SLUAAL2 june 2023 UCC256402 , UCC256403 , UCC256404
In the LLC center tapped transformer, if the primary to secondaries leakage inductance are different, we can observe that secondary peak currents can be different during each half of the switching period. This can cause one of the diodes overheating. To avoid this, both the secondary winding voltages has to be tightly coupled with the primary so that leakage inductance variation is very small between these windings.
To see the current imbalance on the secondary side, two simulations are considered. Case one: With the equal coupling between primary and secondary windings which is shown in Figure 1-26 (This figure shows all the T-type equivalent models) and Case 2: With the unequal couplings which is shown in Figure 1-18. The EVM parameters are used for both the simulations: k =0.916, L1=510uH, n=16.5, Cr=30nF, fsw=101.5kHz, Load Resistance=0.8 Ohm. We can observe the secondary side currents imbalance in Figure 1-20 compared to the currents shown in Figure 1-19.