Buck converter for supplying a battery, comprising: - a series connection of a diode and a buck switch, the series connection being connected between a DC bus voltage (V DC) and a ground reference, wherein the cathode of the diode is connected to the DC bus voltage (V DC) and the anode of the diode is connected to the buck switch, - an inductor connected at its first terminal to a connection point between the diode and the buck switch, - a series connection of two resistors (11, 12) connected in parallel to the buck switch - a control circuitry for controlling the buck switch, wherein a feedback path is connected from a connection point between the resistors (11, 12) to the control circuitry, - two output terminals (3, 3'), wherein one of the output terminals (3, 3') is connected to the DC bus voltage (V DC), and the other one of the output terminals (3, 3') is connected to the ground reference, characterized by further comprising - an emergency lighting mode switch connected between a second terminal of the inductor and the other one of the output terminals (3, 3'), wherein, when the battery is connected with a positive pole to the one of the output terminals (3, 3') and with a negative pole to the second terminal of the inductor, the emergency lighting mode switch is configured to: - disconnect the battery from the ground reference in a charging mode of the battery, and - connect the battery to the ground reference in an emergency lighting mode such as to supply from the battery an LED converter stage connectable to the output terminals (3, 3'). - a series connection of a diode and a buck switch, the series connection being connected between a DC bus voltage (V DC) and a ground reference, wherein the cathode of the diode is connected to the DC bus voltage (V DC) and the anode of the diode is connected to the buck switch, - an inductor connected at its first terminal to a connection point between the diode and the buck switch, - a series connection of two resistors (11, 12) connected in parallel to the buck switch - a control circuitry for controlling the buck switch, wherein a feedback path is connected from a connection point between the resistors (11, 12) to the control circuitry, - two output terminals (3, 3'), wherein one of the output terminals (3, 3') is connected to the DC bus voltage (V DC), and the other one of the output terminals (3, 3') is connected to the ground reference, characterized by further comprising - an emergency lighting mode switch connected between a second terminal of the inductor and the other one of the output terminals (3, 3'), wherein, when the battery is connected with a positive pole to the one of the output terminals (3, 3') and with a negative pole to the second terminal of the inductor, the emergency lighting mode switch is configured to: - disconnect the battery from the ground reference in a charging mode of the battery, and - connect the battery to the ground reference in an emergency lighting mode such as to supply from the battery an LED converter stage connectable to the output terminals (3, 3'). - disconnect the battery from the ground reference in a charging mode of the battery, and - connect the battery to the ground reference in an emergency lighting mode such as to supply from the battery an LED converter stage connectable to the output terminals (3, 3').