Toroid Core for LED V Boost

[Watson A.Name - \Watt Sun, the Dark Remover\]

The toroid cores that I've been using for the V boost circuits I've
built are similar to this one. I think mine may be a slight bit larger.
They are commonly used on mouse and keyboard cables as RFI suppressors.

http://www.mpja.com/productview.asp?product=12406+FL


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[Jim Thompson]

Voltage boost regulators store energy in the magnetic field of the
inductor first, and dump it to the load second. Ungapped ferrite
cores are not so efficient in this mode, since the core absorbs a
significant fraction of the energy stored, each cycle. Cores with a
small air gap store most of their magnetic energy in the gap, which
absorbs no energy. You might do a comparative experiment with a core
you have fractured and glued back together. This produces a few small
gaps distributed around the toroid. It will lower the Al value of the
core, so more turns will be needed to achieve the same inductance, but
you may find that the overall efficiency rises.

Back in my SMPS phase, 1977-1987, I was fond of gapped pot cores...
easy-to-wind split bobbins, nice clip mounts.

...Jim Thompson

 

[John Popelish]

The toroid cores that I've been using for the V boost circuits I've
built are similar to this one. I think mine may be a slight bit larger.
They are commonly used on mouse and keyboard cables as RFI suppressors.

http://www.mpja.com/productview.asp?product=12406+FL

Voltage boost regulators store energy in the magnetic field of the
inductor first, and dump it to the load second. Ungapped ferrite
cores are not so efficient in this mode, since the core absorbs a
significant fraction of the energy stored, each cycle. Cores with a
small air gap store most of their magnetic energy in the gap, which
absorbs no energy. You might do a comparative experiment with a core
you have fractured and glued back together. This produces a few small
gaps distributed around the toroid. It will lower the Al value of the
core, so more turns will be needed to achieve the same inductance, but
you may find that the overall efficiency rises.

 

[Michael]

The toroid cores that I've been using for the V boost circuits I've
built are similar to this one. I think mine may be a slight bit larger.
They are commonly used on mouse and keyboard cables as RFI suppressors.

http://www.mpja.com/productview.asp?product=12406+FL

The ones I use were pulled from a couple PC power supplies. Two of theses are
identical, 5/8" O.D. x 1/8" high with 3/8" I.D, are shaped like miniature bagels
(i.e. have no sharp corners), and have a rough surface. Have to be careful not
to abrade the wire enamel while winding.

One (as yet used) is smaller, 3/8" I.D. x 1/8" high with 3/16" I.D., with smooth
surface and sharp corners.

One very nice toroid, about the same dimensions as above, is completely coated
with a smooth white material, some kind of plastic or epoxy. I used it in the
first booster I ever built (several days ago). It can use more turns, so I'll
strip it and rewind sometime.


Enameled wire - about 20AWG - was stripped off small transformers from the same
PC power supplies.

My latest booster design uses one of the rough-surface toroids (above) and the
20# wire. I put a new AA in it at 3:30 PM on Friday afternoon and it's still
running as I write this (12:21 PM), nearly 45 hours. The All Electronics bright
white LED is dim now compared to its dazzling self when the battery was fresh,
but the light is sufficient that it could be used for close-in (12" or so)
work. Transistor is a "wimpy 2N3904". 1K base resistor.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Voltage boost regulators store energy in the magnetic field of the
inductor first, and dump it to the load second. Ungapped ferrite
cores are not so efficient in this mode, since the core absorbs a
significant fraction of the energy stored, each cycle. Cores with a
small air gap store most of their magnetic energy in the gap, which
absorbs no energy. You might do a comparative experiment with a core
you have fractured and glued back together. This produces a few small
gaps distributed around the toroid. It will lower the Al value of the
core, so more turns will be needed to achieve the same inductance, but
you may find that the overall efficiency rises.

The literature I've read on ferrites state that the ferrite particles
are suspended in a glasslike compound that acts like distributed gaps.
It's doubtful that your suggestion would help.

