Building Your Own Flyback Transformer

A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Michael

 

[default]

On Wed, 27 Aug 2008 10:15:19 -0700 (PDT), mrdarrett@gmail.com wrote:

A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Michael

Have you put a scope on the primary to see if it is indeed toggling?

I assume your output is from the rectifier diode and filter cap on the
secondary and that one side of the secondary is common to the meter?

Sounds like it ought to have some output if you connected it properly
and it is toggling. The toroid material may not be ideal for the
frequency you are using, but there still should be some output.

Duty cycle problem?

--


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[Rich Grise]

On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:

A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Good Luck!
Rich

 

On Aug 27, 12:00 pm, default <defa...@defaulter.net> wrote:

On Wed, 27 Aug 2008 10:15:19 -0700 (PDT), mrdarr...@gmail.com wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Michael

Have you put a scope on the primary to see if it is indeed toggling?

I have no scope; I thought of using a sound card mic input + resistor,
but the frequency's too high.

I'll cut the frequency down by a factor of 10 (to 7 kHz) and listen
for a hum

I assume your output is from the rectifier diode and filter cap on the
secondary and that one side of the secondary is common to the meter?

Yep

Sounds like it ought to have some output if you connected it properly
and it is toggling. The toroid material may not be ideal for the
frequency you are using, but there still should be some output.

What's the ideal frequency for this toroid material? Is it really
made of ferrite? I'm guessing it was from a noise suppression choke
inductor...

Michael

 

[Eeyore]

mrdarrett@gmail.com wrote:

A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

Well for starters, for flyback you tend to need a core with an air gap !

Go to powerint.com and read all their app notes.

Graham

 

On Aug 27, 12:00 pm, default <defa...@defaulter.net> wrote:


Say... when I wound the secondary, I wound in exactly the same
direction, overlapping the primary.

Was I supposed to wind the secondary in the opposite direction?

Michael

 

[Eeyore]

mrdarrett@gmail.com wrote:

I'm a newbie at flyback transformers. (That's why I'm testing mine at
low voltage, lest I unwittingly emit subatomic particles in my living
room.) Is there a better way to do this, than just have one ultrafast
diode + filter cap in the secondary?

Read some app notes. Google will help.

Graham

 

[Eeyore]

mrdarrett@gmail.com wrote:

What's the ideal frequency for this toroid material?

Depends on the material. Anywhere from 20kHz - 1 GHz.

Is it really made of ferrite?

How would we know ? It might be metal powder. Post a pic of it.

I'm guessing it was from a noise suppression choke
inductor...

Making it completely useless as a power tranformer.

But - for flyback, the biggie is the air gap. That's where the energy is
stored.

Graham

 

[Eeyore]

mrdarrett@gmail.com wrote:

On Aug 27, 12:00 pm, default <defa...@defaulter.net> wrote:

Say... when I wound the secondary, I wound in exactly the same
direction, overlapping the primary.

Was I supposed to wind the secondary in the opposite direction?

Hardly critical if you swap the leads over.

Graham

 

On Aug 27, 1:13 pm, Rich Grise <r...@example.net> wrote:

On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Good Luck!
Rich

The flux hits the diode, can't *quite* break it, then thinks, "Hmm,
maybe I'd better wait here for a few microseconds until the next pulse
arrives."



I'm a newbie at flyback transformers. (That's why I'm testing mine at
low voltage, lest I unwittingly emit subatomic particles in my living
room.) Is there a better way to do this, than just have one ultrafast
diode + filter cap in the secondary?

Michael

 

On Aug 27, 1:13 pm, Rich Grise <r...@example.net> wrote:

On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Good Luck!
Rich

Would use of an ultrafast bridge rectifier avoid the free, all-
expenses paid admission to Saturation-Land?

Michael

 

[John Popelish]

mrdarrett@gmail.com wrote:

What's the ideal frequency for this toroid material? Is it really
made of ferrite? I'm guessing it was from a noise suppression choke
inductor...

There is no industry wide standard for color code of toroids.

Your core could be solid ferrite (high permeability, low
saturation amp turns) or any one of a number of powdered
iron formulas. Based on the heavy wire originally on the
core, I suspect it is powdered iron with lots of air gap
distributed all around the core between the iron grains.

As I said, different manufacturers use different color codes
for their materials. For example:
http://www.elnamagnetics.com/library/catalogs/MHW/MH&W%20International%20Powder%20Cores.pdf
http://www.uoguelph.ca/~antoon/circ/toroids.htm
http://zeus.cedcc.psu.edu/ind/irontoroid.html
http://www.qsl.net/ok1dxd/amidon.htm

A powdered iron core could work for a flyback design if the
permeability were high enough. This doesn't explain your
zero output, though, unless you have a very low permeability
core.

