Stability analysis of a LEDs dimming circuit: An interaction between an LC input filter and a buck converter

This paper proposes an average modeling of LED dimming circuit controlled by a indirect sliding mode technique. Circuit and control parameters that affect an LED dimming system´s stability are studied. The dimming circuit comprises an output-capacitor less buck converter and strings of LEDs as load. The advantages of this topology are: low-part count and increment of system lifetime. This dimming circuit is connected to a 48 V power source via an LC filter to reduce the input ripple current. It is known that tightly regulated dc-dc converter might lead to unstable operation of the system due to its negative input resistance characteristic. This paper proposes the guidelines to choose the control parameters of the sliding control that includes dynamics of a DC bus due to the change of the operating point of LED. The theoretical model is validated through experimental results obtained from the test bench using two strings of 5 Z-power W42182 LEDs (V_F = 3.25V, I_F = 1A).