 

[John Popelish]

The literature I've read on ferrites state that the ferrite particles
are suspended in a glasslike compound that acts like distributed gaps.
It's doubtful that your suggestion would help.

I think you are confusing ferrites (a poly crystalline spinel) with
powdered iron cores. The latter contain many individual iron
particles suspended in a binder and those do have thousands of tiny
gaps distributed all around the core. The Al value of a high
permeability ferrite core takes a big jump down with the addition of a
tiny gap, indicating that there are no other significant gaps in their
structure.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

The ones I use were pulled from a couple PC power supplies. Two of theses are
identical, 5/8" O.D. x 1/8" high with 3/8" I.D, are shaped like miniature bagels
(i.e. have no sharp corners), and have a rough surface. Have to be careful not
to abrade the wire enamel while winding.

One (as yet used) is smaller, 3/8" I.D. x 1/8" high with 3/16" I.D., with smooth
surface and sharp corners.

One very nice toroid, about the same dimensions as above, is completely coated
with a smooth white material, some kind of plastic or epoxy. I used it in the
first booster I ever built (several days ago). It can use more turns, so I'll
strip it and rewind sometime.


Enameled wire - about 20AWG - was stripped off small transformers from the same
PC power supplies.

My latest booster design uses one of the rough-surface toroids (above) and the
20# wire. I put a new AA in it at 3:30 PM on Friday afternoon and it's still
running as I write this (12:21 PM), nearly 45 hours. The All Electronics bright
white LED is dim now compared to its dazzling self when the battery was fresh,
but the light is sufficient that it could be used for close-in (12" or so)
work. Transistor is a "wimpy 2N3904". 1K base resistor.

You didn't say what the total current was from a fresh AA cell. I put a
transistor socket on one of my circuits. I found that with the 2N3904 I
get about 20 to 40mA total, sometimes it goes up a bit because the
transistor is getting warmer (not so good, expecially if it's a hot
day). With the 2N4402, roughly double that, 50 to 80mA, and it doesn't
get warm. With the BC337 or BC338 I get 70 to 100mA total current,
sometimes a bit more. With the ZTX650, 2SD965, NTE11, etc., total
current will go up dramatically, sometimes 200mA, so it really needs to
have two or more LEDs. If you check the datasheets, say, from
Fairchild, the 2N4401 has roughly twice the chip area as the 2N3904.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I think you are confusing ferrites (a poly crystalline spinel) with
powdered iron cores. The latter contain many individual iron
particles suspended in a binder and those do have thousands of tiny
gaps distributed all around the core. The Al value of a high
permeability ferrite core takes a big jump down with the addition of a
tiny gap, indicating that there are no other significant gaps in their
structure.

They talk about both distributed air gaps and gapped ferrites here.
http://powerelectronics.com/mag/power_inductor_core_technology_2/

They also say, "Gap loss can drastically increase core losses due to
fringing flux around the air gap. The fringing flux can intersect the
copper windings, creating excessive eddy currents in the wire. Also, hot
spots on the core can develop as flux crowds near the air gap."

I really don't think I could break a toroid into two clean halves; from
my experience sawing them they would fracture into several larger pieces
and some smaller crumbs. I don't think I want to have to glue all those
back together.

 

[John Popelish]

They talk about both distributed air gaps

in powdered metal cores...

and gapped ferrites here.

http://powerelectronics.com/mag/power_inductor_core_technology_2/

They also say, "Gap loss can drastically increase core losses due to
fringing flux around the air gap. The fringing flux can intersect the
copper windings, creating excessive eddy currents in the wire. Also, hot
spots on the core can develop as flux crowds near the air gap."

The key word is "can" as in extreme cases. At your flux and power
levels and with the tiny gaps I have been talking about (a thousandth
of an inch of glue) these are not at all a problem.

I really don't think I could break a toroid into two clean halves; from
my experience sawing them they would fracture into several larger pieces
and some smaller crumbs. I don't think I want to have to glue all those
back together.