--
Regards,

John Popelish

 

[Joerg]

mrdarrett@gmail.com wrote:

On Aug 27, 1:13 pm, Rich Grise <r...@example.net> wrote:
On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.
I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.
I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.
I got exactly 0 volts out of the secondary.
Why is this?
Is there a minimum voltage requirement for flyback transformers?
Similar effect with 6VDC on the primary side.
At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...
I'm using an NTE587 fast switching diode on the secondary side.
Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Good Luck!
Rich


The flux hits the diode, can't *quite* break it, then thinks, "Hmm,
maybe I'd better wait here for a few microseconds until the next pulse
arrives."



I'm a newbie at flyback transformers. (That's why I'm testing mine at
low voltage, lest I unwittingly emit subatomic particles in my living
room.) Is there a better way to do this, than just have one ultrafast
diode + filter cap in the secondary?

Flyback xfmrs need an airgap, you toroid probably doesn't have one.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[default]

On Wed, 27 Aug 2008 12:36:53 -0700 (PDT), mrdarrett@gmail.com wrote:

On Aug 27, 12:00 pm, default <defa...@defaulter.net> wrote:


Say... when I wound the secondary, I wound in exactly the same
direction, overlapping the primary.

Was I supposed to wind the secondary in the opposite direction?

Michael

It matters not a whit. Only time you care is when the phasing is
critical to the operation - like the winding is a feedback to your
oscillator circuit to keep it running.

Then you just swap the "start" with the "finish" to change the phase -
no need to switch winding direction.

Without a scope you're handicapped. Oops, visually challenged. How
do you know you are driving the toroid with a signal? You can do
things like monitor current or use capacitive coupling and a diode to
rectify the AC so your meter can read it, but a scope is lots better.

You also mentioned you only have 3 volts on the oscillator - you have
to drive the switching transistor on the toroid with enough voltage
and current to get it to saturate - you only need .7 volts with a
bipolar transistor, but with enough current to switch. 70 KHZ might
be too high for the circuit. Tip31 only has a gain of 25 at one amp
collector current.

One easy circuit that almost always works is a blocking oscillator.
One transistor with a tapped primary winding. Phase matters - the
feedback winding has to be out of phase with the collector.

See http://www.cappels.org/dproj/ledpage/leddrv.htm

It isn't a high power circuit - but it can be - lower the bias
resistance and use a cap around the resistor (drives it into
conduction faster and harder). Start with the circuit shown until you
get it working then experiment. The frequency will be dependent on a
lot of factors. In the 50's we used them to drive loudspeakers and
varied the frequency by putting the electrolytic feedback caps in
series with the bias resistor and using variable resistors to change
the pitch - I made a bike horn out of it and used it to look at
resonance in mercury vials.

I wind the toroids with a doubled over piece of magnet wire (bifilar
winding) then connect the start to the finish on one coil - this way I
may still miscount the turns but the center tap will always be in the
center. With ~15 turns of wire and no load on the circuit - the
output can be as much as high as 90-100 - and it will fry a 2N4401
most of the time - so keep the led in the circuit; your TIP31 is only
good for 40 volts.

no need to remove the wire you already have on, just wind over it
--


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[Joerg]

Eeyore wrote:

mrdarrett@gmail.com wrote:

What's the ideal frequency for this toroid material?

Depends on the material. Anywhere from 20kHz - 1 GHz.


Is it really made of ferrite?

How would we know ? It might be metal powder. Post a pic of it.


I'm guessing it was from a noise suppression choke
inductor...

Making it completely useless as a power tranformer.

Not at all, they can work quite well _if_ you keep any DC components out
of the flux.

But - for flyback, the biggie is the air gap. That's where the energy is
stored.

Yep. Best would be to drive this core push-pull and capacitively coupled.

Michael, for heavier loads that can be done using a motor driver chip as
they can be found in printers, disk drives and such. Make sure the
rectification doesn't introduce DC flux and that there is a wee choke
right between rectifier and first capacitor to even out the load on the
driver.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Rich Grise]

On Wed, 27 Aug 2008 13:27:47 -0700, mrdarrett wrote:

On Aug 27, 1:13 pm, Rich Grise <r...@example.net> wrote:
On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.

I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.

I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.

I got exactly 0 volts out of the secondary.

Why is this?

Is there a minimum voltage requirement for flyback transformers?

Similar effect with 6VDC on the primary side.

At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...

I'm using an NTE587 fast switching diode on the secondary side.

Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Would use of an ultrafast bridge rectifier avoid the free, all-
expenses paid admission to Saturation-Land?

I'd have to look it up; I'd probably put "flyback tutorial" or something
in google search.

Good Luck!
Rich

 

On Aug 27, 6:15 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
......

Flyback xfmrs need an airgap, you toroid probably doesn't have one.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Thanks to all for the replies.

