Keysight New instruments

[nctnico]

Well the HP 6032A does have a dedicated foldback button.

It works like a normal bench PSU normally, but if you push the foldback button the LED next to it lights up and this locks the PSU into the current mode of operation. If you are currently in CV mode and the supply hits CC mode then it will instead shut down and wait for the output to be disabled and enabled again. If you are in CC mode (say powering a big LED with a set current), push the foldback button and then disconnect the load, causing the PSU to go back into CV mode it will shut down too.

Such a feature is probably even more desirable on such a massive PSU that can supply 1kW 60V 50A.

That is not fold-back but 'electronic fuse' operation. AFAIK this is pretty much standard on all digitally controlled HPAK PSUs. On the E3631xA series it is called OVP and OCP.

[tautech]

Why is it that foldback current limiting isn't incorporated in a 'quality' PSU FFS, even a $30 SMPS has such a feature as it's hardly a new leading edge technology when it's been around for decades.

How would that be compatible with constant current mode? How is a outputing a random voltage at a random current going to help?  AFAIK foldback current limiting is used to limit the dissipation inside the PSU in case the heatsink is not big enough.

Experiment with your MCH K305D.
Sure it's not foldback yet even in max CC mode it limits the voltage so that the max current is maintained and it will do that indefinitely and not smoke, pop fuses or traces.

Also it's difficult to rationalise foldbacks when you have a variable current limit. I mean you can't go over-current. What if it's a CC source you want (charging SLAs). Foldback would be a problem.

Indeed if you exceed the foldback limit however with the PSU's I use for SLA's which are mostly 7AH or less you don't want to squirt too much current into them anyways and as they're near the bench they're easy to monitor draw and increase the voltage to the cyclic limit and watch the current draw drop away. Couple of weeks back I forgot and left a nearly charged 24AH SLA charging overnight set to 14.5V which was drawing just 10mA next morning. 

[exe]

Usually, taking radio power supplies as an example, you set the voltage to 13.8V and the crowbar to 15V. The specification for the load sets the voltage tolerance. Typically this is max input voltage of LDOs, capacitors, ICs etc directly connected to the supply considering power dissipation as well. Some things designed for say 9v input will quite happily run at 12v depending on how the internal power is arranged.

In you example with blown zener and output voltage skyrocketing. Do you propose to have a second reference that would only be used for crowbar?

There are two cases where the crowbar comes in handy as well which are almost never mentioned as well. Firstly, and this does happen with RF stuff, when there is RF noise on the sense lines to the supply. Secondly, when the load is too inductive and the supply starts oscillating. Even the best of power supplies can be coaxed into oscillating (try running something like an SMPS on the end of a few metres of untwisted wire.

In both example, when crowbar fires the output drops to zero, is that correct? I'm not sure how useful is that, the load remains with no power. Probably, very special cases. If PSU is oscillating, the only way to "fix" it is to switch-off and do something about it. Like, adding more output capacitance, or reduce loop bandwidth, or use shorter wires, add filtering on sense wires, or something.

As of oscillating, I was thinking if power supply can detect that. I considered using window comparator, or ideal diode bridge and AC-coupling to rectify and sense peak-to-peak voltage, but it was too much added complexity to my liking. Probably, digitally sampling output voltage and processing in software is easier, but might be not as fast as a hardware solution.

I was also considering not a crowbar, but a down-programmer (essentially a load resistor triggered by comparator when output voltage, say 5%, above set voltage). Also quite tricky to make everything nice, fast and stable.

PS I'm currently making a power supply, and I made CV feedback with adjustable bandwidth: fast and slow. Slow is to drive troublesome loads. Also helps with stability at low output currents (below 1mA) when output stage has too much gain. I think a few commercial power supplies too offer switchable speed.

[Berni]

Well the HP 6032A does have a dedicated foldback button.

It works like a normal bench PSU normally, but if you push the foldback button the LED next to it lights up and this locks the PSU into the current mode of operation. If you are currently in CV mode and the supply hits CC mode then it will instead shut down and wait for the output to be disabled and enabled again. If you are in CC mode (say powering a big LED with a set current), push the foldback button and then disconnect the load, causing the PSU to go back into CV mode it will shut down too.

Such a feature is probably even more desirable on such a massive PSU that can supply 1kW 60V 50A.