I have made small gapped toroids by lining a vise with a bit of
cardboard and gently squeezing the toroid across the diameter till it
fractured into 4 quadrants. The trick is to glue them back together
in their original positions, so they fit well. Not a practical
production technique, but makes for an interesting comparative
experiment.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

in powdered metal cores...

and gapped ferrites here.


The key word is "can" as in extreme cases. At your flux and power
levels and with the tiny gaps I have been talking about (a thousandth
of an inch of glue) these are not at all a problem.


I have made small gapped toroids by lining a vise with a bit of
cardboard and gently squeezing the toroid across the diameter till it
fractured into 4 quadrants. The trick is to glue them back together
in their original positions, so they fit well. Not a practical
production technique, but makes for an interesting comparative
experiment.

Well, now that you own up to experimenting with this, what,
quantitatively, was the result? If we're going to go busting skulls,
I'd like to see the results before I decide to get invoived. Give us
some before and after figures to get an idea of what the benefits and
drawbacks are. After all, I've glued my fingers to stuff with CA crazy
glue a few times and I don't particularly like peeling off a layer of
skin every time. ;-)

 

[John Popelish]

Well, now that you own up to experimenting with this, what,
quantitatively, was the result? If we're going to go busting skulls,
I'd like to see the results before I decide to get invoived. Give us
some before and after figures to get an idea of what the benefits and
drawbacks are. After all, I've glued my fingers to stuff with CA crazy
glue a few times and I don't particularly like peeling off a layer of
skin every time. ;-)

It's been a few years, and I was playing with some boost converter
designs. All I remember is that before I broke and glued the cores (I
used 5 minute epoxy, not instant glue, with a rubber band around the
toroid, cleaned up with sand paper, after ward) they were saturating
and killing the efficiency. There was a big spike of current in the
charge phase that did little for the dump phase. After being gapped,
(I had to approximately double the number of turns to get the same
inductance) the current rose much more linearly during the charge
phase and ramped down more linearly during the dump phase and the
overall efficiency improved quite measurably, in spite of the higher
copper losses (which were a tiny part of the total losses). If you
want to compare apples to cracked and glued apples, you need to make
two inductors with the same core and the same inductance (one gapped
and one ungapped) and make comparative measurements with them plugged
into the same circuit.

I don't want to spoil all your fun.

 

[Michael]

You didn't say what the total current was from a fresh AA cell. I put a
transistor socket on one of my circuits. I found that with the 2N3904 I
get about 20 to 40mA total, sometimes it goes up a bit because the
transistor is getting warmer (not so good, expecially if it's a hot
day). With the 2N4402, roughly double that, 50 to 80mA, and it doesn't
get warm. With the BC337 or BC338 I get 70 to 100mA total current,
sometimes a bit more. With the ZTX650, 2SD965, NTE11, etc., total
current will go up dramatically, sometimes 200mA, so it really needs to
have two or more LEDs. If you check the datasheets, say, from
Fairchild, the 2N4401 has roughly twice the chip area as the 2N3904.

DVM read 45ma. Couldn't measure any of the real nitty-gritty because my o'scope
is ... er ... resting.

Yeah, I agree that the 2N3904 is contarindicated for this app. but there's
nothing better in theparts bins. Ya gotta understand that most of my
semiconductor stash dates from my A.F. days (late 60's) and tecnician days
(early 70's).

I checked out a couple photo shops, hoping to get my hands on some disposable
camera flash guts as you(?) suggested, and was told at both places that they
don't toss disposables. They turn 'em in for cash. Ah well ...... some Zetex
goodies will be coming soon.

