Abstract: The invention relates to a driver circuit (1) for generating a current flow through a light source (5), in particular a laser diode (LD), to a method for operating the driver circuit (1) and to an ophthalmological laser treatment device comprising such a driver circuit (1). A voltage source (3), the light source (5), a series resistor and a switch are arranged in an electric circuit (2). To generate a series resistance which can be controlled or regulated in discrete stages for the light source (5), the electric circuit (2) is branched into at least two parallel branch circuits (21, . . . , 2N), and there is at least one connectable series resistor (R1, . . . , RN) in each branch circuit (21, . . . , 2N).