An electrical power converter comprising: a transformer having a primary circuit (3,12) and a secondary circuit (5a, 5b, 6, 7) the primary circuit being energisable by an AC signal to induce a secondary AC signal across the secondary circuit for delivering a load current; detecting circuitry (13, 16, 17) configured to detect: a first electrical signal (I prim) representative of a primary current in the primary circuit; and a second electrical signal (Vcapdiv) representative of a time integral of a voltage (V cap) across the primary circuit; scaling circuitry (18,19) configured to: scale the first electrical signal by a first scaling factor dependent on a leakage inductance (Ls) and a magnetising inductance (Lm) of the transformer to provide a scaled first electrical signal; and scale the second electrical signal by a second scaling factor based on the magnetising inductance of the transformer to provide a scaled second electrical signal; and computational circuitry configured to combine the scaled first electrical signal and the scaled second electrical signal so as effectively to subtract the scaled second electrical signal from the scaled first electrical signal to derive a difference signal which is representative of the load current reflected on to the primary side of the transformer and is accordingly representative of the actual load current. a transformer having a primary circuit (3,12) and a secondary circuit (5a, 5b, 6, 7) the primary circuit being energisable by an AC signal to induce a secondary AC signal across the secondary circuit for delivering a load current; detecting circuitry (13, 16, 17) configured to detect: a first electrical signal (I prim) representative of a primary current in the primary circuit; and a second electrical signal (Vcapdiv) representative of a time integral of a voltage (V cap) across the primary circuit; a first electrical signal (I prim) representative of a primary current in the primary circuit; and a second electrical signal (Vcapdiv) representative of a time integral of a voltage (V cap) across the primary circuit; scaling circuitry (18,19) configured to: scale the first electrical signal by a first scaling factor dependent on a leakage inductance (Ls) and a magnetising inductance (Lm) of the transformer to provide a scaled first electrical signal; and scale the second electrical signal by a second scaling factor based on the magnetising inductance of the transformer to provide a scaled second electrical signal; and scale the first electrical signal by a first scaling factor dependent on a leakage inductance (Ls) and a magnetising inductance (Lm) of the transformer to provide a scaled first electrical signal; and scale the second electrical signal by a second scaling factor based on the magnetising inductance of the transformer to provide a scaled second electrical signal; and computational circuitry configured to combine the scaled first electrical signal and the scaled second electrical signal so as effectively to subtract the scaled second electrical signal from the scaled first electrical signal to derive a difference signal which is representative of the load current reflected on to the primary side of the transformer and is accordingly representative of the actual load current.