Discrete-Time Modeling of High Power Asymmetric Half-Bridge LED Constant-Current Driver Controlled by Digital Current Mode

The high-power Asymmetric half-bridge Converter (AHBC) LED constant current driver controlled by digital current mode is a fourth-order system. Static operating point, parasitic resistance, load characteristics, sampling effect, modulation mode and loop delay will have great influence on its dynamic performance. In this paper, the small-signal pulse transfer function of the driver is established by the discrete-time modeling method for two operating points with three modulation modes of trailing-edge, leading-edge and double-edge. And, the effects of parasitic parameters, delay, sampling and load etc. are fully considered in modeling. For a large number of complex exponential matrix operations, the first order Taylor formula is used for approximate calculation after the coefficient matrix is obtained by substituting the data. Then, the designed average current mode compensators based on state-space averaging small-signal model(SSA) are used for analog and digital control, and the loop characteristics and control performance are analyzed. Simulation and experimental comparison results show that the proposed discrete-time model(DTM) can more accurately describe the characteristics of resonant peak, high-frequency dynamic and loop delay, and is very suitable for the design of high frequency digital controller.