time from reference , switch to input , measure time needed to hit 'zero'.

Take all numbers ( residual count of autozero , charge time and measuring time as well as the 'reference times' stored during calibration ) and apply simple math ..
Calibration parameters are stored as 'numbers'. you don;t care about precision of anything. who cares if my reference voltage is 5.000001 or 4.78634.
I know that , if i apply exactly 5 volts at the input the 'time' for that is x this 'time' is my 'reference' ( i nothing in the machine has been changed since it was last calibrated)
So they store a 'time value' for what is'believed to be the internal '10 volts reference' as well as for the '-10 volts reference. And that's it.
Since it is a balanced system ( charge up , discarge back to zero ) even your crystal is allowed to drift ! the absolute frequency of the crystal doesnt even matter. It's all time ratios. If the crystal ticks a bit slower they charge longer . Charging is a fixed number of ticks.

need more digits ? sample faster in the same time window. Simply jack up the clock and charge count value. A matter of more flipflops and a larger number in the digital comparator that decide 'end of charge' cycle. So it scales beautifully with microscopically added cost...

So calibration is a matter of applying a known reference, storing 2 numbers and the machine can do the rest all by itself. For production and initial alignment this is a tremendous cost saver. you can calibrate the machine on all ranges , all units in under a minute. Fully automatic. Simply store 2 numbers for each possible configuration. They even store a different set of numbers if they switch between front and back terminals ... so contact resistances in relays and switches is even acommodated for. As for the cal setup : you only need a stable reference.. done. so that too is cheap.

The base principle (dualslope) is very old. even the icl7106 uses that ( as does the icl7035 and many other chips found in meters ) . the problem is that dualslope is slow and easuring time is dependent on the to be measured voltage. Multislope speeds that up by injecting known currents ( which are again stored as a 'time-ratio' ). What these current really are in terms of microampere is not important. al it matters is that you know : if i turn on this mosfet : i deduct this much 'time' for every clocktick i leave it 'on' from the count value.
When i hit zero charge ( the comparator toggles ) i know how many 'counts' are in the convertor , how many i 'forced' off and my autozero residual. Apply simple math...
Multislope II runs continuously and attempts to keep charge on the capacitor at 0. the rest is simply counters going up and down and looking at the delta's between current and previous you know where you are... so it is incredibly fast too. ( that's why some of these meters can do 10000 readings a second or more at high resolution with great repeatibility)

It is an amazing idea. Elegant , simple, and brilliant.
« Last Edit: May 30, 2012, 05:19:52 am by free_electron »
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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #15 on: May 30, 2012, 06:06:15 am »
That multislope technique is simply brilliant ( go read the patents on it .. this is why you don't find it on the market as a chip ... it is heavily patented and they don't licence ...).

Patents don't last forever. The stuff from the '80th and early '90th should have expired.

It is probably more because it is simpler and easer for One Hung Low companies to grap some cheap off the shelf IC from the '70th, copy the example circuit from the datasheet, remove everything they think isn't necessary (filter caps) or they can't afford (precision resistors) and mass produce it with unskilled labor.
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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #16 on: May 30, 2012, 06:21:27 am »
patents do expire , but the we are at generation 3 or 4 now. and every generation has been renewed. so it's been under patent quite a while ...
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Offline tinhead

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #17 on: May 30, 2012, 06:37:51 am »
remove everything they think isn't necessary (filter caps) or they can't afford (precision resistors)
and mass produce it with unskilled labor.

you made my day!
I don't want to be human! I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter ...
I want to reach out with something other than these prehensile paws and feel the solar wind of a supernova flowing over me.
 

Offline vl400

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #18 on: May 30, 2012, 11:59:30 am »
Thanks for the really good info free_electron, will never look at the supply the same again!
 

Offline codeboy2k

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #19 on: May 30, 2012, 05:43:43 pm »
Now, the dac is another interesting beastie ...
They use a 16 bit dac to do the setting of all voltages and currents. The dac has a multiplexer on the output followed by analog memories built around tl074 and capacitors
They continously replenisch the caps by scanning and reprogramming the dac.

Sample and holds synchronized with the multiplexer's output.

I have recently seen that in a DIY powers supply. The S&Hs were driven with a PWM signal from an AVR CPU via a multiplexer. I didn't get the reason for this, since DACs are easy to get and use. But now that you mention it, the developer might just have copied an old design.

The Rigol DS1052 does this too, using a single DAC to refresh 4-5 holding caps per channel, to set some levels , i.e. offset, gain, trigger level, etc
EEVBlog user A Hellene once posted his hand drawn schematics here on the forum. I can't seem to find the thread anymore.

I've not seen it anywhere else before I saw it first in the Rigol, and I thought it was pretty slick then; I haven't read the HP schematics but I will now.
It seems like HP did it first.
« Last Edit: May 30, 2012, 05:49:46 pm by codeboy2k »
 

Offline A Hellene

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #20 on: May 30, 2012, 06:04:24 pm »
Quote
I can't seem to find the thread anymore.
Here is it.


-George
Hi! This is George; and I am three and a half years old!
(This was one of my latest realisations, now in my early fifties!...)
 

Offline codeboy2k

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #21 on: May 30, 2012, 06:59:04 pm »
Quote
I can't seem to find the thread anymore.
Here is it.
-George
Thanks George! Beautiful hand drawn schematics!
 

Offline A Hellene

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #22 on: May 30, 2012, 07:41:25 pm »
You are welcome.
Hi! This is George; and I am three and a half years old!
(This was one of my latest realisations, now in my early fifties!...)
 

Offline saturation

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #23 on: June 01, 2012, 05:33:54 am »
Most excellent commentary free electron, kudos from me too.  I thought I was reading the 'theory of operation' section of the HP DMMs!

One quickie though, in the bold, you mean 3458a, yes?  I had to check the Agilent website as this DMM did not ring a bell.
If so, yes, 3458a was the culmination of the line of DMM beginning with the 3455a.

Thanks for the really good info free_electron, will never look at the supply the same again!

If you really want to see their 'magic' at work : service manual of a 34401 ! Or if you can find it : a 3485.. That beast has been in production since the dinosaur age ... and is still the 'gold standard' when it comes to multimeters. Heck these are the machines that today are still used to 'calibrate' the calibrators ... and its a 30 year old design ! ( mid 80's )
Best Wishes,

 Saturation
 

Online free_electron

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Re: Teardown: Agilent E3631A Power Supply (Picture Heavy)
« Reply #24 on: June 01, 2012, 05:54:36 am »
eh, yes 3458A . i have a lysdectic syldectic dylsectic dyslectic memory :)

HP service manuals should be mandatory reading lecture in EE courses... They also used to have something called 'bench briefs' ( no not underwear ). the whole collection is somewhere on the web. There they published inteview with their designers and highlighted the techniques used. extremely interesting reading material.

When i moved into my new townhome last year i got strange looks because i would sometimes sit at the pool on weekends and read these big HP service manual binders with fold out schematics... Now they're used to the nutty guy because they know where to go when theri pc or tv don't work ..
« Last Edit: June 01, 2012, 05:58:28 am by free_electron »
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