Flyback converter - winding order

J

Jacques Fournier

Guest
I've designed a 2-watt flyback converter, 12V to 200V, by using a
round RM5 ferrite core with air gap.
I wonder if it is necessary to first wind the primary and then the
secondary on top, or does it make a difference if I do it vice versa,
with the primary on top ?
For example could the efficiency be higher in one way ?

Any idea ? Thank you.
Jacques
 
<Jacques Fournier> wrote in message
news:tiqrv0lnt1dclt9oom70cifp9pm229kcm1@4ax.com...
I've designed a 2-watt flyback converter, 12V to 200V, by using a
round RM5 ferrite core with air gap.

For example could the efficiency be higher in one way ?
Click to expand...
I do not think it matters - often one interleaves the windings for better
coupling thus reducing leakage inductance/losses. In your case, it probably
does not matter - you can try it, though.
 
In article <tiqrv0lnt1dclt9oom70cifp9pm229kcm1@4ax.com>,
Jacques Fournier <> wrote:
I've designed a 2-watt flyback converter, 12V to 200V, by using a
round RM5 ferrite core with air gap.
I wonder if it is necessary to first wind the primary and then the
secondary on top, or does it make a difference if I do it vice versa,
with the primary on top ?
For example could the efficiency be higher in one way ?
Click to expand...
For single output designs, I usually wind the primary first. The Start
(Nearest the core) layer is the switch end. The second (third) layer is
the input voltage. This gives the lowest primary capacitance, since the
former is fairly thick.

If you can, it is usually best to mix the windings together to reduce
leakage inductance.
--
--
kensmith@rahul.net forging knowledge
 
On Mon, 31 Jan 2005 08:11:32 -0700, the renowned Jim Thompson
<thegreatone@example.com> wrote:

On Mon, 31 Jan 2005 15:03:44 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <tiqrv0lnt1dclt9oom70cifp9pm229kcm1@4ax.com>,
Jacques Fournier <> wrote:
I've designed a 2-watt flyback converter, 12V to 200V, by using a
round RM5 ferrite core with air gap.
I wonder if it is necessary to first wind the primary and then the
secondary on top, or does it make a difference if I do it vice versa,
with the primary on top ?
For example could the efficiency be higher in one way ?

For single output designs, I usually wind the primary first. The Start
(Nearest the core) layer is the switch end. The second (third) layer is
the input voltage. This gives the lowest primary capacitance, since the
former is fairly thick.

If you can, it is usually best to mix the windings together to reduce
leakage inductance.
--

When I did that sort of thing I always preferred split bobbins, so
that there was definite insulation between primary and secondary...
but I was designing for a commercial application that had to pass VDE.

...Jim Thompson
Click to expand...
IME, flyback converters that use the feedback winding to regulate just
won't work acceptably without the windings on top of each other-
preferably with one winding sandwiched between two halves of the other
or intermixed. ISTR a degradation from 5% regulation to 30 or 40%.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Mon, 31 Jan 2005 12:47:43 +0100, Frithiof Andreas Jensen wrote:

Jacques Fournier> wrote in message
news:tiqrv0lnt1dclt9oom70cifp9pm229kcm1@4ax.com...
I've designed a 2-watt flyback converter, 12V to 200V, by using a
round RM5 ferrite core with air gap.

For example could the efficiency be higher in one way ?

I do not think it matters - often one interleaves the windings for better
coupling thus reducing leakage inductance/losses. In your case, it probably
does not matter - you can try it, though.
Click to expand...
Yes. I'd wind half the secondary, the primary, and then the other half of
the secondary.

Good Luck!
Rich
 
In article <hiisv094u098p4a35q2gvbt8pi27mj48sf@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[...]
When I did that sort of thing I always preferred split bobbins, so
that there was definite insulation between primary and secondary...
but I was designing for a commercial application that had to pass VDE.
Click to expand...
If you have to pass VDE, you have to live with the leakage inductance. If
not, Putting the windings as close together as other considerations allow
is the way to go on a flybacker.

Any energy that goes into the leakage inductance must be dealt with. With
a slightly tricky snubber, you can put the energy back onto the input
rail. You still loss energy in the switch sloshing the power around.

--
--
kensmith@rahul.net forging knowledge
 
"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:ctm4mj$pm0$2@blue.rahul.net...
..
If you have to pass VDE, you have to live with the leakage inductance. If
not, Putting the windings as close together as other considerations allow
is the way to go on a flybacker.

Any energy that goes into the leakage inductance must be dealt with. With
a slightly tricky snubber, you can put the energy back onto the input
rail. You still loss energy in the switch sloshing the power around.
kensmith@rahul.net forging knowledge
Click to expand...
Hi Ken,
Would you enlighten us on that tricky snubber?
Sounds very interesting. Resistors don't slosh well.
Regards,
Harry
 
In article <0%BLd.1471$Kj4.1413@trnddc09>,
Harry Dellamano <harryd@tdsystems.org> wrote:
"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:ctm4mj$pm0$2@blue.rahul.net...
[....]
a slightly tricky snubber, you can put the energy back onto the input
rail. You still loss energy in the switch sloshing the power around.
kensmith@rahul.net forging knowledge

Hi Ken,
Would you enlighten us on that tricky snubber?
Sounds very interesting. Resistors don't slosh well.
Regards,
Harry
Click to expand...

Basically this is it:

Vin
---------+------------
! !
! )
--- )
^ D1 ) L(working)
! )
! )
! C1 !
+----!!------+
! !
--- !
^ D2 !
! !
) !
) Switch
)
) L(Snub)
)
!
GND


When the switch turns on, L(snub) and C1 go sprong but not much energy is
transfered anywhere. The end of C1 near the diodes ends up with a small
positive voltage on it.

When the switch turns off, the rise is caught at 2*Vin minus a bit and
L(Working) charges C1 from there.

D1, and D2 have to be fairly fast diodes a simple 1N400X won't do here.

--
--
kensmith@rahul.net forging knowledge
 
"legg" <legg@nospam.magma.ca> wrote in message
news:2qutv05bm1agc9hvftppauo8kcs8eibr58@4ax.com...

Please be reminded that the OP is discussing a 2W flyback converter
with a 12V primary.
Click to expand...
Sure - Still might be worth the bother if the OP is running off batteries or
something.
 
On Tue, 1 Feb 2005 14:38:44 +0000 (UTC), kensmith@green.rahul.net (Ken
Smith) wrote:

In article <2qutv05bm1agc9hvftppauo8kcs8eibr58@4ax.com>,
legg <legg@nospam.magma.ca> wrote:
[....]
Please be reminded that the OP is discussing a 2W flyback converter
with a 12V primary.

Are you trying to imply that overkill is a bad thing?

When we vary from the specific, the likelihood of wasting time is
Click to expand...
increased. His inquiry was pretty specific.

Designing for ruggedness can make sense. Overkill is just overkill.

RL
 
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