I am determining the Area-Product of the core required for a transformer to be used within a series resonant converter. The specifications are as follows:

• Switching frequency = 400 kHz
• Primary current = sine wave with a peak value of 500 mA
• Power output = 1 W

These are my calculations:

• I decided to use a core made out of N49 (since many such cores are already available)
• From the data given on this website, I have determined the saturation flux density of the ferrite core as: 0.04 T (approx.)
• The winding factor is considered to be 0.2
• Since we are dealing with 400 kHz, I decided to use a Litz wire with a 44 AWG strand size which has a bare Copper diameter of approximately 0.051 mm
• Since the RMS value of the primary current is 0.353 A, I decided to use a Litz wire with 18 such strands. This may be too much, but it is fine for my initial design (the overall conductor area now comes out to be 0.0368 $mm^2$ ).
• I calculated the current density of this conductor as follows: $J=\frac{0.353\ A}{0.0368\ mm^2}=9.59 \ A/mm^2$
• The Area-Product of the transformer is given by: $AcAw=\frac{VI}{2 f_{sw}\ B_m k_w\ J}$

This gives a value of $\frac{1\ W}{2×(400000\ Hz)×(0.04\times 10^{−6}\ Wb/mm^2)× (0.2) ×(9.59\ A/mm^2)} = 16.293\ mm^4$

I think this calculation is wrong. The website that I mentioned before mentions the max flux density in ferrites at 400 kHz as being close to 0.04 T. Is this correct? Is the chosen current density correct? Also, will there be any issue due to more number of strands (more than the required value) within the wire? Should I use litz wire or just stick to using a solid core AWG 28 wire instead?

NOTE: This transformer will be used in a series resonant converter that will supply power to a sensor module operating at 10 V (This specific topology is used to ensure isolation).

EDIT:

• The core can be considered to be ER 9.5/5 from TDK
• The turns ratio can be taken as 15:10

posted about 1 year ago

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1y ago

jonathan_the_seagull‭

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