A power switch current estimator comprising: a solid state power switch connected to a control terminal, an input current power terminal, an output current power terminal, and at least one sense wire terminal (20,24), wherein one or more parasitic elements define an electrical pathway between the at least one sense wire terminal (20,24) and the corresponding power terminal (16,18); a driver unit connected to the control terminal and the at least one sense wire terminal, the driver unit selectively turning the power switch on and off; and a current estimator configured to generate an estimated level of current circulating through the solid state power switch in real time in response to one or more switching events, the estimated level of current based on values of at least one of the parasitic elements in order that the estimated level of load current substantially corresponds to an actual level of load current circulating through the solid state power switch; characterised in that: the current estimator comprises a summer configured to determine a weighted average of measured and integrated voltage and current signals with predefined weighting factors based on one or more of the parasitic element values, wherein the measured and integrated voltage and current signals comprise a voltage generated between the output current power terminal and the corresponding sense wire terminal during a power switch turn on or turn off event, a current through the control terminal and a derivative of a voltage between the control terminal and the at least one sense wire terminal. a solid state power switch connected to a control terminal, an input current power terminal, an output current power terminal, and at least one sense wire terminal (20,24), wherein one or more parasitic elements define an electrical pathway between the at least one sense wire terminal (20,24) and the corresponding power terminal (16,18); a driver unit connected to the control terminal and the at least one sense wire terminal, the driver unit selectively turning the power switch on and off; and a current estimator configured to generate an estimated level of current circulating through the solid state power switch in real time in response to one or more switching events, the estimated level of current based on values of at least one of the parasitic elements in order that the estimated level of load current substantially corresponds to an actual level of load current circulating through the solid state power switch; characterised in that: the current estimator comprises a summer configured to determine a weighted average of measured and integrated voltage and current signals with predefined weighting factors based on one or more of the parasitic element values, wherein the measured and integrated voltage and current signals comprise a voltage generated between the output current power terminal and the corresponding sense wire terminal during a power switch turn on or turn off event, a current through the control terminal and a derivative of a voltage between the control terminal and the at least one sense wire terminal. the current estimator comprises a summer configured to determine a weighted average of measured and integrated voltage and current signals with predefined weighting factors based on one or more of the parasitic element values, wherein the measured and integrated voltage and current signals comprise a voltage generated between the output current power terminal and the corresponding sense wire terminal during a power switch turn on or turn off event, a current through the control terminal and a derivative of a voltage between the control terminal and the at least one sense wire terminal.