hello,

I was trying to build SMPS using switching ic's UC3845 or HVLED007 but ending with less current delivery or poor power factor might be due to improper flyback transformer design. the thing is i don't have the bobbin , core datasheet were i can get all the specs currently i have ETD29,ETD29,EFD30 & ETD34 etc. and some copper wires . is there anyone here who worked on similar project. I just need design calculation or software so i can build my own flyback transformer 24v 2 amp.

 

One rather simple method how to measure the completely uynknown core is to wind some dozen or two dozen of turns and switch to the 50 Hz around 1 Volt adjustable sinwave (Laboratory autotransformer working on 220V to 1 V transformer.

The voltage capacity of the winding is so much fold lesser as the frequency is lesser. For example, 567 Volts 40 kHz means the roughly 1 Volt at 50 Hz. Add the signal form-factor correction 1.1 as the meander is more magnetizing than sin-wave. Then it is so easy to draw the curve - idle current as function of voltage. There find the point where idle current consumes between 5% and 10% of maximum expected full power current, and recalc back how much turns it demand to work the same saturation regime at 40 kHz or what frequency You use. Then, if demand is air gap - may set the gap of guessed thickness and repeat all the measurements adding the DC component of proportional value. Or use from very beginning the formula current multiplied to turn count is Teslas count figure multiplied to bracket magnetic path length via core divided to mju mju zero plus air gap length divided to mju zero, bracket closes.

 

Provided that your core is ferrite, its exact specification won't make much difference as the magnetic circuit is dominated by the reluctance of the gap.
Is 24V @ 2A the input spec or the output spec? If it is the input, what is the output? (and vice versa) Which of those cores are you actually using?

 

Understand that in an application of a "flyback" type transformer, ALL of the energy to be delivered is stored in the core as magnetization energy. So the core is very important.

 

Understand that in an application of a "flyback" type transformer, ALL of the energy to be delivered is stored in the core as magnetization energy. So the core is very important.

The energy is stored in the gap, not in the core, so that is why small variations between marginally different types of ferrite make no difference. As long as it is a “power” ferrite, not a ”signal” ferrite, it will most likely work. However, the size of the gap is really important, but that is a parameter over which you have complete control, by the number of pieces of paper you wedge between the two cores when clamping it together.

 

My experience has been that it is difficult to magnetize air. An air gap is handy for adjusting inductance, but it is difficult to store energy in magnetized air.

 

Provided that your core is ferrite, its exact specification won't make much difference as the magnetic circuit is dominated by the reluctance of the gap.
Is 24V @ 2A the input spec or the output spec? If it is the input, what is the output? (and vice versa) Which of those cores are you actually using?

universal ac input and 24v 2 amp output. i have all the transformers mentioned above.

 

One rather simple method how to measure the completely uynknown core is to wind some dozen or two dozen of turns and switch to the 50 Hz around 1 Volt adjustable sinwave (Laboratory autotransformer working on 220V to 1 V transformer. The voltage capacity of the winding is so much fold lesser as the frequency is lesser. For example, 567 Volts 40 kHz means the roughly 1 Volt at 50 Hz. Add the signal form-factor correction 1.1 as the meander is more magnetizing than sin-wave. Then it is so easy to draw the curve - idle current as function of voltage. There find the point where idle current consumes between 5% and 10% of maximum expected full power current, and recalc back how much turns it demand to work the same saturation regime at 40 kHz or what frequency You use. Then, if demand is air gap - may set the gap of guessed thickness and repeat all the measurements adding the DC component of proportional value. Or use from very beginning the formula current multiplied to turn count is Teslas count figure multiplied to bracket magnetic path length via core divided to mju mju zero plus air gap length divided to mju zero, bracket closes.

For that i need to get one function generator.

 

My experience has been that it is difficult to magnetize air. An air gap is handy for adjusting inductance, but it is difficult to store energy in magnetized air.

So where does an air-cored inductor store energy?

 

There is still a magnetic field in the air, but less energy stored. THAT is why there are not very many air-cored 60Hz power transformers around.

 

There is still a magnetic field in the air, but less energy stored. THAT is why there are not very many air-cored 60Hz power transformers around.

