TIDUF63A December 2023 – June 2024
For this CLLLC converter, a transformer with a turn ratio of 3:8 and leakage inductance of 900nH is used. The HV side has a switching stage in half-bridge configuration with voltage doubler. All switches are based on GaN technology on both LV and HV sides.
To achieve ZVS, the effective parasitic capacitance was derived to calculate the needed magnetizing inductance. The parasitic capacitance of both sides (HV and LV) need to be considered.
The parasitic equivalent capacitance was calculated using the equation from Section 2.3.1:
Based on Equation 5, the maximum LM is 8.5 μH for 100-ns dead time. In this design LM = 6 μH was selected (Bourns 145449).
An additional energy check is required to provide ZVS. Energy stored in the calculated inductance needs to be higher than the energy stored in the COSS.
Observe that the maximum magnetizing inductance is limited by a slew-rate requirement and not by an energy requirement.
This is a fixed frequency converter providing unit gain if operating around the resonance frequency. In this design, the leakage inductor of the transformer is 900 nH. A resonant capacitance of 264 nF was selected. The series resonant frequency can be calculated with Equation 9.
The resulting resonant frequency of the resonant tank is 449 kHz. To avoid parasitics effects the converter operates at slightly below resonant frequency - 400 kHz.
Figure 3-6 shows waveforms of the designed CLLLC converter transferring power from the LV to HV side.