That is not fold-back but 'electronic fuse' operation. AFAIK this is pretty much standard on all digitally controlled HPAK PSUs. On the E3631xA series it is called OVP and OCP.

Yeah i don't like the name they gave that feature since it is misleading, i guess its to not confuse it with the actual OVP feature of this PSU that is separate feature on a separate control. But the use case is similar to limit damage when something goes wrong.

And yes lots of bench power supplies have OVP and OCP settings, but on all of the ones i used was it a UI pain in the ass to set up. Most of the time you have to manually set a OCP limit somewhere and then make sure your current limit is set higher so that it actually reaches OCP and trips out. Then once you don't need it anymore you forget to turn it off, and be confused what is going on later on.

On the other hand on this PSU there is nothing that needs setting. You just use the PSU as normal and if you want this fuse like trip out protection you simply press that foldback button and see the LED light up to indicate its active. If you don't need it anymore simply press the button again and it turns off. I want this "magical act like a fuse button" on all of my PSUs but none seam to actually implement one.

[Kleinstein]

The classical crowbar circuit uses a beefy SCR. So one fired it will essentially short the output to some 1.5 V residual voltage of the SCR. One would even need to turn off the ouput before the SCR would go open again.

Detection of oscillation would be a nice feature, but it is far from standard.  A good lab supply with simple outputs should not oscillate with any reasonable passive load. A few not so good ones get unstable with large low ESR caps, or maybe high Q resonant loads. With seprate sense wires one can hardly avoid oscillation if the sense wiring is poor.
The critical case for the CV mode is a capacitive load and even if not oscillating there can be quite some ringing with a tricky load. Naturally a regulated supply has a inductive ouput impedance over a larger frequency range.

A SMPS may very well show negative differential input resistance - worst case it may even oscillate when powered from a battery with long enough cables.
So the combination of poor SMPS and lab supply may show oscillation and ripple.

[Berni]

There are two cases where the crowbar comes in handy as well which are almost never mentioned as well. Firstly, and this does happen with RF stuff, when there is RF noise on the sense lines to the supply. Secondly, when the load is too inductive and the supply starts oscillating. Even the best of power supplies can be coaxed into oscillating (try running something like an SMPS on the end of a few metres of untwisted wire.

In both example, when crowbar fires the output drops to zero, is that correct? I'm not sure how useful is that, the load remains with no power. Probably, very special cases. If PSU is oscillating, the only way to "fix" it is to switch-off and do something about it. Like, adding more output capacitance, or reduce loop bandwidth, or use shorter wires, add filtering on sense wires, or something.

As of oscillating, I was thinking if power supply can detect that. I considered using window comparator, or ideal diode bridge and AC-coupling to rectify and sense peak-to-peak voltage, but it was too much added complexity to my liking. Probably, digitally sampling output voltage and processing in software is easier, but might be not as fast as a hardware solution.

I was also considering not a crowbar, but a down-programmer (essentially a load resistor triggered by comparator when output voltage, say 5%, above set voltage). Also quite tricky to make everything nice, fast and stable.

PS I'm currently making a power supply, and I made CV feedback with adjustable bandwidth: fast and slow. Slow is to drive troublesome loads. Also helps with stability at low output currents (below 1mA) when output stage has too much gain. I think a few commercial power supplies too offer switchable speed.

Yep this is why some of the HP supplies i mentioned have current sinking capability. As soon as you try to raise the voltage it starts to sink it to ground, staying in regulation without any jerky step response.

Adjustable bandwidth is a lot more rare but some do have it. For example the HP/Agilent 66332A has a 'Fast' and 'Slow' switch on the back. This is likely because this PSU is specialized for a fast response since it is capable of replaying voltage waveform from a buffer at up to about the rate of 100K samples per second. So it is likely also much more prone to oscillation compared to a regular PSU. To get this speed it  drives the output using a AB class amplifier output stage. So due to the constant biasing the heatsink gets fairly warm even when it is outputting zero amps.

[bd139]

Usually, taking radio power supplies as an example, you set the voltage to 13.8V and the crowbar to 15V. The specification for the load sets the voltage tolerance. Typically this is max input voltage of LDOs, capacitors, ICs etc directly connected to the supply considering power dissipation as well. Some things designed for say 9v input will quite happily run at 12v depending on how the internal power is arranged.

