Patent ID: 8111014

Claim:
A drive circuit for driving a load, the circuit comprising: an output for connecting the load; a switched mode power supply for supplying at the output a switched output current which increases during ON-intervals and decreases during OFF-intervals; a controller for controlling the switched mode power supply; a current sensor for generating a current sense signal representing the output current; and a voltage sensor for generating a voltage sense signal representing the output voltage of the circuit; wherein the controller comprises: a current sense input receiving the current sense signal, the controller being configured to generate a switching time control signal for the switched mode power supply on the basis of the received current sense signal; a voltage sense input receiving the voltage sense signal; wherein the controller is configured, in response to a change in the received voltage sense signal representing a change in the output voltage, to change the switching time control signal to effectively compensate an effect of the output voltage change on the average value of the output current; at least one threshold voltage generator for generating a threshold voltage; and at least one comparator having a first input receiving a signal equal to or derived from the threshold voltage and a second input receiving a signal equal to or derived from the current sense signal, the controller being configured to generate the switching time control signal so as to indicate a transition moment from an ON-interval to an OFF-interval on the basis of an output signal of the comparator; to change the transition moment in proportion to a change in the received voltage sense signal, so as to delay said transition moment, if the received voltage sense signal increases and to advance said transition moment if the received voltage sense signal decreases; and wherein the controller further comprises a controllable delay between said comparator and said control output, said controllable delay being controlled by a signal equal to or derived from the received voltage sense signal.