 

[Michael]

It's been a few years, and I was playing with some boost converter
designs. All I remember is that before I broke and glued the cores (I
used 5 minute epoxy, not instant glue, with a rubber band around the
toroid, cleaned up with sand paper, after ward) they were saturating
and killing the efficiency. There was a big spike of current in the
charge phase that did little for the dump phase. After being gapped,
(I had to approximately double the number of turns to get the same
inductance) the current rose much more linearly during the charge
phase and ramped down more linearly during the dump phase and the
overall efficiency improved quite measurably, in spite of the higher
copper losses (which were a tiny part of the total losses). If you
want to compare apples to cracked and glued apples, you need to make
two inductors with the same core and the same inductance (one gapped
and one ungapped) and make comparative measurements with them plugged
into the same circuit.

I don't want to spoil all your fun.

--

This discussion has picqued my interest. I gotta fidn some more "donuts" and
have at it.

 

[John Popelish]

This discussion has picqued my interest. I gotta fidn some more "donuts" and
have at it.

Excellent! If you have trouble finding similar pairs, let me know and
I will mail you a few.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

DVM read 45ma. Couldn't measure any of the real nitty-gritty because my o'scope
is ... er ... resting.

Yeah, I agree that the 2N3904 is contarindicated for this app. but there's
nothing better in theparts bins. Ya gotta understand that most of my
semiconductor stash dates from my A.F. days (late 60's) and tecnician days
(early 70's).

Get some transistors on Ebay, for a few dollars including shipping.

I checked out a couple photo shops, hoping to get my hands on some disposable
camera flash guts as you(?) suggested, and was told at both places that they
don't toss disposables. They turn 'em in for cash. Ah well ...... some Zetex
goodies will be coming soon.

Zetex transistors are overpricesd if you buy them from a distrib. The
turkeys turn the disposables back in and they refill them and resell
them as new. Dirty, steenkin' rats.

Try Rite Aid, Sav-on, Albertson's or other such drugstores, amaybe even
Walgreen's. I opened one up recently and found a 2SD2470, which looks
suspiciously like a ZTX650 - same tiny case.

 

[Michael]

Excellent! If you have trouble finding similar pairs, let me know and
I will mail you a few.

Tnx, John.

 

[Michael]

Get some transistors on Ebay, for a few dollars including shipping.


Zetex transistors are overpricesd if you buy them from a distrib. The
turkeys turn the disposables back in and they refill them and resell
them as new. Dirty, steenkin' rats.

Hard on you and me but easy on the environment. I wouldn't complain very loudly
about "refilling" because I'm a dyed-in-the-wool dumpster diver.

Try Rite Aid, Sav-on, Albertson's or other such drugstores, amaybe even
Walgreen's. I opened one up recently and found a 2SD2470, which looks
suspiciously like a ZTX650 - same tiny case.

Tnx for the heads-up. I think we do have a Rite Aid around here (across from
Rat Shack, coincidently). Forgot all about that drug store. It's a mile from
where I live, while CVS is just around the corner from me.

 

[John Popelish]

John Popelish wrote:

Tnx, John.

No problem. It is my hobby to collect cores, so I have a pile of
them. Just email me with your address.

Another way to do this experiment is to get one of those split beads
that have a plastic shell that snaps it around a cable. You can place
various paper shims between the core halves and produce various gapped
configurations. The only problem is that these cores are so big that
you have to scale the whole circuit way up ot get meaningful results,
and there is no way to get the reference ungapped configuration,
because the core cut surfaces are not polished, so even a no paper
example has some effective gap.

 

[Michael]

Just passed the 69-hour point and that sucker is still going, though markedly
dimmer than yesterday at this time. I can read 6-point Courier (with some
difficulty) with page about 1 foot away from LED.

 

[Fred Art]

Michael <[email protected]> while reading the NewsGroups, express out
opinion in

I checked out a couple photo shops, hoping to get my hands on
some disposable camera flash guts as you(?) suggested, and was
told at both places that they don't toss disposables. They turn
'em in for cash. Ah well ...... some Zetex goodies will be
coming soon.

Check out Ebay stuff like this is available.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&rd=1&item=7501877040
&ssPageName=STRK:MESE:IT

F.Art