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

That's what I suspected. However, the energizer is not a "light" load -- it runs slightly warm. Whereas the CD player draws next to nothing, and the supply has no problem with it.

Nevertheless, I might just stick a 200 ohm resistor across the power jack, just to see what happens.

Perhaps a few hundred mF as well ??

"William Sommerwerck"

Problem is, SMPSs usually have over-current protection which typically shuts the supply down pronto - then it may try to re-start itself. Hence the hiccupping noise.

OTOH - a battery supply or iron transformer supply can provide brief bursts of high DC current that few small SMPSs can manage.

.... Phil

I agree with other comments WRT a high initial load causing the SMPS to current-limit or shut down.

A couple of 12V 15A SMPSs I had recently, would fail to start up when a high initial load was connected to them. I was using a dual-beam halogen headlight lamp for a load, and the SMPS would start up with either lamp connected, but not both. They would try to restart after a brief pause, but not start up.

The load of the hot lamp filaments was about 5A and 3A, but higher with cold filaments. The SMPS was able to power both lamps by starting with one lamp, then adding the second (either one first) for extended periods with no problems.

These were used SMPSs, and I have no way to know if new ones would operate the same way, but I suspect that new ones would be the same.

Smart machines.. whaddaya gonna do? The protected output keeps end users out of the supply (maybe), since changing a fuse (or adjusting pots) won't change the rated output.

I don't know if adding a filtering electrolytic capacitor to the output would help, I haven't tried it. The solution may be to limit the inrush current to the STAX accessory.

Otherwise, get some over-2000 mAh NiMh AAs and a good charger, and carry freshly-charged spares. This has been the only reasonable solution for keeping my digital cameras portable.

-- Cheers, WB .............

That makes the most sense. Even with the supply that works, the red (low-voltage) light comes on for quite some time before the energizer switches to green, noticeably longer than batteries or the conventional power supply.

Thanks for the info. I have to decide whether I want to accept things as they are (I use the headphones fairly often, and am not sure want to carry around a pile of rechargeable batteries), or modify the energizer with (say) a 10-ohm series resistor.

Actually, I have a bunch of 2500 and 2750mAh AA cells, from PowerEx (MAHA). I use the MAHA C9000 charger, which I highly recommend. I have two, both of which were purchased when Thomas Distributing had them on sale. There's an (optional?) car-battery cable that permits "off line" recharging, a great help for those "in the field".

The only thing wrong with this charger is that it won't take C or D cells (MAHA refuses to produce adapters), so I use an Eveready nicad/NiMH charger that takes all sizes from AAA to D, plus 9V. It works well, but it doesn't have any of the C9000's features (choice of charging current, controlled discharge and conditioning, capacity measurement, etc).

My first digital camera was the Olympus D-620L (still have it -- I'll sell it for $100 to anyone who wants a cheap zoom DSLR for eBay shots, etc), which used loose AA cells. My newer DSLRs take custom Li-ion battery packs. I hope Olympus and Canon have the common decency to provide replacement packs for at least the next decade. If not, may they (and other camera companies) be struck with class-action lawsuits!

In case it hasn't been mentioned here... Do not purchase third-party Li-ion battery packs, even from well-known companies (eg, DigiPower). They simply do not last. Their capacities quickly decline and the charger starts blinking or reporting "battery won't charge". The ones I bought for my Yaesu VX-5R and Olympus E-500 "went bad" very quickly -- a complete waste of money. (The OEM batteries for both still work fine.)

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

Some switching supplies do no do well in the presence of a RF field. Does the STAX emit this type of interference through the power lead?

I would find it interesting that a supply of 1000ma would go into current shutdown. If you had a peak hold DMM or some other way to plot inrush current draw, it would be helpful to know what the device is actually drawing peak. If it is an over current situation, maybe you can get a NTC resistor to cut down the peak surge current. It might be a challenge to find one with that low of rating.

on the flip side, if its shutting down from not enough load, you need to put a small light bulb or such in parallel with the device for some additional start up load.

bob

If you would like, use a power PNP transistor on the (+) output and bias the base via the Hfe of the transistor to limit the max current of what the supply can handle. The Collector would then be the output and the Emitter to (+) of the power supply output. Base gets biased with appropriate R to maybe just below the max current of the supply.

The beta will shift upward a bit when the transistor gets warm but I don't think i'll matter after that..One could always place a Si diode on top of the transistor to help clamp the bias voltage at the base to stabilize it.

I've used simple PNP current limited circuits like that in many cases to fix inrush currents on small circuits.

You can do this with a NPN if you want to float the (-) from the collector.. Myself, I would go with the PNP..

"William Sommerwerck"

Current technology in audio power uses PWM amplification.

Switching frequencies are typically from 250 kHz up to over 1 MHz.

The A to Ds in most current audio uses sampling rates of 2.6 MHz.

Hi-fi FM radio is also audio - operates in the VHF range.

Radio microphones are considered part of "audio" too - frequencies used range from VHF up to several GHz.

.... Phil

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.

Who said this was a PWM amplifier?

The design dates back to 1996. It's highly unlikely the unit uses PWM -- why should it? The amp drives electrostatic earphones whose cross-sectional area is a bit larger than 1 square inch -- plus the cable capacitance. You don't need much current drive for that. What would be the advantage of PWM amplification?

Now, it might use a switching power supply to get the 580V DC needed for the polarizing voltage. But that's a different issue.

Thanks for the suggestion, but the amplifier is quite small, and I'm not going to rip into it for a modification of this sort.

What makes you think I take anything you say seriously? Or that I'm bothered that you so crudely disagree with anyone here, or am pleased when you do?

I couldn't care less. You are less than nothing, Mr. Allison.

"William Sommerwanker"

..... Phil

If you "Couldn't care less" why'd you post this?

Rheilly Phoull Inscribed thus:

I've seen a lot of laptop SM PSU simply cease to supply power to the load because the output caps have developed high ESR. Adding a suitable cap across the output often will confirm the problem.

My guess would be that the switcher is generating lots of hash, & it's upsetting the oscillator in the phones. Try looking at the DC with a 'scope.