Transformers don’t store energy, inductors do.
Energy stored in a magnetic field = B^2/(2μ)
Permeability of the core is about 3000 x the permeability of the gap, the core is perhaps 100 x the volume of the gap, so the majority of the energy is in the gap.

 

In a flyback transformer especially, the magnetic field is created by a current in the primary. When the current stops, the magnetic field generates the voltage in the secondary. Hence the field is stored in the core material. Why else would there be a core in a power transformer???

 

In a flyback transformer especially, the magnetic field is created by a current in the primary. When the current stops, the magnetic field generates the voltage in the secondary. Hence the field is stored in the core material. Why else would there be a core in a power transformer???

In order to conduct the flux to the ends of the gap, where the energy is stored. The ferromagnetic core has very low reluctance in comparison to the air in the gap, so, applying Hopkinson’s law, most of the magnetomotive force is across the gap.
The flux density in the gap is effectively unlimited. The limiting factor is the saturation flux density of the ferromagnetic core material (about 0.2T for ferrite).
An appropriate reluctance for the device to operate requires a gap in the order of 1mm. Obviously, making the core entirely out of air would result in too high a reluctance, so a ferromagnetic core is requires to conduct the flux around the remainder of the magnetic circuit.

 

In a flyback transformer especially, the magnetic field is created by a current in the primary. When the current stops, the magnetic field generates the voltage in the secondary. Hence the field is stored in the core material. Why else would there be a core in a power transformer???

With all due respect, sir, you misunderstand a fundamental fact about magnetic fields. The field exists primarily in free space, not any permeable materials. Please review your physics textbooks. Unimpeachable fact: one can construct both inductors & transformers without any permeable core material whatsoever! When the flyback's primary current stops, the magnetic field in the GAP collapses, inducing a voltage in the secondary winding of the correct polarity to enable the output rectifier diode to pass current, which extracts the energy from the field. Remember also that the flyback "transformer" is historically mis-named; it is a multi-winding INDUCTOR. Inductors store electrical energy; transformers by design attempt no energy storage, only instantaneous voltage/current transformation.
The purpose of the core is to control the geometry of the magnetic circuit, directing the field to where it needs to be, and preventing [as much as possible] stray fields from leaking into the rest of the universe. This is why high-permeability materials like ferrites & permalloys matter so much - per unit mass one gets much more bang for the buck. But these fancier materials are also much more expensive, which is why we universally use 3%~4% silicon sheet steels in thin laminations as the cores of our 50 or 60 Hz electrical power distribution transformers. No-one really cares too much about the mass or dimensions of a big three-phase utility transformer that will spend its working life bolted down to a concrete pad, but the money cost is uber-important.

 

Ferrite is not as good of a low frequency transformer material as the steel lamination cores are. At higher frequencies they do work better..

 

Ferrite is not as good of a low frequency transformer material as the steel lamination cores are. At higher frequencies they do work better..

That's mainly because the Bsat value of silicon-iron is about 1.8T compared to 0.25T for ferrite, and because of eddy currents in the silicon-iron at high frequency would necessitate the use of very thin laminations. Amorphous silicon-iron with a thickness of 50μm will manage a good 20kHz, but the square-root-of-the-fifth-power relationship between Bpeak and core loss necessitates a low flux density even though Bsat limitations don't. So, if you are limited to 0.25T by core loss, then you might as well use ferrite.

 

I was considering mains power frequencies for laminated iron. 50, 60, and even 400 Hz. Audio transformers are another segment. And then ferrite for multi KILOHERTZ power transformers, used in inverters and switchers.

 

For that i need to get one function generator.

The right function inhabits in the electric network wire. Pure sinus!

 

universal ac input and 24v 2 amp output. i have all the transformers mentioned above.

To organize the under one Volt adjustable source may use the typical laboratory autotransformer (LATR) with switched to it other transformer. If the second`s 220 V bobbin is fed by 11 Volts from LATR, then secondary, say 12 V gets out 12/20=about half Volt what is enough to begin the saturation experiment.

 

That's mainly because the Bsat value of silicon-iron is about 1.8T

All my life I worked with russian cores steels having extreme rarely over 1.2 T, but most having only 1 Tesla. Yet I know that somewhere 1.8 T was invented, I never got an occasion to keep it at hands, except the laser power feeds made in US. Probably Your steel is better than European I guess.