Turns out my astable multivibrator wasn't multivibrating at all -
using a 555, I got it to work, kinda. My DMM measured 5VAC across the
secondary. Strange, since this is about what I fed it with on the
input (6VDC, switched, minus the drop from the TIP31A) - but it could
be the high frequency confused my DMM. I was out of alligator clips,
else I would have added the ultrafast diode and cap on the output - I
measured it raw...

More study needed, when I have more spare time... it's the kids'
bedtime now...

Michael

 

[Joerg]

mrdarrett@gmail.com wrote:

On Aug 27, 6:15 pm, Joerg <notthisjoerg...@removethispacbell.net
wrote:
.....

Flyback xfmrs need an airgap, you toroid probably doesn't have one.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.


Thanks to all for the replies.

Turns out my astable multivibrator wasn't multivibrating at all -
using a 555, I got it to work, kinda. My DMM measured 5VAC across the
secondary. Strange, since this is about what I fed it with on the
input (6VDC, switched, minus the drop from the TIP31A) - but it could
be the high frequency confused my DMM. I was out of alligator clips,
else I would have added the ultrafast diode and cap on the output - I
measured it raw...

More study needed, when I have more spare time... it's the kids'
bedtime now...

Just don't expect much out of a TIP31. The 555 doesn't have enough
muscle to drive it properly. So wear goggles, seriously, because with
stuff like this parts can go, in chemistry speak, "exotherm".

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

Paul E. Schoen wrote:

mrdarrett@gmail.com> wrote in message
news:a34eeb18-8547-4c4b-9364-2e79891038ef@q5g2000prf.googlegroups.com...
On Aug 27, 1:13 pm, Rich Grise <r...@example.net> wrote:
On Wed, 27 Aug 2008 10:15:19 -0700, mrdarrett wrote:
A friend gave me a little yellow toroid (ferrite?) with a winding
around it, that he had butchered from some non-working computer part.
I unwound the (thick!) wire, re-wound it with 10 turns of primary, and
50 turns of secondary.
I then built an astable multivibrator switching at 70 kHz, running off
3VDC, switching a TIP31, hoping to get a x5 multiplication of the
voltage.
I got exactly 0 volts out of the secondary.
Why is this?
Is there a minimum voltage requirement for flyback transformers?
Similar effect with 6VDC on the primary side.
At first I thought the yellow ring may be made of plastic, but a
neodymium magnet happily picks up the toroid...
I'm using an NTE587 fast switching diode on the secondary side.
Are you running this single-ended? What provision have you made for
the half-cycle when the transistor is off - where does the flux go?
IOW, how are you resetting the core to prevent it walking away into
saturation-land? ;-)

Good Luck!
Rich

Would use of an ultrafast bridge rectifier avoid the free, all-
expenses paid admission to Saturation-Land?

It does not seem worthwhile to spend time and energy to do experiments on
unknown circuit components, especially without the necessary equipment,
like a scope or an LCR meter. Either of these can be obtained very
inexpensively, especially if you are willing to get an older model and
perhaps do a little repair work (which can be educational as well).

It depends. Sometimes it can be quite sporty to pretend "What if I am on
a lonely island and only my laptop and these few parts?" You can get a
similar circuit going (not with the TIP31 though, and with a forward
concept) using just the sound card and a $2.99 Harborfreight multimeter.

Of course, on that island your laptop battery would croak after two
hours so you've got to be done by then ;-)

But seriously, I was in such situations more than once. Client had a
circuit issue that turned out to be a really nasty noise intrusion from
somewhere. But from where, and what's the path? Next to nothing in
suitable equipment, just my trusty laptop with its 18bit sound card.
However, we needed an iso xfmr that went down to 5Hz and mine quits at
15Hz or so. So we took a mains iso transformer and roached phono jacks
onto it. Of course this just had to be the day the regular OSHA
inspection happened. One engineer turned pale when he saw that. "Put
that away!" ... "Why? We need it right now." ... "Cause the OSHA guy is
next door" ... "Dee-deedle-dum, don't turn around, the commissar's in
town, dee-deedle-dum" ... "Stop that!" (I know the guys quite well, else
I would have pulled that Falco song)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Eeyore]

Joerg wrote:

Eeyore wrote:
mrdarrett@gmail.com wrote:

What's the ideal frequency for this toroid material?

Depends on the material. Anywhere from 20kHz - 1 GHz.

Is it really made of ferrite?

How would we know ? It might be metal powder. Post a pic of it.

I'm guessing it was from a noise suppression choke
inductor...

Making it completely useless as a power tranformer.

Not at all, they can work quite well _if_ you keep any DC components out
of the flux.

Yabbut ! Many of those materials are made intentionally very lossy.

Graham