A drive circuit for an electric motor of the type which forms part of a pump in a hydraulic braking circuit of a vehicle comprises an input node, an output node and a voltage and current regulating circuit which connects the nodes and which varies the voltage and current supplied to the output node from the input node in response to a modulation strategy, the input node in use being connected to a battery supply of a vehicle and the output node connected to one side of the electric motor. The voltage and current regulating circuit comprises a switch mode power supply circuit capable of providing at the output node a voltage that is either above or below the battery supply voltage at the input node.