Investigation on the small signal characteristic based on the LLC hybrid hysteretic charge control

In this paper, an analytical small-signal model applied for hybrid hysteretic charge (HHC) control has been proposed and analyzed with the advantages over direct frequency control (DFC). Based on the approach of extended describing function method and average concept, for the first time, the systematical analytical open loop transfer functions from control to output, input to output, output impedance and the closed transfer functions of the overall loop, audio susceptibility and output impedance are proposed and verified through simulation. Additionally, some important physical insights have been extracted, analyzed and verified. Finally, the experiments on a design example of 12 VDC&12 A output power are conducted and verified. It shows that the calculations match well with the results from both the simulation and experiment, which reveals the proposed analytical transfer functions are very useful for the practical power design to achieve good prediction result.