Electronics Forums > calculating number of turns on a transformer

# calculating number of turns on a transformer

Jamie Morken
Guest
Posts: n/a

 10-24-2007, 10:43 PM
Hi,

I have a flyback transformer design in ltspice with a 1mH primary coil,
I would like to see how many turns this would require on this transformer:

core size: E375

falco part#: 1831-331-002

cross section area Ac(cm^2) =0.840

magnetic path length (cm) = 6.94

WaAc(cm^4) = 0.856

core volume(cm^3) = 5.830

Is there a formula to calculate the required number of primary
turns to get about 1mH inductance from this data? Thanks for
any help.

cheers,
Jamie

Jamie Morken
Guest
Posts: n/a

 10-24-2007, 10:46 PM
Jamie Morken wrote:
> Hi,
>
> I have a flyback transformer design in ltspice with a 1mH primary coil,
> I would like to see how many turns this would require on this transformer:
>
> core size: E375
>
> falco part#: 1831-331-002
>
> cross section area Ac(cm^2) =0.840
>
> magnetic path length (cm) = 6.94
>
> WaAc(cm^4) = 0.856
>
> core volume(cm^3) = 5.830
>
>
>
> Is there a formula to calculate the required number of primary
> turns to get about 1mH inductance from this data? Thanks for
> any help.
>
> cheers,
> Jamie

I know the flyback configuration will decrease the inductance
too, I guess this makes it harder..

Tam/WB2TT
Guest
Posts: n/a

 10-25-2007, 12:19 AM

"Jamie Morken" <(E-Mail Removed)> wrote in message
news:%TPTi.139170\$Da.65705@pd7urf1no...
> Hi,
>
> I have a flyback transformer design in ltspice with a 1mH primary coil,
> I would like to see how many turns this would require on this transformer:
>
> core size: E375
>
> falco part#: 1831-331-002
>
> cross section area Ac(cm^2) =0.840
>
> magnetic path length (cm) = 6.94
>
> WaAc(cm^4) = 0.856
>
> core volume(cm^3) = 5.830
>
>
>
> Is there a formula to calculate the required number of primary
> turns to get about 1mH inductance from this data? Thanks for
> any help.
>
> cheers,
> Jamie

They can boil all this information down into one constant, sometimes called
Al, given in uH/100 turns. You might want to see if they publesh that for

Tam

Eeyore
Guest
Posts: n/a

 10-25-2007, 02:13 PM

Jamie Morken wrote:

> Hi,
>
> I have a flyback transformer design in ltspice with a 1mH primary coil,
> I would like to see how many turns this would require on this transformer:
>
> core size: E375
>
> falco part#: 1831-331-002
>
> cross section area Ac(cm^2) =0.840
>
> magnetic path length (cm) = 6.94
>
> WaAc(cm^4) = 0.856
>
> core volume(cm^3) = 5.830
>
>
> Is there a formula to calculate the required number of primary
> turns to get about 1mH inductance from this data? Thanks for
> any help.

I suggest you get a copy of Epcos's Ferrite Magnetic Designer program.

Graham

John Larkin
Guest
Posts: n/a

 10-25-2007, 02:26 PM
On Wed, 24 Oct 2007 22:43:07 GMT, Jamie Morken <(E-Mail Removed)>
wrote:

>Hi,
>
>I have a flyback transformer design in ltspice with a 1mH primary coil,
>I would like to see how many turns this would require on this transformer:
>
>core size: E375
>
>falco part#: 1831-331-002
>
>cross section area Ac(cm^2) =0.840
>
>magnetic path length (cm) = 6.94
>
>WaAc(cm^4) = 0.856
>
>core volume(cm^3) = 5.830
>
>
>
>Is there a formula to calculate the required number of primary
>turns to get about 1mH inductance from this data? Thanks for
>any help.
>
>cheers,
>Jamie

Call them and ask what's the Al value. It's amazing that many
magnetics suppliers don't furnish this. They could also furnish a
number of other handy electrical and thermal values that are a
nuisance to calculate, like gauss per ampere-turn and temperature rise
per watt.

John

Jamie Morken
Guest
Posts: n/a

 10-26-2007, 08:55 AM
Eeyore wrote:
>
> Jamie Morken wrote:
>
>> Hi,
>>
>> I have a flyback transformer design in ltspice with a 1mH primary coil,
>> I would like to see how many turns this would require on this transformer:
>>
>> core size: E375
>>
>> falco part#: 1831-331-002
>>
>> cross section area Ac(cm^2) =0.840
>>
>> magnetic path length (cm) = 6.94
>>
>> WaAc(cm^4) = 0.856
>>
>> core volume(cm^3) = 5.830
>>
>>
>> Is there a formula to calculate the required number of primary
>> turns to get about 1mH inductance from this data? Thanks for
>> any help.

>
> I suggest you get a copy of Epcos's Ferrite Magnetic Designer program.

cheers,
Jamie

>
> Graham
>

Jamie Morken
Guest
Posts: n/a

 10-26-2007, 08:56 AM
John Larkin wrote:
> On Wed, 24 Oct 2007 22:43:07 GMT, Jamie Morken <(E-Mail Removed)>
> wrote:
>
>> Hi,
>>
>> I have a flyback transformer design in ltspice with a 1mH primary coil,
>> I would like to see how many turns this would require on this transformer:
>>
>> core size: E375
>>
>> falco part#: 1831-331-002
>>
>> cross section area Ac(cm^2) =0.840
>>
>> magnetic path length (cm) = 6.94
>>
>> WaAc(cm^4) = 0.856
>>
>> core volume(cm^3) = 5.830
>>
>>
>>
>> Is there a formula to calculate the required number of primary
>> turns to get about 1mH inductance from this data? Thanks for
>> any help.
>>
>> cheers,
>> Jamie

>
> Call them and ask what's the Al value. It's amazing that many
> magnetics suppliers don't furnish this. They could also furnish a
> number of other handy electrical and thermal values that are a
> nuisance to calculate, like gauss per ampere-turn and temperature rise
> per watt.

