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Inductor DC current rateing peak current

H

Hammy

Jan 1, 1970
0
I'm looking for a 390uH inductor for a Boost PFC choke 250W output
power.

After spending some time browsing data sheets,I'm confused why only
the DC current rating is shown. There is never any graph for current
vs inductance or inductance vs frequency or max peak current to avoid
saturation or graphs for core loss.

From looking at a data sheet on a Bourns vertical mount Toroid 560uH
@1kHz They specify at rated DC current an inductance drop from the
original 560uH to 314.18uH.



My PFC choke specifications at 65kHz are 4.9Apk and 3Arms would the
2321 560uH 3.6A one here be a possible candidate?

http://www.bourns.com/data/global/pdfs/2300_series.pdf


I could use a coilcraft part I have but its bigger then I would like
to use part C1062-BL

http://www.coilcraft.com/pdfs/c1061.pdf

Note the detailed specs compared to 99% of the other inductor
datasheets.
 
H

Hammy

Jan 1, 1970
0
Bill Sloman wrote
Inductance versus frequency is to some extent documented by the self-
resonance frequency of the inductor, which is usually given. You can
convert it to a parallel capacitance.

SRF is not given in the 1 page data sheet.
The Bourns parts are wound with a single layer of widely separated
turns of wire, for which the parallel capacitance usually comes out as
of the order of 1pF, which would put the lowest self-resonant
frequency around 5MHz and the highest closer to 50MHz

It could be that the losses due to induced currents in the core would
kill any such resonance, but pre-wound inductors are pretty much
always designed such that the self-resonance is tolerably sharp, so
that the inter-winding capacitance sets your upper frequency limit.

Commercial pre-wound indusctors are generally designed so that they
don't saturate below the DC current rating at the maximum rated
working temperature - which is usually set by the Curie temperature of
the core material.

I would hope it wouldnt satuarate below the DC limit or else the spec
would be useless.From what I recall any rateing DC or RMS current is
set by copper losses peak current is set by core material and size.A
massed produced inductor isnt going to use oversized cooper if the
core cant handle the energy.

They show a 43% drop in inductance at rated current. The core material
is'nt stated but I'm guessing it is'nt ferrite.
 
T

Tim Williams

Jan 1, 1970
0
Hammy said:
They show a 43% drop in inductance at rated current. The core material
is'nt stated but I'm guessing it is'nt ferrite.

If they have a color photo, you can guess the material type.
http://www.micrometals.com/materials_index.html
Mix 26 and 52 are quite popular, and fairly lossy (e.g., a typical DCM boost supply will have very little "dead time" ringing using these, whereas a ferrite core, with much lower losses, will ring significantly).

Tim
 
H

Hammy

Jan 1, 1970
0
If they have a color photo, you can guess the material type.
http://www.micrometals.com/materials_index.html
Mix 26 and 52 are quite popular, and fairly lossy (e.g., a typical DCM boost supply will have very little "dead time" ringing using these, whereas a ferrite core, with much lower losses, will ring significantly).

Tim

Well yes I guess I could , but should you really have too?
They are trying to sell a product so they should be providing the
information without someone having to jump through a bunch of hoops.


You would figure they would have more detailed specs on their site but
after browsing through the site and their catalogues they don't.

If I wanted to build 5k a year what do you have to do email some clown
in sales and ask for specifications that should already be included in
the data sheet.

I'm not just talking about the one inductor I posted about but the
majority of inductor data sheets,if they can even be called that only
state a dc current rating and maybe Q and srf.

I'm just going to use the coilcraft part at least I know what I can
expect.

Its for a NCP1654 "CCM" boost converter.
 
M

Martin Riddle

Jan 1, 1970
0
Hammy said:
Well yes I guess I could , but should you really have too?
They are trying to sell a product so they should be providing the
information without someone having to jump through a bunch of hoops.


You would figure they would have more detailed specs on their site but
after browsing through the site and their catalogues they don't.

If I wanted to build 5k a year what do you have to do email some clown
in sales and ask for specifications that should already be included in
the data sheet.

