The William Gaatjes electronic library thread.

William Gaatjes · Jun 8, 2012

William Gaatjes · Jun 8, 2012

Handy to keep with you on your android phone, Iphone, tablet or laptop.

dwell · Jun 8, 2012

This is the most awesome thread ever on HT. Thanks!

William Gaatjes · Jun 8, 2012

I knew you would enjoy it. ^_^
As many will enjoy it as well.

William Gaatjes · Jun 16, 2012

I made some pictures from a flyback transformer core to show the idea behind it.

Flyback transformers are a special type of transformers for Switched Mode Power Supplies.
When using a normal smps transformer, a changing current in the primary windings induces a changing magnetic field in the magnetic core. This changing magnetic field is then inducing a changing current in the secondary winding. The material the core is made form is especially chosen that the magnetic field lines can pass through it as was it an almost ideal path for the magnetic field lines. But at the same time, the induced eddy currents in the core are kept as low as possible. Ferrite for example has such properties.

A flyback transformer works differently.
When a changing current is flowing through the primary winding, the induced magnetic field is stored in a small gap inside the core of the transformer.
When the primary current is reducing again, the magnetic energy in this gap is inducing a current in the secondary winding.
This magnetic field is then released again because it induces a current inside the secondary winding. A transfer of energy in steps.
The gap is a storage for magnetic energy. The magnetic field lines have an almost ideal path because of the core, but experience a barrier at the gap. There is a core to air to core transition. Here all the magnetic field lines experience a great "resistance" and the magnetic field is very strong.
The "fringing" field can allow for huge eddy currents to flow. When designing, this must be taken into account because it is not uncommon that the copper windings get hot enough to melt the insulation or even the copper wire itself.
The gap is present in the middle of the 2 E shaped parts of the core.

William Gaatjes · Jun 16, 2012

Added some more pdf files to the first post.

William Gaatjes · Jul 1, 2012

Added some more information.

William Gaatjes · Jul 4, 2012

Added more VHDL information about the inner workings of an fpga.

William Gaatjes · Sep 29, 2012

Added a section about Surface Mount Technology : SMT.

Abwx · Oct 13, 2012

William Gaatjes said:
I made some pictures from a flyback transformer core to show the idea behind it.

Flyback transformers are a special type of transformers for Switched Mode Power Supplies.

A flyback transformer works differently.

There s no such thing as a flyback transformer but there is
flyback switching mode power supplies that use dedicated
transformers , but still , they work the same way as any
other SMPS transformers.

William Gaatjes · Oct 14, 2012

Abwx said:
There s no such thing as a flyback transformer but there is
flyback switching mode power supplies that use dedicated
transformers , but still , they work the same way as any
other SMPS transformers.

That is strange, Wurth Electric provides different models of transformers. With air gap specially for such flyback designs. And without air gap for normal smps applications.
The smps pdf articles in this thread mention the same thing.

And this wiki mentions the same principle.
http://en.wikipedia.org/wiki/Flyback_transformer

Unlike mains transformers and audio transformers, a LOPT is designed not just to transfer energy, but also to store it for a significant fraction of the switching period. This is achieved by winding the coils on a ferrite core with an air gap. The air gap increases the reluctance of the magnetic circuit and therefore its ability to store energy.

The current does not flow simultaneously in primary and secondary (output) windings. Because of this the flyback transformer is really a loosely coupled inductor rather than classical transformer, in which currents do flow simultaneously in all magnetically coupled windings.

What do you mean exactly ?

William Gaatjes · Apr 10, 2013

When designing any circuit with transformers(such as smps circuits or transformer based gate drive circuits), keep this in mind :
"
Question :
What is Volt Second (VS) balance and what is its importance?

Answer:
In switching power supplies it is important that your magnetics such as transformers and inductors do not lose their magnetic properties. To ensure that a magnetic core does not saturate the magnetic is design to dissipate all of it's average stored magnetic flux over each switching cycle of the Pulse Width Modulator. This is what is known as VS balance. The average VS applied to a magnetic during the switch on time must equal the VS across the magnetic during the off time. If this principle is not followed the magnetic core will saturate and your magnetic will act as a short.
"

http://www-k.ext.ti.com/srvs/cgi-bi...8-84e0-8167176a4ed9},kb=analog,case=15106,new

Because you store energy in the transformer core, especially in unipolar driven transformers... Measures must be taken to prevent the magnetic core from saturating.
When you store or transfer energy, you must use it or allow the transformer to "reset". This means that there must be no remanent magnetism present.
Or slowly, the core will saturate over time with each applied pulse.
Therefore, the pulse-width applied (duty cycle), is limited.

William Gaatjes · Dec 23, 2013

Reading my own post and the one from Abwx, i felt i needed to add one more post. The trick with a flyback smps is that the secondary winding is electrically reverse connected. See the dots inside the example schematic. This way when current flows into the primary winding, no current can flow through the secondary winding because of the diode blocking the current, the current has the wrong polarity . When the current flow through the primary winding is stopped, the current starts flowing through the secondary winding because of the magnetic flux inside the core. The self induction.

I made a small test circuit with a normal transformer and a flyback transformer. Compared the results and it works just better with a flyback transformer. The output voltages are higher.

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