I guess also they might have Al values for different core gaps, or can
this be guesstimated too? I don't know much about using core gaps
for flybacks, is it even necessary to do if you have a core big enough
that it won't saturate without a gap?

cheers,
Jamie

>
> John
>
>
>

legg
Guest
Posts: n/a

 10-26-2007, 11:02 PM
On Wed, 24 Oct 2007 22:43:07 GMT, Jamie Morken <(E-Mail Removed)>
wrote:

>Hi,
>
>I have a flyback transformer design in ltspice with a 1mH primary coil,
>I would like to see how many turns this would require on this transformer:
>
>core size: E375
>
>falco part#: 1831-331-002
>
>cross section area Ac(cm^2) =0.840
>
>magnetic path length (cm) = 6.94
>
>WaAc(cm^4) = 0.856
>
>core volume(cm^3) = 5.830
>
>
>
>Is there a formula to calculate the required number of primary
>turns to get about 1mH inductance from this data? Thanks for
>any help.

You would not normally need AL values for a ferrite core used in a
flyback, as this is determined by the gap required to store the energy
needed.

L = uo x N^2 x Ae / Lg

L = inductance in henries

uo = permeability of free space = 4 x pi x 10E-7

N = turns count

Ae = cross-sectional area at the gap in meters^2

Lg - length of the gap im meters.

.....................................

You have to determine N based on peak core flux change, limited by
core loss or core saturation at the frequency and duty cycle you are
preparing or able to use. To do this you need more core material
information concerning it's power loss characteristics, whether the
material is ferrite or powdered material.

As powdered material has a distributed gap, it will not normally be
merchandised without reference to it's permeability or the part's AL
value

For ferrite parts, if the frequency is lowish or the part is very
small, the flux density will likely be determined by the saturation
limit.

In this case,

Nmin > V x t / ( Bsat x Ae )

Nmin = minimum turns

V = applied voltage in volts

t = period of applied voltage in seconds

Bsat = saturation flux density in Teslas

Ae = minimum cross-sectional area of the ferrite material in meters^2

( Bsat of ferrite ~ 0.33T @ room temperature )
.................................................. .......

You seem already to have determined that 1mH of primary inductance is
desirable, by some method or other. Note that depending on the
operating frequency, a certain peak current will be expected in this
primary inductance in order to deliver the required output power.

This is determined by the rough formula

P = L x Ip^2 x f / 2

P = delivered power and all losses in Watts

L = primary inductance in Henries

Ip = peak primary current in Amps

f = pulse repetition rate in Hertz

cover flyback converters and flyback transformers pretty clearly.

RL

Genome
Guest
Posts: n/a

 10-27-2007, 09:56 PM
On Oct 27, 12:02 am, legg <(E-Mail Removed)> wrote:
> On Wed, 24 Oct 2007 22:43:07 GMT, Jamie Morken <(E-Mail Removed)>
> wrote:
>
>
> You would not normally need AL values for a ferrite core used in a
> flyback, as this is determined by the gap required to store the energy
> needed.
>
> L = uo x N^2 x Ae / Lg
>
> L = inductance in henries
>
> uo = permeability of free space = 4 x pi x 10E-7
>
> N = turns count
>
> Ae = cross-sectional area at the gap in meters^2
>
> Lg - length of the gap im meters.
>

Blork.

So... In the limit as Lg tends to zero inductorance tends to infinity?

What is life like when you get dialed in as low quality?

DNA

legg
Guest
Posts: n/a

 10-28-2007, 12:00 AM
On Sat, 27 Oct 2007 14:56:47 -0700, Genome <(E-Mail Removed)>
wrote:

>On Oct 27, 12:02 am, legg <(E-Mail Removed)> wrote:
>> On Wed, 24 Oct 2007 22:43:07 GMT, Jamie Morken <(E-Mail Removed)>
>> wrote:
>>
>>
>> You would not normally need AL values for a ferrite core used in a
>> flyback, as this is determined by the gap required to store the energy
>> needed.
>>
>> L = uo x N^2 x Ae / Lg
>>
>> L = inductance in henries
>>
>> uo = permeability of free space = 4 x pi x 10E-7
>>
>> N = turns count
>>
>> Ae = cross-sectional area at the gap in meters^2
>>
>> Lg - length of the gap im meters.
>>

>
>Blork.
>
>So... In the limit as Lg tends to zero inductorance tends to infinity?
>
>What is life like when you get dialed in as low quality?
>
>DNA

When the ratio between the lengths of the gap path and the ferrite
path lenths approaches 10E-7, then the permeability of the ferrite
comes into effect.

A gapless ferrite core isn't much use in storing energy, which is what
is intended in a flyback circuit. Whether a 20mW circuit can be said
to have a topology is another thing. erp.

I thought I might get a respnse from Master Jamie, but I guess he's
just fooling around again.

Why didn't you offer a link to your own blither. I recall it being
modestly illuminatin'.

RL

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Optik Electronics Repair 14 11-11-2011 01:38 AM Brad Electronic Repair 0 06-05-2007 07:05 PM Watson A.Name - \Watt Sun, the Dark Remover\ Electronic Components 90 06-14-2004 12:45 PM Watson A.Name - \Watt Sun, the Dark Remover\ Electronic Design 90 06-14-2004 12:45 PM Al Borowski Electronic Design 22 04-12-2004 05:58 AM