In you example with blown zener and output voltage skyrocketing. Do you propose to have a second reference that would only be used for crowbar?

There are two cases where the crowbar comes in handy as well which are almost never mentioned as well. Firstly, and this does happen with RF stuff, when there is RF noise on the sense lines to the supply. Secondly, when the load is too inductive and the supply starts oscillating. Even the best of power supplies can be coaxed into oscillating (try running something like an SMPS on the end of a few metres of untwisted wire.

In both example, when crowbar fires the output drops to zero, is that correct? I'm not sure how useful is that, the load remains with no power. Probably, very special cases. If PSU is oscillating, the only way to "fix" it is to switch-off and do something about it. Like, adding more output capacitance, or reduce loop bandwidth, or use shorter wires, add filtering on sense wires, or something.

As of oscillating, I was thinking if power supply can detect that. I considered using window comparator, or ideal diode bridge and AC-coupling to rectify and sense peak-to-peak voltage, but it was too much added complexity to my liking. Probably, digitally sampling output voltage and processing in software is easier, but might be not as fast as a hardware solution.

I was also considering not a crowbar, but a down-programmer (essentially a load resistor triggered by comparator when output voltage, say 5%, above set voltage). Also quite tricky to make everything nice, fast and stable.

PS I'm currently making a power supply, and I made CV feedback with adjustable bandwidth: fast and slow. Slow is to drive troublesome loads. Also helps with stability at low output currents (below 1mA) when output stage has too much gain. I think a few commercial power supplies too offer switchable speed.

The point is to protect the load so return it to the safe condition of "unpowered". The point of the crowbar is to blow something upstream that is more permanent i.e. a fuse.

Regarding the conditions mentioned, usually you twist the power leads together as that gives some common mode isolation or move the regulation closer to the load.

[balage]

Here is something about the original thread.
Do you see the screen of the instruments? At the bottom. Is that a windows bar? What da...
But it is interesting the picture is smooth everywhere except the screen that is sharp. They must have photoshopped the Windows bar down there. 
They are freakin' playing with us.
The pic is from a facebook post.

Edit: The bottom right is the scope with so an unlikely screen. Also the Run/Stop button is not active with the Single button in the same time.

[Someone]

Nice catch, probably screenshots from a UI simulator running on a PC. Then its down to the graphic designer/artist who doesn't fully understand the products and whoever approved the image.

[Keysight DanielBogdanoff]

Here is something about the original thread.
Do you see the screen of the instruments? At the bottom. Is that a windows bar? What da...
But it is interesting the picture is smooth everywhere except the screen that is sharp. They must have photoshopped the Windows bar down there. 
They are freakin' playing with us.
The pic is from a facebook post.

Edit: The bottom right is the scope with so an unlikely screen. Also the Run/Stop button is not active with the Single button in the same time.

  You found it! I was wondering if that would get mentioned. Each of these will have a dedicated Windows app/.exe for remote control / logging etc. I was involved in this shoot, and we did it all with the screens off/blank (there's nothing connected to any of the inputs). We did have a shot of them booting up, but decided to not try to get anything pretty on screen. That's where my involvement ended. Well, it was decided to add screenshots/screens in post and this is what they were given/used.

For a promo/teaser image I think it's fine, but THE GEAR DOES NOT RUN WINDOWS ON THE BOX, it's all embedded OS stuff. Any of these silhouette images with LEDs/front panel lights one are almost certainly grabbed from the boot LED sequence and not actual run-time modes.

[EEVblog]

Here is something about the original thread.
Do you see the screen of the instruments? At the bottom. Is that a windows bar? What da...

Top notch community trolling from Keysight! 

[jjoonathan]

Hey are you sure you didn't include the new secret instrument by mistake in that photo?

[Keysight DanielBogdanoff]

Here is something about the original thread.
Do you see the screen of the instruments? At the bottom. Is that a windows bar? What da...

Top notch community trolling from Keysight! 

You know, we gotta keep the bar high

@jjoonathan gah can you imagine trying to go back to frog legs? Or ox heads?

[tszaboo]

I think a fuse would be a good idea to have on a PSU with such a SCR crowbar circuit.

Its not even that difficult to get around the fuse voltage drop. All you do is hook up the sense wire after the fuse. Since the voltage sense is a high impedance input it is a lot easier to protect it using the good ol resistor and TVS diode.