I'm not just talking about the one inductor I posted about but the
majority of inductor data sheets,if they can even be called that only
state a dc current rating and maybe Q and srf.

I'm just going to use the coilcraft part at least I know what I can
expect.

Its for a NCP1654 "CCM" boost converter.

Whats the lead time on that 1654? Mouser shows 4/18/2011

Coilcraft is good, easy samples. There are others
<http://www.interfacebus.com/inductors_transformers.html>

Check CWS www.coilws.com they might have something competitive .

I used the IRF1150, same CCM topology, the loop works well when setup
properly. But bypass Vcc well, and pick a mosfet with low input
capacitance.


Cheers
 
J

Joerg

Jan 1, 1970
0
Hammy said:
I'm looking for a 390uH inductor for a Boost PFC choke 250W output
power.

After spending some time browsing data sheets,I'm confused why only
the DC current rating is shown. There is never any graph for current
vs inductance or inductance vs frequency or max peak current to avoid
saturation or graphs for core loss.

There is but you have to politely ask. Sometimes they'll have to measure
it and they only do that if you dangle a BIG carrot in the form of a fat
potential purchase order.

Usually they state several values. For excample current for 30C or 40C
temp rise, then current for 20% inductance loss and 30% loss. That's
usually enough to design with. I wouldn't want to push an inductor much
past -30% in the peaks although some folks go to -50%. Probably the same
guys who won't shift before 6000rpm :)

From looking at a data sheet on a Bourns vertical mount Toroid 560uH
@1kHz They specify at rated DC current an inductance drop from the
original 560uH to 314.18uH.



My PFC choke specifications at 65kHz are 4.9Apk and 3Arms would the
2321 560uH 3.6A one here be a possible candidate?

http://www.bourns.com/data/global/pdfs/2300_series.pdf

44% drop at I-rated? Yikes! Personally I wouldn't like to push that one
to 4.9A peaks.
I could use a coilcraft part I have but its bigger then I would like
to use part C1062-BL

http://www.coilcraft.com/pdfs/c1061.pdf

Mucho mejor :)

Note the detailed specs compared to 99% of the other inductor
datasheets.


You should see some oriental IC datasheets ...
 
H

Hammy

Jan 1, 1970
0
There is but you have to politely ask. Sometimes they'll have to measure
it and they only do that if you dangle a BIG carrot in the form of a fat
potential purchase order.

Usually they state several values. For excample current for 30C or 40C
temp rise, then current for 20% inductance loss and 30% loss. That's
usually enough to design with. I wouldn't want to push an inductor much
past -30% in the peaks although some folks go to -50%. Probably the same
guys who won't shift before 6000rpm :)

Almost every Inductor datasheet I have looked at is 1 maybe two pages
one page consist of packaging information. The other page just states
DC current rateing DCR and maybe SRF.

Usually its for the whole series.What are they trying to save money on
paper?
44% drop at I-rated? Yikes! Personally I wouldn't like to push that one
to 4.9A peaks.

Yep thats what I figured. I'm useing the coilcraft part. I started the
layout I'm just waiting for the parts to come for the supply its
provideing the bus voltage for.
Mucho mejor :)

If they could only all be like that.
You should see some oriental IC datasheets ...

Dont get me started.;-)
 
J

Joerg

Jan 1, 1970
0
Hammy said:
Almost every Inductor datasheet I have looked at is 1 maybe two pages
one page consist of packaging information. The other page just states
DC current rateing DCR and maybe SRF.

There should always be at least one current for 20% or 30% or some other
percentage drop in inductance. Or an inductance given for the rated DC
current, like in one of the datasheets you posted.

Usually its for the whole series.What are they trying to save money on
paper?


They come from countries where there aren't many trees left?

But seriously, you can get more data, just not as a low volume user. For
example, I requested a specific additional datapoint on an inductor from
a Chinese manufacturer. They took it to the lab, ran tests and sent me
the actual plots. A lot more than I asked for.
 
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