The GaN hemt based proof-of-concept is 8mm tall and occupies <5,000mm2.
“GaN is an essential technology for the 800Vdc ecosystem,” claimed EPC CEO Alex Lidow.
While Power Integrations proposes a single half-bridge pair of 1,250V GaN hemts for a similar power supply, EPC is proposing to use eight half-bridges wired in series on the input side (see diagram), sharing the 800V between them as 8x 100V. In this way, only 150V devices are required.
As these are the front ends of eight isolated LLC converters, all their outputs can be wired in parallel to produce a single high-current 12.5V output.
“The LLC modules are designed to operate at the resonant frequency, where efficiency is the highest and the gain of the resonant tank is unity. By designing the resonant inductor [Lr] to be much less than the magnetising inductor [Lm], the gain of the converter remains frequency-independent around the operating frequency and over a wide range,” according to the company. “This forces the parallel outputs to present equal voltages to each of the primaries, including component tolerances , to maintain equally divided voltages across each of the module [inputs]. Since all inputs are in series, the current through each input is identical, balancing the current on each of the outputs.”
One side-effect of this topology is that the transformers only need a 4:1+1 turns ratio, and can be planar.
