A driver for driving laser or a modulator comprises a switch block for switching a current to the laser or modulator and a voltage converter comprising a voltage supply node, an input port for connecting a laser or modulator supply voltage and an output port connected to the switch block. The voltage converter comprises a voltage replica block adapted for generating a pre-defined voltage and is adapted for equalizing DC voltages in the driver by using the pre-defined voltage. The pre-defined voltage approximates the threshold voltage drop of a laser when the driver is connected with a laser or approximates the bias voltage over a modulator when connected with a modulator. The driver comprises a balancer comprising a dummy load connected to the switch block adapted for equalizing voltages in the switch block.