Tho that fuse then only protects the PSU from the DUT. If the crowbar trips because of a fault inside the PSU it wont blow, but then again at that point you need an extensive PSU repair anyway, and a common fault with linear PSUs that makes them output too much voltage is a blown pass transistor, so your power stage is already dead anyway, eventually a fuse at the transformer would blow to stop it from catching fire.

No. A large lithium battery can easily supply 1000A if short circuited. You would need a fuse with 1000A DC breaking capacity. Fast acting, because you want to protect semiconductors with it.
And then you realize that fuses are not meant to be used to protect semiconductors, they are there to protect wires from catching fire. A power supply is not a charger.

[SilverSolder]

[...] A power supply is not a charger.

Once you go down this road, you can equally argue "A power supply is not a diode tester", "A power supply is not a LED driver",  "A power supply is not a TEK module driver", and any other specific thing you are doing with it?

I have always viewed a lab power supply as a general purpose source of power with variable voltage and variable current -  what I do with that voltage and current is surely up to me?

[bd139]

A scope is not a multimeter or a spectrum analyser either. But it’s a good compromise. Which is the point of a power supply.

[bdunham7]

No. A large lithium battery can easily supply 1000A if short circuited. You would need a fuse with 1000A DC breaking capacity.

That would be a standard AGC glass fuse at 32VDC, with sub-millisecond fusing time.  And even with an 8S pack of 'huge' batteries, the combined series resistance of the battery, wires and crowbar circuit including traces would have to be 32mR or less for 1000 amps to flow for that millisecond. 

Fast acting, because you want to protect semiconductors with it. And then you realize that fuses are not meant to be used to protect semiconductors...

That's a pretty broad statement, especially considering the range of products that are called 'semiconductors'.  Fuses can--and commonly do--protect semiconductors just fine in a properly designed circuit, with obvious limitations.  For a crowbar, if the impedance of the crowbar is just high enough so that the peak current doesn't exceed the SCR peak rating (which can be 1000 amps without using anything extraordinary) then the fuse just has to blow before the SCR melts.  Not difficult at all to understand or design.

A power supply is not a charger.

Again, a very broad statement.  Mine are suitable for battery charging.  It says so in the manual.  They don't use a crowbar for OVP though, that seems to be suboptimal for battery charging.  Actually, to me it seems suboptimal in general.

[tszaboo]

No. A large lithium battery can easily supply 1000A if short circuited. You would need a fuse with 1000A DC breaking capacity.

That would be a standard AGC glass fuse at 32VDC, with sub-millisecond fusing time.

I'm sorry to tell you, but the only information in your comment is that you dont understand the rating of fuses. Look up the difference between AC current rating, and DC current rating of a fuse, and why they are different.
https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-agc-fast-acting-glass-tube-fuses-data-sheet.pdf
Before you start searching for it: No it doesnt have a DC rating at all. Moving on.

[bdunham7]

I'm sorry to tell you, but the only information in your comment is that you dont understand the rating of fuses. Look up the difference between AC current rating, and DC current rating of a fuse, and why they are different.

Condescending snark isn't helpful.  I fully understand why AC and DC interrupt ratings are often, but not always, different.  But I think the datasheet you posted has some errors, unless you would like to explain why a fuse current interrupt rating would go down with a lower voltage--if you can explain that I would truly learn something.  Here is the previous version:

https://www.grainger.com/ec/pdf/6F018_1.pdf

Fuses in automotive applications, especially 24/28 volt systems in larger vehicles, have to deal with some pretty high fault currents and they use AGC (old) and ATO (new) plain fast-blow fuses without any trouble.  I think 1kA was pretty standard for 32VDC AGC fuses although I don't have a datasheet handy, and I don't think it makes much difference if it is AC or DC.  (Perhaps you can guess why?) If that's not convincing or if you demand an explicit DC interrupt rating in a datasheet, just find a different fuse with the rating you want.

https://www.mouser.com/datasheet/2/240/Littelfuse_Fuse_314_324_Datasheet_pdf-756861.pdf

Edit:  and here is a datasheet for a modern automotive-style ATO fuse that explicitly states 1kA@32VDC

https://www.mouser.com/datasheet/2/240/Littelfuse_ATOF_Datasheet-523209.pdf

[ResistorRob]

Nobody has posted the teaser video?
I really like the interconnectivity between instruments and available apps for each instrument.

[wizard69]

[...] A power supply is not a charger.

Once you go down this road, you can equally argue "A power supply is not a diode tester", "A power supply is not a LED driver",  "A power supply is not a TEK module driver", and any other specific thing you are doing with it?

I have always viewed a lab power supply as a general purpose source of power with variable voltage and variable current -  what I do with that voltage and current is surely up to me?

Sure it is up to you but at the same time many power supplies are not designed for such usage.   On the flip side special purpose power supplies for battery charging exist and are widely available.   Considering that battery chagrining leads to fire more often that is should, making use of a supply designed for such usage is a wise move.

[SilverSolder]

[...] A power supply is not a charger.

Once you go down this road, you can equally argue "A power supply is not a diode tester", "A power supply is not a LED driver",  "A power supply is not a TEK module driver", and any other specific thing you are doing with it?

I have always viewed a lab power supply as a general purpose source of power with variable voltage and variable current -  what I do with that voltage and current is surely up to me?

Sure it is up to you but at the same time many power supplies are not designed for such usage.   On the flip side special purpose power supplies for battery charging exist and are widely available.   Considering that battery chagrining leads to fire more often that is should, making use of a supply designed for such usage is a wise move.

It is best to understand the limitations of your power supply - RTFM - almost no matter what you use it for, to avoid nasty surprises.

It is always "technically best" to use specific devices, but it may not be "practically best" - if you only charge a particular battery once a year that doesn't fit in your regular AA charger, you are not being totally crazy by using the tools you already have, instead of burning the planet resources on stuff that will hardly ever get used, right?

[wizard69]

Nobody has posted the teaser video?
I really like the interconnectivity between instruments and available apps for each instrument.

Interesting video but not enough info!   I could use the scope offering, maybe even some of the other instruments.   

As for apps, if HPAK is just doing Windows I'm not going to be all that happy.

[Berni]

[...] A power supply is not a charger.

Once you go down this road, you can equally argue "A power supply is not a diode tester", "A power supply is not a LED driver",  "A power supply is not a TEK module driver", and any other specific thing you are doing with it?

I have always viewed a lab power supply as a general purpose source of power with variable voltage and variable current -  what I do with that voltage and current is surely up to me?

Sure it is up to you but at the same time many power supplies are not designed for such usage.   On the flip side special purpose power supplies for battery charging exist and are widely available.   Considering that battery chagrining leads to fire more often that is should, making use of a supply designed for such usage is a wise move.

You don't always have a charger on hand for every single thing. For example do you have a battery charger for 9V block Ni-MH batteries?

Most chargers do the same thing a bench PSU does anyway. Supply a constant voltage with a current limit. Also there are cases where you might need more control over a charger that just on/off. One example is a battery test rig i cobbled together from a PSU and electronic load connected to a PC. It was used to generate test scenarios for a few battery monitoring systems that ran various types and sizes of lead acid batteries up and down for weeks non stop. For this i needed a battery charger that can easily be told by a PC to charge a battery in various different conditions. Such a thing is a lab PSU with SCPI control. But i did blow up one PSU during those tests, however it was not because the big ass deep cycle lead acid battery would feed power back into it, it was simply a cheep Tenma brand PSU from Farnell. Its cooling was apparently too poor(despite having a fan and no obstructions) and so after outputting a lot of current for a while the pass transistors gave up the ghost, my SCPI software even captured a graph of its death over the course of a few seconds as the output regulation went erratic before shooting up. I had a diode in place, but it was mostly to keep the internal dummy load resistor inside the PSU from discharging the battery when the PSU was turned off, i also had a fuse between the battery and test rig in case something blew up and the battery dumped all its might into it. I replaced the PSU with a better quality BK Precision PSU and it was running fine.

So the actual risk here was that the died PSU went out of regulation and if unchecked would overcharge the battery to destruction. Luckily lead acid cells don't mind it that much, NiCD and NiMH can take overcharge too as long as the current is not too high. Any LiFePo cells might be damaged but not cause any issues otherwise, most batteries don't catch fire even if you try so. But if it was a Li-Ion Li-Po etc this could have indeed ended ended up a pretty serious fire.

[Fungus]

Nobody has posted the teaser video?

Interesting video but not enough info!

That's the definition of a "teaser".