Power Electronics Europe Feb/March 2023

www.epc.co.com POWER TRANSISTORS 21 www.power-mag.com Issue 1 2023 Power Electronics Europe This is because for a similar RDS(on) and voltage rating, GaN transistors offer lower COSS, therefore minimizing the magnetizing current needed to achieve ZVS in as short transition time as possible. As a result, the frequency can be increased to the 1 MHz range enabling size reductions in the passive components while maintaining high efficiency. The uP1966E half-bridge gate drivers used for the primary are an ideal match for this application where a minimum of 80V rating and minimum size and external components are key features. Similarly, the LMG1020 offers a tailored solution for this socket, given its minimum footprint and supporting circuitry required, as well as sufficient strength capable of driving the three paralleled EPC2067 FETs without compromising speed. While the components listed above enable very high operating frequencies in a very compact form, some challenges arise from the different propagation delays between primary and secondary gate drivers. To overcome these mismatches, 3 unique PWM generators with independent dual edge control are used to align the desired synchronization between primary and secondary circuits. Such configuration provides the programmable flexibility needed to ensure a balanced square waveform in the primary, with control of the dead time to realize ZVS in the primary and maintain ZVS/ZCS in the rectifier transistors and minimize circulating energy. Transformer Design The transformer design and choice of core material are driven by the converter requirements, input/output voltage ratio of driver controlling a parallel array of three EPC2067s. All power transistors and gate drivers are in CSP format for minimum size and lowest parasitic elements. The choice of eGaN transistors is especially advantageous in the primary given the low RDS(on) * COSS figure of merit compared to equivalent Si MOSFETs. 3.2 m Ω EPC2218 [5] are used in conjunction with two uP1966E [6], a half- bridge gate driver ICs. For the secondary rectifier, a total of six 40 V rated 1.55 m Ω EPC2067 [7] are used as synchronous rectifiers. These six transistors are divided into two branches, where each branch consists of an LMG1020 [8] low side gate LEFT: Fig. 3 (top) Photo of the test system assembled, (centre) measured waveforms, (bottom) measured efficiency at V in = 48 V