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  • Author Author: rscasny
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What Is So Special About a Flyback Transformer?

rscasny

What Is so special about a flyback transformer?

The simple answer is how energy is stored in the gap of its core. Basically, it is a coupled inductor with a gapped core. During every cycle, the input voltage is applied to its primary winding. Energy is stored in the core's gap. It is then released to the secondary, which powers to the load.

imageHow Does A Flyback Transformer Work in a Circuit?

As previously stated, flyback transformers have a gapped core, which stores energy without saturating the core. This energy storage capability is its differentiating factor. It is used in a flyback controller.

Using a MOSFET as a switch, the flyback controller will open and close a MOSFET switch with a duty cycle needed to attain the target output voltage. Refer to the figure on the right. Wihen the switch is closed, current flows through the transformer's primary winding, building up a magnetic field to store energy. The winding's polarity causes the diode connected to the secondary winding (output) to be reverse biased. In this state, energy is not released to the secondary winding or the load. When the MOSFET switch is opened, the magnetic field built up around the primary collapses, thereby transferring the stored energy to the secondary winding, the diode conducts, and the energy flows to the load.

What Kind of Devices use a Flyback Transformer?

Flyback transformers are commonly used in flyback converters for voltage transformation (often, step up) and circuit isolation. But they are used in other devices such as LED lighting, battery chargers, and more.

Would you like to learn more about flyback transformers? 

element14 is enrolling in a program where you would get a free kit of flyback transformers to experiment with. We are giving away some fantastic prizes for the best blogs that describe your experiment and what you learned. Go here to learn more and enroll.

  • in reply to Gough Lui

    LoL Dr Gough, hope you wont be a judge as it looks you gonna give me zero for my blog. 

    Dr Gough, ploy to get selected lol. I have ploy to get prize!

  • in reply to Gough Lui

    I didn't see that, I only saw the downvote from abhishek. I disagreed with just that downvote! Seems perfectly fair to downvote in return if someone deliberately doesn't help or information-hides.

  • in reply to shabaz

    Fine. In that case I retract my downvotes, but I still maintain that there has been nothing presented, of substance, to the argument which is being presented.

    - Gough

  • in reply to abhishek2018

    This just sounds like a ploy to get selected, along with a list of excuses. Anyone can upload a screenshot. Nobody is complaining about using KiCad or paper. Everyone is busy - myself included.

    A quote attributed to Einstein - "If you can't explain it simply, you don't understand it well enough,"

    So far, you haven't even given any indication of what your argument is based on, or why so many authoritative sources are incorrect, as per your assertion. You have yet to provide a single source to back-up your claim and your English expression is very much confused and convoluted. I would be much more inclined to trust conventional wisdom, especially as some arguments are purely in semantics and have no bearing on practical application.

    I would say Power Electronics News gives a good run-down of different topologies in their tutorial and claim the following:
    "A flyback is a Buck-boost from the perspective that it can increase or decrease the output voltage with respect to the input voltage. But a Flyback does a lot more than that. It can also invert the polarity if you want, and most importantly the Flyback can provide galvanic isolation from the input to the output."

    Coil-craft, a manufacturer I respect highly, also claims it to be buck-boost in their Guide to Flyback Transformers.

    The reference from Wurth Elektronik makes it clear, the winding ratio is responsible for this capability and this is a matter of physics.
    "Depending on the winding ratio of the coupled power inductor, the input voltage can be higher, lower or equal to the output voltage."

    Sure, specific transformers can be wound for specific applications and intended for use in certain ways - but that doesn't reflect on the topology's capability or lack thereof. As far as I can tell, flybacks are amongst the most versatile topology, even if efficiency is not their strong point.

    - Gough

  • in reply to abhishek2018

    Negative down-vote should not be used on technical issues. Negative down-vote is for someone deliberately being unhelpful I reckon. This doesn't apply here so it's not nice to down-vote someone simply because they disagree on a technical point.

    Incidentally, if you can, can you simplify the explanation down to a single line or so (as others have done here, i.e. that increasing the turns is still the same topology, nothing else has electrically changed apart from voltage level) because (hopefully) this is not a mega-complicated issue. It sounds like a terminology thing, and should be quickly resolvable.