Author Topic: Keysight New instruments  (Read 9931 times)

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Offline bdeianov

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Re: Keysight New instruments
« Reply #175 on: Yesterday at 01:58:51 am »
Or just stuff a diode in series.  :-//

That's what the manual tells you to do.
Unfortunately no external sense to compensate for the drop.

I was curious what the E36312A / E36313A supplies do, which do have remote sense. Turns out they have the same note in the manual. They further show the sense line connected before the diode, so they still can't compensate for the diode drop.
 

Offline Berni

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Re: Keysight New instruments
« Reply #176 on: Yesterday at 06:31:06 am »
Same thing is recommended for the rack mount system PSUs 6621A, 6622A,6623A, 6624A,6627A



But i have feed voltage back into one of these supplies and it behaved nicely. If you try to pull the output voltage above what it is set to it simply starts sinking current to keep it in regulation. I have even used it as a "battery simulator" on a power bank and it was perfectly happy both providing current and sinking current. The sinking ability appeared to be limited by the channels maximum rating. So if you had a 60V 1A channel it would sink up to 1A of current before the voltage goes out of regulation. All this is done in analog circuitry and works well. So yes it does sink current but it would just slowly discharge the battery.

However the manual there talks about OVP specifically. This is a feature that is off by default and you have to manually turn on using a button. I have not tested that, but i would assume it does the usual sinking up to the channel maximum, but if you shove in more current that the channel can handle then the voltage starts to rise, eventually hitting the (likely in hardware) OVP trip point. At this point it would make sense for the PSU to fire off a SCR across the output to short it out in a last ditch attempt to keep the voltage from rising too high.

Most other PSUs have an internal pre-load resistor across the output that is behind the current sense shunt. This resistor mostly being there to discharge capacitors and help the linear regulator be more stable. So as a result most PSUs do have sinking capability but only in the 10s of miliamps (depends on the voltage)
 
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Offline 2N3055

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Re: Keysight New instruments
« Reply #177 on: Yesterday at 07:16:18 am »
Problem here is specifically in crowbar circuit. PSU that are more than one quadrant, or have active down programmer have current limit and won't be damaged. Most of the PSU are specced for parallel mode, and if they are, they are designed to back fed the voltage.  Problem is only if crowbar circuit fires, or you reverse voltage, and that only if outside source (battery) can source too much current ( which decent sized SLA or LiIon or LiPO can) so there is damage.

Bottom line, we all on occasion charge batteries on those lab PSU, but they are not meant to do so...
If I do, I put big Schottky diode in series and raise voltage 0.5V. That's close enough for charging.
Or I could put in mosfet protection reverse voltage circuit  and not worry about voltage drop at all. That one could be put in a small box with cables on and you just grab charging cables and connect battery...
It's just I don't do this often enough  to be bothered to make one...
 

Online tautech

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Re: Keysight New instruments
« Reply #178 on: Yesterday at 07:34:29 am »
If a lab PSU isn't safe to charge any battery it's not worth the scrap metal it's made from !  :P

At power loss it should default to output OFF unless it has an option to override this.
OVP need also be selectable and enabled as necessary where instead of blowing fuses it should trigger the output to OFF.

None is magic and are standard features in some PSU's.
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Offline Bud

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Re: Keysight New instruments
« Reply #179 on: Yesterday at 07:52:26 am »
Those rack mountable HP power supplies "can" sink current but that was not meant to serve as electronic load, and their operator's manuals say that. Current sink feature was meant for programmable testing, such as evaluating Load's regulation and transient response. A program would run via GPIB, making the power supply change voltage fast. When such changes go from higher voltage to lower voltage , the power supply has to be able to sink current from charged capacitors on the Load side.
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Offline bd139

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Re: Keysight New instruments
« Reply #180 on: Yesterday at 08:01:18 am »
Or just stuff a diode in series.  :-//

That's what the manual tells you to do.
Unfortunately no external sense to compensate for the drop.

I was curious what the E36312A / E36313A supplies do, which do have remote sense. Turns out they have the same note in the manual. They further show the sense line connected before the diode, so they still can't compensate for the diode drop.

What about using a MOSFET as an ideal diode circuit instead of just a diode?
 

Offline 2N3055

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Re: Keysight New instruments
« Reply #181 on: Yesterday at 09:01:29 am »
Or just stuff a diode in series.  :-//

That's what the manual tells you to do.
Unfortunately no external sense to compensate for the drop.

I was curious what the E36312A / E36313A supplies do, which do have remote sense. Turns out they have the same note in the manual. They further show the sense line connected before the diode, so they still can't compensate for the diode drop.

What about using a MOSFET as an ideal diode circuit instead of just a diode?
See my post above
 
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Offline bd139

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Re: Keysight New instruments
« Reply #182 on: Yesterday at 09:05:02 am »
That'll teach me for not reading all the posts  :-+
 
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Offline Fungus

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Re: Keysight New instruments
« Reply #183 on: Yesterday at 09:43:23 am »
Some supplies have a fuse...

My $35 FNIRSI even came with with two spares in SMD tape:)



Or just stuff a diode in series.  :-//
That's what the manual tells you to do.

