Study On Peak I~2C Controlled Buck-based LED Driver

Lighting emitting diode(LED)is widely applied in the industrial facilities including street lighting,vehicle lighting and liquid-crystal display for its high luminous efficiency,long lifespan and good color rendering.As the forward current through LED guarantees its luminescence and lifespan,it is significant to investigate the control strategy for LED drivers to ensure the forward current is highly accurate and constant.Targeting to buck-based LED driver,from the view of the traditional peak-current-mode(PCM)control,the work principle of PCM controlled buck-based LED driver is analyzed to establish its precise discrete-time model.Based on the model,the complex dynamical behaviors of LED driver with the variation of circuit parameters are revealed.The boundary equations are also derived to study the effect of circuit parameters on the stability of LED driver,including its period-doubling bifurcation or operation mode shifting from continuous conduction mode(CCM)to discontinuous conduction mode(DCM).The theoretical analysis is verified through computer simulations and hardware experiments.On the basis of PCM control,a peak I~2C control is proposed and its two implement methods to drive LED with constant current.Comparing the stability and transient response of buck-based LED driver between those two implements,the stability of LED driver with enough bigger equivalent series resistance(ESR)and the application of ramp compensation are analyzed from the time-domain waveforms,which are validated by computer simulations.Finally,the discrete-time model is built up to study the effect of the ESR of output capacitor and weight factor of inductor current in inner control loop on the dynamical behaviors of LED driver.The boundary of its period-doubling bifurcation and operation mode shifting from CCM to DCM is derived,by which the operation region of LED diver is divided.Results show that,the stability margin of LED driver can be narrowed by the decrease of ESR of output capacitor or weight factor of inductor current,which can be extended by introducing ramp compensation,which are verified through computer simulations and hardware experiments.