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I'm going to design an SMPS, in which 120V High frequency AC will be step down to 48V AC high frequency (50KHz) using HF Transformer and then rectified.

I have done the calculation for HF transformer design(120V to 48V AC,50KHz). When I gave the design to manufacture, he told me that HF transformer design varies based on type of switch used for inverter in primary side. I would like to know whether that is true.

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    \$\begingroup\$ The other question that comes to me is why you are not right away producing 48V but instead go through a 12V step... \$\endgroup\$
    – PlasmaHH
    Dec 13, 2017 at 8:46
  • \$\begingroup\$ Need isolation.so instead of direct conversion,using transformer \$\endgroup\$ Dec 13, 2017 at 8:52
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    \$\begingroup\$ @SivaNatrajan that is not a reason to not go directly to 48V. \$\endgroup\$ Dec 13, 2017 at 8:53
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    \$\begingroup\$ @Bimpelrekkie: "12V AC high frequency (50KHz)" he says, doesn't sound like a buck to me \$\endgroup\$
    – PlasmaHH
    Dec 13, 2017 at 9:03
  • \$\begingroup\$ @PlasmaHH I was misreading, OP does not mention 12 V DC. That would indeed suggest a 12 V AC output flyback converter. But then indeed, why not make 48 V AC directly as the 12 VAC is already mains isolated. \$\endgroup\$ Dec 13, 2017 at 9:13

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There are quite a few considerations in transformer design, but one of the main ones is the requirement to keep the transformer out of saturation. In traditional transformer applications where an ac signal is applied and an ac signal is the result, the transformer input must have no DC component to prevent the core from saturating; in switched mode power supplies, a push-pull circuit is the one that comes to mind where the primary side is always powered. The primary windings must have exactly the same number of turns, and the duty cycle must be exactly 50% to keep the DC bias from affecting the transformer performance. In most other topologies, the transformer is really an inductor that is charged by the primary and discharged into the secondary so that both the input and output are not continuous. In these cases, the transformer's inductance must be controlled, either by means of a gap in the core or by using a core material that performs the same function as gapping.

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