Electronics > Beginners

When are SMPS not used these days?

<< < (4/5) > >>

exe:

--- Quote from: Siwastaja on June 23, 2019, 08:37:25 pm ---some modern regulators regulate at MHz or tens of MHz ranges just fine

--- End quote ---

Do you have a few part numbers as example?

Doctorandus_P:
MP1584 runs at 1.5MHz and indeed it is not an exceptional high frequency.
LT8650 runs at 2MHz.

2 unrelated links about "silent switcher".
https://www.mouser.com/pdfdocs/ACTSilentSwitcher.pdf
https://linearaudio.nl/silentswitcher

The first link is from a presentation from Analog Devices.
It combines extremely good PCB layout with on chip features that make the loop area (and thus stray magnetic fields) of the "hot" components very small. Syncrhonous switching also eliminates external diodes, which eliminate ringing and again, also results in still smaller loop area.

Also:
A long time ago I had an old 400MHz analog scope, with a big bundle of twinax as a delay line wound around the CRT.
It was quite a beast.

It had 2 SMPS boards moulded in some half hard epoxy / rubbery compound, and when they failed I replaced them with 2 toroidal transformers.
After that the traces on the CRT were all wobbly because of the stray magnetic field of those transformers. Even though the transformers were in a separately shielded compartment ( More than 1mm thick aluminum between the transformers and the CRT's).

ejeffrey:

--- Quote from: Doctorandus_P on June 25, 2019, 04:48:56 pm ---After that the traces on the CRT were all wobbly because of the stray magnetic field of those transformers. Even though the transformers were in a separately shielded compartment ( More than 1mm thick aluminum between the transformers and the CRT's).

--- End quote ---

Of course.  Aluminum hardly shields low frequency magnetic fields at all.  You would need a few cm thick plate to do much of anything.  Or: a thin layer of steel or mu-metal or both.

exe:

--- Quote from: Doctorandus_P on June 25, 2019, 04:48:56 pm ---MP1584 runs at 1.5MHz and indeed it is not an exceptional high frequency.
LT8650 runs at 2MHz.

--- End quote ---

Oh, I thought we are talking about linear regulators with bandwidth beyond megaherz... I'm not sure that high frequency helps. I'd say the opposite, as it requires sharper edges to achieve same efficiency. Although, smaller frequency would require bigger components, which in turn creates more parasitics....

Frankly, I'm yet to build a switcher myself, but I saw other people doing it :). Harmonics can go well into 500MHz+, filtering such frequencies is difficult. Even probing is a challenge, a typical scope with passive probes cannot do that. So, I'm a bit skeptical hearing that "filtering is not a problem", etc. I don't buy this :).

I think the reason smps everywhere, including point-of-load, is that most circuits are not that sensitive to broadband noise. They also often use post-regulator. But post-regulators have just so much bandwidth, much less than most people think. I'd say even more, most regulators don't do anything beyond a few hundreds of kHz, all the high-freq filtering/PSRR is solely due to input/output caps... Except, may be some special rf regulators. Although, I just picked one I have, rt9193, and PSRR is not so good.

Anyway, please post part numbers/circuits with low noise, I'm happy to dive deeper into the subject.

PS as of noise from a toroidal tranny, I don't think it's an issue. I can imagine why CRT is sensitive to it, but most circuits are not. Even if there is induced noise, it's just 50/60Hz. My DIY power supply I built has a very good performance despite unshielded tranny. Well below 1mV of noise (limits of my oscilloscope sensitivity), thanks to lt3080. I actually don't have tools to measure its noise. May be I'll build a noise amplifier one day...

james_s:
I still see linear supplies in things like microwave ovens and the occasional LED clock radio although those are less common all the time. When you want a high reliability device that will run for a decade or more, a linear supply is cheaper than an equivalently reliable switcher. They are also nice in radio gear because they tend to be quieter from an RF standpoint. Yes it's possible to make a very quiet switcher but you'll usually eat up your cost savings in doing so.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod