3/8 ring core in 3F4

[Ken Smith]

Does anyone here know where I can get some toroids or other small cores in
3F4 material. I need about a 3/8 inch OD core.

I have a DC-DC that is working well but most of my losses are in core
losses. I need to fit into a very tight space. The height of the
finished inductor/transformer has to be under 0.3 inches.



--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hello Ken,

Does anyone here know where I can get some toroids or other small cores in
3F4 material. I need about a 3/8 inch OD core.

Check Kaschke K2003 material:
http://www.kaschke.de/
They have a rep in California (assuming you are in CA).

Or Magnetics "A".

I have a DC-DC that is working well but most of my losses are in core
losses. I need to fit into a very tight space. The height of the
finished inductor/transformer has to be under 0.3 inches.

Tried other materials such as #77 or J?

Regards, Joerg

http://www.analogconsultants.com

 

[John Popelish]

Ken Smith wrote:

Does anyone here know where I can get some toroids or other small cores in
3F4 material. I need about a 3/8 inch OD core.

I have a DC-DC that is working well but most of my losses are in core
losses. I need to fit into a very tight space. The height of the
finished inductor/transformer has to be under 0.3 inches.



I think that Fair Rite type 77 is superior to 3F4. Take a look at the

5977000201 toroid.
http://64.162.105.66/lspservices/xsinvfr.asp?PageNo=2&Mv=Page+Down
specs on page 137 of:
http://www.fair-rite.com/newfair/pdf/fr_catalog-14thed_rev3.pdf#page=1

 

[Ken Smith]

In article <sr7Oe.66$sV7.65@newssvr21.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[....]

Check Kaschke K2003 material:
http://www.kaschke.de/
They have a rep in California (assuming you are in CA).

Thanks for that lead.

Or Magnetics "A".
[...]
Tried other materials such as #77 or J?

Type 77 core material gets too lossy above about 100KHz. It isn't as good
as the 3F3 material I can easily get. I can easily give up a bit on the
Al number for the core, since my copper losses are quite low.

I'm switching at about 2MHz in this design.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <yLqdnZ24V6IugZTeRVn-rA@adelphia.com>,
John Popelish <jpopelish@rica.net> wrote:
[...]

I think that Fair Rite type 77 is superior to 3F4. Take a look at the
5977000201 toroid.

No, the numbers seem to say that type 77 is a bit worse at high
frequencies than the 3F3 material. Type 77 is not recomended above 100KHz.


--
--
kensmith@rahul.net forging knowledge

 

[John Popelish]

Ken Smith wrote:

In article <yLqdnZ24V6IugZTeRVn-rA@adelphia.com>,
John Popelish <jpopelish@rica.net> wrote:
[...]

I think that Fair Rite type 77 is superior to 3F4. Take a look at the
5977000201 toroid.


No, the numbers seem to say that type 77 is a bit worse at high
frequencies than the 3F3 material. Type 77 is not recomended above 100KHz.

I was just about to argue with you and I realized that I had misread
the frequency scale on the data sheet. Sorry.

 

[Ken Smith]

In article <86mdnSzrKb5Rr5TeRVn-2g@adelphia.com>,
John Popelish <jpopelish@rica.net> wrote:
[...]

I was just about to argue with you and I realized that I had misread
the frequency scale on the data sheet. Sorry.

Yes, it happens.

Thanks for confirming my, as it turns out, correct reading of charts.

If we could just get all the makers to use the same format, life would be
much easier.


--
--
kensmith@rahul.net forging knowledge

 

[amdxjunk]

If we could just get all the makers to use the >same format, life would be
much easier.

kensmith@rahul.net forging knowledge

Yes, Yes, I agree with that, and even different
formats in a single manufacturers catalog.
Mike

 

[Joerg]

Hello Ken,

I'm switching at about 2MHz in this design.

Wow. I am not sure 3F4 is right for that. Best would be to talk to an
engineer at one of the ferrite manufacturers about which material may be
best. I usually went to #43 when going into the MHz range but there is
some stuff in between as well, most likely more expensive though.

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <iKoOe.656$L77.359@newssvr19.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[...]

best. I usually went to #43 when going into the MHz range but there is

Thanks for pointing me back to the #43 material. It looks like I can get
it in toroids and the numbers on it look good.

The maker's suggested use for it is for EMI at frequencies over IIRC,
30MHz.

some stuff in between as well, most likely more expensive though.

Bah, cost is no object

--
--
kensmith@rahul.net forging knowledge

 

[legg]

On Sun, 21 Aug 2005 16:31:35 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

Does anyone here know where I can get some toroids or other small cores in
3F4 material. I need about a 3/8 inch OD core.

I have a DC-DC that is working well but most of my losses are in core
losses. I need to fit into a very tight space. The height of the
finished inductor/transformer has to be under 0.3 inches.

There aren't too many power inductor/transformer applications that
will unequivocally suit a toroidal ferrite core - a small gap is often
beneficial.

Although cost may be no object, availability generally dictates the
use of parts commonly used elswhere.

`3/8 OD toroids are metric T8 orT10 (TDK), R9.5 or R10 (EPCOS), TN9 or
TN9.5 (Ferroxcube).

Low profile bobbin and core assemblies (eg ER14.5) are available from
EPCOS, TDK and others in low loss material, gapped or not.

How have you established that core losses are dominant (zero load
rises)? Can you reverse this imbalance, to prove it?

Tolerance of core loss in production of larger parts generally
prevents you from allowing it any sign of dominance in a prototype -
it can easily double. In a smaller part, the responsibility for heat
removal is likely shared by the total assembly - it's harder to
pinpoint. This can even be useful.

RL

 

[Ken Smith]

In article <u9dlg110ihphfgj45ihjrdebctqah3d2ig@4ax.com>,
legg <legg@nospam.magma.ca> wrote:
[...]

There aren't too many power inductor/transformer applications that
will unequivocally suit a toroidal ferrite core - a small gap is often
beneficial.

Yes, in general, the core used in a DC-DC converter is normally gapped in
some way. Toroids can have a "distributed gap" where the magnetic
material is mixed with some non-magnetic material to provide the gapping.
In my case, the availability of the part off the shelf is driving the
selection of the core. If the core was optimized, it could be quite a bit
smaller.

[...]

How have you established that core losses are dominant (zero load
rises)? Can you reverse this imbalance, to prove it?

The design is basically a SEPIC converter and an isolated CUK converter
sharing a core to make two outputs. As a result, I can't use the no-load
losses method to do an in application measurement.

I this situation the measurement is made by measuring the temperature rise
of the copper and the core in the circuit and then reproducing the rise
out of the circuit. Because the inductor is in a confined space, it
doesn't take much power to cause the rise I'm seeing. My best estimate is
that just about 0.3W is being lost in the inductor when I'm making 3W of
output power. The semiconductors losses are about another 0.3W.



--
--
kensmith@rahul.net forging knowledge

 

[Harry Dellamano]

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:defbk5$eb1$1@blue.rahul.net...

The design is basically a SEPIC converter and an isolated CUK converter
sharing a core to make two outputs. As a result, I can't use the no-load
losses method to do an in application measurement.

Ok Ken, you got my attention. Let's see this SEPIC + CUK sharing one core.

Sounds interesting. Can you post a schematic or sketch?
Harry

 

[Joerg]

Hello Ken,

Thanks for pointing me back to the #43 material. It looks like I can get
it in toroids and the numbers on it look good.

And it's dirt cheap. The variety is larger than that of the beer aisle
at Safeway.

The maker's suggested use for it is for EMI at frequencies over IIRC,
30MHz.

I have used #43 material for pulse transformers in the several 10nsec
range. Also for EMI. The FT-37-43 core is 0.375" OD and 0.125" high. If
that saturates in your application you could stack two for experiments.

some stuff in between as well, most likely more expensive though.

Bah, cost is no object

Our tax Dollars at work? Lucky you. My toroid inductors often have to
come in under 50c, custom wound and all. But that is in huge quantities.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello Ken,

The design is basically a SEPIC converter and an isolated CUK converter
sharing a core to make two outputs. As a result, I can't use the no-load
losses method to do an in application measurement.

Converters like the SEPIC generally do not need gapped cores. Also, as
Harry pointed out, in a SEPIC you can "core share" (ain't that a nice
word?) and wind both inductors on the same core.

I this situation the measurement is made by measuring the temperature rise
of the copper and the core in the circuit and then reproducing the rise
out of the circuit. Because the inductor is in a confined space, it
doesn't take much power to cause the rise I'm seeing. My best estimate is
that just about 0.3W is being lost in the inductor when I'm making 3W of
output power. The semiconductors losses are about another 0.3W.

0.3W core loss in a 3W converter is huge. Typically core loss would
contribute a percent or so, if that. The thing to watch out for is
saturation at the end of the charge cycle. If it isn't a current mode
concept you are using install a very small resistor in the source leg of
the FET. 100milliOhms or so, something a current mode concept already
has. Look at it with a scope. You should ideally see a nice linear ramp.
If you see a marked rise at the end, like a shark fin, then saturation
is setting in. This is also a reason why continuous mode may not be such
a good thing when the core is on the skimpy side.

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <NjKOe.368$sV7.40@newssvr21.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[...]

I have used #43 material for pulse transformers in the several 10nsec
range. Also for EMI. The FT-37-43 core is 0.375" OD and 0.125" high. If
that saturates in your application you could stack two for experiments.

I went to the store that doesn't have beer and chips mixed in with the
sockets and chips[1], and, *bummer*, They are out of them. I will have to
order some. I meant to do the order today but I got busy putting the
prototype in a box and then trapped in a meeting.


[1] ie: it isn't Fry's

Our tax Dollars at work? Lucky you. My toroid inductors often have to
come in under 50c, custom wound and all. But that is in huge quantities.

Right now, this is privately funded. The product will sell for about the
same as a new car so a few bucks on a core won't matter.

I have a $300 OCXO, a $100 CPLD and a couple of $50 micros so most other
things get lost into the noise.



--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <yNGOe.4903$Vg7.3165@trnddc06>,
Harry Dellamano <harryd@tdsystems.org> wrote:
[...]

Ok Ken, you got my attention. Let's see this SEPIC + CUK sharing one core.
Sounds interesting. Can you post a schematic or sketch?
Harry

Here's the basic idea:

C1 D1
--[L1]--[L2A]-+-----!!----+----->!--+----- Vout1
! ! !
!- [L2B] --- C2
! ! ---
!- GND !
! GND
GND


C3
---!!--+----[L2D]-[L3]-+-- Vout2
! ! !
! --- D2 ---
[L2C] ^ --- C4
! ! !
-------+---------------+--


L2 has lots of winding on it and is custom. L1 and L3 are small off the
shelf parts.

The input and the Vout2 have low ripple. Vout1 is the one used for the
real feedback. Vout2 is only semi regulated.

I'm thinking of dropping the Vout2 back to just being isolated flyback.
--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <EsKOe.519$dw4.56@newssvr29.news.prodigy.net>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:

The thing to watch out for is
saturation at the end of the charge cycle.

The numbers say that I'm only at about 1/4 saturation. I'm at home and
the real numbers are at work but that much I rememeber. This is why I
decided it was just the core material that was at fault.

If it isn't a current mode
concept you are using install a very small resistor in the source leg of
the FET.

It is a current mose design.

This is sort of what the current does.

.................*........
...............*..*.......
.............*....*.......
...........*......*.......
.........*........*.......
.....*..*.........*.......
.....***..........*.......
.....**...........*.......
.....*............*.......
****.............********
..................*.......

The slight decreasing slope may be from the way I did the measurement or
the coupling capacitor being a bit too small.

I see some ringing on the edges of the switching.

--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hello Ken,

In article <NjKOe.368$sV7.40@newssvr21.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[...]

I have used #43 material for pulse transformers in the several 10nsec
range. Also for EMI. The FT-37-43 core is 0.375" OD and 0.125" high. If
that saturates in your application you could stack two for experiments.


I went to the store that doesn't have beer and chips mixed in with the
sockets and chips[1], and, *bummer*, They are out of them. I will have to
order some. I meant to do the order today but I got busy putting the
prototype in a box and then trapped in a meeting.

Some of the larger Radio Shacks used to have 43 cores. But not these
flat versions.

Amidon is pretty good if you need a few cores quickly.

ie: it isn't Fry's

I would be surprised if they had ferrite toroids.

Our tax Dollars at work? Lucky you. My toroid inductors often have to
come in under 50c, custom wound and all. But that is in huge quantities.

Right now, this is privately funded. The product will sell for about the
same as a new car so a few bucks on a core won't matter.

I have a $300 OCXO, a $100 CPLD and a couple of $50 micros so most other
things get lost into the noise.

Wow. Guess a 50c ferrite pales in comparison.

Regards, Joerg

http://www.analogconsultants.com