we operate at 100khz as much as possible (The l(res)c(res) resonant freq)....we will vary vin to LLC stage to keep it at or near 100khz.
Short cct load we detect that and just latch off.
when we are on 2-3kw load, we will always be at or near 100khz.
We don't "do" no load...if its no load, then it just turns off and waits for a load to come on to it.
The full bridge LLC design was nicer….less rms current all round, and easier to have a bigger L(res) which the leakage inductance of the transformer did not form a significant part of. So the leakage inductance of the transformer was not so critical. But investors want small, small, small…so they want half bridge LLC.
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So yes, we will first have to wind the LLC transformer and check the leakage inductance of it..If the coupling is say 0.99, typical for an offline transformer, then we will get 12.7uH of leakage inductance, and that will mess us up bad, because it will take the resonant frequency too low, and our transformer wont cope with the extra magnetising current. –And we wouldn’t be able to just reduce the C(res) because then we would be operating too near the “peak of doom”, ie where it suddenly goes into capacitive region when you go less than it in frequency, and our fets diodes would reverse recover and blow us up.
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We saw one competitor had used foil winding as wide as the former, and we thought this was because of conduction loss, but now we think its because you can get less leakage inductance with foil windings
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It’s a shame because we could have this job done and dusted with a full bridge LLC, but they wont let us because of the two extra fets…I wouldn’t mind betting the reduction in heatsink requirement for a full bridge llc would make it smaller in the end anyway