Finding sufficiently crappy inductors

Should be okay with a soft start, no? The inrush isn't very serious on a 3V rail.

I tried it with four 10 uF tants and a 1-ohm series resistor, and it didn't fix it. :(

Cheers

Phil Hobbs

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Phil Hobbs
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I use 35v tants on the outputs of 317 and 1117 type regs, 3.3 and 5 volts, sometimes 12, and they seem fine. The ESR is just right for those regs, even with a lot of ceramic bypasses all over the place.

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John Larkin

Yeah, that's why I changed it, to putting a transformer in series with the undamped inductor. Unlike a pi filter with a resistor, there's no DC drop to contend with, which could be important if the necessary resistance is high.

Reply to
whit3rd

Divided? I thought you /wanted/ low Q!

Tim

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Reply to
Tim Williams

yeah, but not zero :)

NT

Reply to
tabbypurr

Q goes to 1 at high frequencies, because skin effect is diffusive. :)

Tim

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Tim Williams

add a network at the PS and loop output but before the filter..

the network consists of R in series with C to ground. this will D Q the load with no impact on the post filter. maybe you need R C __and L__in series.

series resonate at the freq it wants to oscillate adjust the R as required.

m
Reply to
makolber

Hi,

What would your switchers do if you use an IC to create a spread spectrum clock from the 2.15MHz? That could have the effect of cancelling a lot of the output filter feedback resonance maybe.

cheers, Jamie

Reply to
Jamie M

Hi,

Another idea, what about reducing the feedback loop frequency response of the switchers and then adding electrolytic capacitors after the PI filter, near the loads. If the loads current ripple isn't too high it shouldn't need to be compensated for by the switcher anyway, and the PI can manage it.

cheers, Jamie

Reply to
Jamie M

I misunderstood your second post. That might well work, if I can (a) find such a part, and (b) fit it into the design.

Thanks

Phil Hobbs

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Reply to
Phil Hobbs

I do. But shorted-turn effects greatly reduce inductance, which I don't want.

Cheers

Phil Hobbs

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Phil Hobbs

Hi,

I think using SEPIC converters in place of the buck and boost converters could also solve the issue, as they could push/pull their output to keep it regulated.

cheers, Jamie

Reply to
Jamie M

f

I must have hopelessly misunderstood what you want, it sounds as if you wan t cores that work great at some unknown hf, perhaps 2MHz, but lose all q at 150kHz.

Wire rope, even if each strand were insulated, which stainless steel is, wo uld surely have no prospect of doing that. But I can think of something tha t just might.

NT

Reply to
tabbypurr

Putting an L-R network in parallel with the L is good for damping input fil ters. I don't see why it wouldn't work for a buck output stage as well. A nd the damping L is smaller than the original L, as opposed to using a damp ing C larger than the original C.

I always reference this paper for picking the value of R:

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Reply to
sea moss

Well, it's best to start from what you really want and work down to what you can get. ;) Whit's transformer-coupled resistor would be a good fit if I could afford the space. (The usual thing.)

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Thanks. In this case the output filter resonance is destabilizing the FB loop--there's no significant frequency component of the load current that's up above 1 kHz. I'll have a squint at the paper though.

Cheers

Phil Hobbs

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Phil Hobbs

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't

want cores that work great at some unknown hf, perhaps 2MHz, but lose all q at 150kHz.

, would surely have no prospect of doing that. But I can think of something that just might.

A wire with ferrite beads on behaves as you want at dc & 150kHz. A small ca p across it could let hf through.

NT

Reply to
tabbypurr

Ferrite is pretty good at 150 kHz. Where would the loss come from?

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

yes :) I meant whatever inductor suits your 150kHz purpose.

NT

Reply to
tabbypurr

That's the one I'm trying to find. Works great at 2 MHz. ;)

Cheers

Phil Hobbs

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Phil Hobbs

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