Let's hope the students remember to do that.  >:D
 

Offline nctnico

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Re: Keysight New instruments
« Reply #184 on: Yesterday at 10:44:13 am »
If a lab PSU isn't safe to charge any battery it's not worth the scrap metal it's made from !  :P
Nonsense. For charging batteries you use a battery charger which is suitable for the chemistry. A lab PSU is the wrong tool for battery charging so don't be surprised it is not 100% suitable for that purpose. The function of overvoltage protection / crow bar is to protect your potentially expensive DUT (a prototype SoC board can easely cost US $1000) against operator error or defects inside the PSU.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline Fungus

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Re: Keysight New instruments
« Reply #185 on: Yesterday at 10:49:00 am »
If a lab PSU isn't safe to charge any battery it's not worth the scrap metal it's made from !  :P
Nonsense. For charging batteries you use a battery charger which is suitable for the chemistry. A lab PSU is the wrong tool for battery charging so don't be surprised it is not 100% suitable for that purpose. The function of overvoltage protection / crow bar is to protect your potentially expensive DUT (a prototype SoC board can easely cost US $1000) against operator error or defects inside the PSU.

Battery protection modules are about $0.15 on Aliexpress: https://www.aliexpress.com/wholesale?SearchText=TP4056


 

Online SilverSolder

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Re: Keysight New instruments
« Reply #186 on: Yesterday at 01:24:59 pm »
[...] A lab PSU is the wrong tool for battery charging [...]

Is that totally fair?  -  a lab PSU is a general purpose source of power that shouldn't really care what you use it for (within reason!).  A battery charger is an application specific device.  So, I would accept that the charger is "better"...  but surely I should feel OK about connecting anything I like to my lab power supply that isn't directly insane? 

For example, the other day I was measuring the internal resistance of a bunch of NiMH cells.   My battery charger was not able to do this...  so I used my ancient lab power supply in constant current mode and measured the difference in voltage drop between two currents, differing by 200mA.   So, connecting a battery to the supply is a possible use case even if you are not charging it...   

Also, consider the use case of charging a supercap, or even a regular capacitor (massive capacitor bank in an audio amplifier, for example) and subsequently decide to lower the voltage...

Overall, it seems preferable to me that a lab supply is able to deal with these kinds of real world scenarios without the risk of self destruction.  Granted, a crowbar is always going to be an issue and probably should not be used without a fuse...  but that could also be baked in.



« Last Edit: Yesterday at 01:28:09 pm by SilverSolder »
 

Online bdunham7

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Re: Keysight New instruments
« Reply #187 on: Yesterday at 03:12:58 pm »
Nonsense. For charging batteries you use a battery charger which is suitable for the chemistry. A lab PSU is the wrong tool for battery charging so don't be surprised it is not 100% suitable for that purpose. The function of overvoltage protection / crow bar is to protect your potentially expensive DUT (a prototype SoC board can easely cost US $1000) against operator error or defects inside the PSU.

The manual for mine specifically lists battery charging as a function and gives details on how to do it.  A 'correct' charger is optimal for routine battery charging, but people do test/repair/characterize/analyze/etc battery systems just like anything else and there are many times I'm interested in more than just charging the battery.  Other times I may need to charge and internal or odd battery in order to test something and the 'correct' charger is broken or unavailable.  It's an everyday use for me and I can't think of anything that would work better.

 It doesn't have a separate OVP, but designing an OVP should be straightforward and properly implemented it shouldn't result in damage if you connect a battery.  In non-battery situations where the OVP is there to protect your SoC from programming errors or internal control circuit failures, triggering the OVP should result in a current-limited internal short or, if the current-limiting part fails, a blown internal fuse.  Triggering the OVP while a battery is connected should result in a blown fuse.  Whether or not the PSU is capable of sinking current (mine does not) shouldn't matter much to a good OVP design.  If you don't need or want battery charging capability then it is fine to buy a PSU that 'fails' the battery test, but there isn't any inherent conflict that I can see between the two goals of protecting your SoC and not going up in flames if someone connects a battery.
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Offline nctnico

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Re: Keysight New instruments
« Reply #188 on: Yesterday at 03:32:30 pm »
Now try to figure out how HP never came up with the idea of having a fuse in series with the output of a PSU ^-^
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline exe

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Re: Keysight New instruments
« Reply #189 on: Yesterday at 03:38:19 pm »
Disagree entirely. Crowbar is important when the following equation is true:

cost_of_load > cost_of_power_supply

A year or so ago I had what i consider to be a fairly decent quality supply (HP) blow the reference zener. This caused the output to bang itself at the collector supply voltage. You should plan for such failures.

How does a crowbar work? I assume the expensive load is also sensitive to overvoltages. In this case the crowbar should engage very fast and at voltages not so much above the set voltage. If reference circuit doesn't work,  how does the crowbar know when to trip?

If crowbar set to trip at, say, 30V, then it's already late, imho.
 

Online SilverSolder

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Re: Keysight New instruments
« Reply #190 on: Yesterday at 03:47:38 pm »
Now try to figure out how HP never came up with the idea of having a fuse in series with the output of a PSU ^-^

I guess you'd have to sense the voltage on both sides of the fuse to do a really good job...  it starts to get expensive!  :D
 

Offline HighVoltage

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Re: Keysight New instruments
« Reply #191 on: Yesterday at 05:44:58 pm »
The problem I have with crowbar is that I did not know about it, until I read the manual. :-DD

The brand new Agilent PSU that I killed a few years back, was a E3648A series PSU.
The heavy crowbar traces were burned away completely.
Luckily the traces could be repaired with heavy copper wires.
Now I am aware !


 
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Online bdunham7

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Re: Keysight New instruments
« Reply #192 on: Yesterday at 06:37:10 pm »
Now try to figure out how HP never came up with the idea of having a fuse in series with the output of a PSU ^-^

You tell me. Some other manufacturers have them, some don't.  I've worked on quite a few bench PSUs in recent years and although later model HPAK PSUs like the E36xx series are expensive and widely held in high regard, they don't impress me all that much.  There's no reason to let them go up in flames rather than simply have a large fuse to protect against gross overloads.  Or simply use an OVP system other than a crowbar.
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