Re: What is the meaning of ULU? Topic was: 7000-series power-hungry plug-ins

Harvey White

On Sat, 13 Oct 2018 19:32:21 -0700, you wrote:

I love the definition of "Fold Back Current Limiting " ...Dennis you are
so right, the fuse always survives...LMAO....thanks I needed that...
Renée, K6FSB
What happens in a technical sense is that the circuit is set up with a
(much lower) short circuit current limit. When the overcurrent
happens, the circuit "folds back" to the point where the maximum
current is the foldback limit. To get it to reset, you generally turn
power off and reapply power.

There's a particular setup in the uA723 regulator (yeah, old
nomenclature) that is available for that.

An example would be that you have a 5 volt supply at 1.5 amps,
foldback to 300 ma.

Voltage is reduced, of course, to maintain that maximum current.

The old data sheets for the UA723 would show that circuit. A nice
thing is that these regulators show up in Tektronix equipment.

and I *think* that a suitable quote runs something like this:

Fuse: an inexpensive part designed to fail to protect a circuit; is
always protected by an extremely expensive part that will fail first
in order to protect the 25 cent fuse.


On 2018-10-13 05:49 PM, Dennis Tillman W7PF wrote:
On behalf of all of us thank you Håkan once again.

Of course I know what Fold Back Current Limiting is. In its simplest terms it is a circuit that prevents you from burning up a valuable instrument while you are tinkering around inside it with a screwdriver or other metal tool. One of Murphy Law's guarantees that the more careful you are, the more catastrophic the damage you will cause. Fold back Current Limiting is designed to sacrifice active devices such as transistors and ICs in order to protect the fast blow fuse from stress.

"tinkera123" also asked what the acronym ULU meant. I was hoping someone would explain it. The specific sentence it is used in doesn't give much to go on:
"Some suggestions for the wiring interface to the ULU are offered."
This is followed by 5 suggestions.

From the suggestions it sounds like they are talking about a Device Under Test but the well-known acronym for this is DUT. Some companies use Unit Under Test or UUT.
So far no one has offered an explanation for ULU. I can't think of anything that fits those letters and there are very few ULU acronyms.

The closest I could up with is Unit Under Load which might mean a set of standard load resistors attached to a male connector that plugs into the backplane and loads the power supply enough to draw the maximum amount of power from each supply that the slot should be able to supply. But a Unit Under Load would be UUL. As anyone who plays Scrabble knows, the order of the letters can be really important.

Dennis Tillman W7PF

-----Original Message-----
From: [] On Behalf Of
Sent: Friday, October 12, 2018 3:34 PM
Subject: Re: [TekScopes] 7000-series power-hungry plug-ins

Regarding this pdf of 7000 series currents ..... I am unfamiliar with the
terms Foldback currents and ULU.
Can some-one please explain??

-Chuck Harris

PS, thanks to Håkan for the 7904 power supply capacity note.

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