Design of closed-loop buck-boost converter for LED driver circuit

This paper develops a light emitting diode (LED) driver circuit with a buck-boost converter. The forward bias of the LED used was 3.1V~4.3V, and the forward current was 0.7A. Twelve 3W white-light LEDs were driven in series in the proposed circuit. Each LED was operated at 4V and 0.6A using ac 110V that was rectified by a bridge rectifier. It is operated in continuous buck-boost mode and the results are then simulated using IsSpice software. In an LED only 15% to 25% of electrical energy is converted into light; the rest is converted into heat, which increases its temperature. The resistance of an LED varies with temperature, making the circuit unstable. Therefore, a closed-loop voltage control system is used in this paper to increase output voltage stability. The circuit scheme and operation mode will first be explained. Then, the transfer function for calculating the shortest regulation time is derived using the state-space averaging method. MATLAB is applied to execute the whole circuit simulations. Finally, experimental results demonstrate that the power factor of the closed-loop buck-boost converter is 0.998 and the output voltage of the designed controller can be stably maintained at 48V.