What determines whether a switching supply will properly drive a given load?

[Bob Larter]

The STAX energizer is an audio product, and it's unlikely any switching
circuits in it operate above 50kHz or so.

Not so. See if you can guess how it generates the HV it needs for the
electrostatic field.

 

[mike]

I think is the issue is "too much" load. The power supply operates a
Discman -- which draws 1/10 the current -- with no problem whatever. Ergo...

I don't have a peak-hold meter. However, I did measure the battery current
with a Fluke 87 -- it's around 180mA. But at the moment you connect the
battery, the digital bar-graph display goes WHAM!, all the way to the right
in a fraction of a second. I suspect the unit is drawing several times 180mA
at turn-on.

The AC adapter input is spec'd at 300mA -- presumably the maximum capacity
required, rather than the average drawn.

If I can find a matching plug/socket pair, I might experiment with small
series resistors (1 to 5 ohms) to see what happens. At the moment, it's not
a pressing issue.

You don't need a peak-hold meter.
You need a DC current probe and a dual-channel storage oscilloscope.
Conjecture is no substitute for measurement.

 

[William Sommerwerck]

You don't need a peak-hold meter.

You need a DC current probe and a dual-channel storage oscilloscope.
Conjecture is no substitute for measurement.

Agreed, absolutely. But I don't have a dual-channel storage scope. I'd love
to have one of those fency new ones with the LCD (???) displays, but I can't
justify the cost, because I don't use it enough. My 25-year-old Philips is
gathering dust, as it is.

 

[mike]

Agreed, absolutely. But I don't have a dual-channel storage scope. I'd love
to have one of those fency new ones with the LCD (???) displays, but I can't
justify the cost, because I don't use it enough. My 25-year-old Philips is
gathering dust, as it is.

Ok, then use a resistor as a current measurement and your scope in a
dark room.
You're gonna find it difficult to diagnose a problem if you can't be
bothered
to even attempt a look at the symptoms.

 

[William Sommerwerck]

You don't need a peak-hold meter.

Ok, then use a resistor as a current measurement and your scope
in adark room.
You're gonna find it difficult to diagnose a problem if you can't be
bothered to even attempt a look at the symptoms.

That's a pretty rude thing to say.

The original posting was a question about why most samples of a particular
switching supply would not turn on when powering a device whose drain was
well below the supply's stated capacity. There was no "problem", as such --
merely an issue of curiosity.

The conclusion was that there was sufficient current inrush to force the
switching supply to briefly cut off. I've since found that if I simply leave
the supply on, it will eventually "come 'round", though it might take 10 or
15 seconds.

 

[mike]

That's a pretty rude thing to say.

The original posting was a question about why most samples of a particular
switching supply would not turn on when powering a device whose drain was
well below the supply's stated capacity. There was no "problem", as such --
merely an issue of curiosity.

The conclusion was that there was sufficient current inrush to force the
switching supply to briefly cut off. I've since found that if I simply leave
the supply on, it will eventually "come 'round", though it might take 10 or
15 seconds.

Conclusions with no measurement are called conjecture.
My pet peeve with newsgroups is the massive amount of baseless
input that's presented as FACT.

Problem is that people asking the question probably can't sort
the good info from bad advice. If they could, they wouldn't have
needed to ask the question.

In a perfect world, all electronic designs would be "robust"
and every bit of advice would be good advice.
Sadly, it ain't so.

When you substitute part of a system without knowing
the issues and experience symptoms you didn't expect,
it's time to worry whether it's a good idea.

Conventional wisdom suggests you should beef up the current limit
so it doesn't cycle.
Be prepared for the possibility that the "correct supply" has
soft-limit features
that control the startup current and that substituting with one that
doesn't have a soft limit may prove very stressful to the system.
You might want to implement a softer limit rather than a harder one.

You have a scope...plug it in and find out what's happening.
A two-minute experiment is way better than all the baseless conjecture
you're gonna get here.