An electrical system comprising: a resistive load; a first current source connected to provide a first current to the resistive load, wherein the first current source is a flyback current source; a current-sense resistor connected to the resistive load; a second current source being a high precision current source connected to provide a second current (Ic) to the current-sense resistor such that the current passing through the current-sense resistor is the sum of the first and second currents; a control processor; and a voltage sensor adapted to sense the voltage across the current-sense resistor and provide a sensor signal to the control processor, wherein the control processor is adapted to control the first and second current sources (202, 216) based on the sensor signal, wherein: the second current source is adapted to provide an initial current level; and the control processor is adapted to raise the first current by a specified current increase by: raising the second current (Ic) by the specified current increase; setting a reference voltage (Vs) substantially equal to the voltage across the current-sense resistor; reducing the second current (Ic) until the second current is substantially equal to the initial current level; and raising the first current until the voltage across the current-sense resistor is substantially equal to the reference voltage (Vs), wherein the initial current level is zero amperes. a resistive load; a first current source connected to provide a first current to the resistive load, wherein the first current source is a flyback current source; a current-sense resistor connected to the resistive load; a second current source being a high precision current source connected to provide a second current (Ic) to the current-sense resistor such that the current passing through the current-sense resistor is the sum of the first and second currents; a control processor; and a voltage sensor adapted to sense the voltage across the current-sense resistor and provide a sensor signal to the control processor, wherein the control processor is adapted to control the first and second current sources (202, 216) based on the sensor signal, wherein: the second current source is adapted to provide an initial current level; and the control processor is adapted to raise the first current by a specified current increase by: raising the second current (Ic) by the specified current increase; setting a reference voltage (Vs) substantially equal to the voltage across the current-sense resistor; reducing the second current (Ic) until the second current is substantially equal to the initial current level; and raising the first current until the voltage across the current-sense resistor is substantially equal to the reference voltage (Vs), wherein the initial current level is zero amperes. raising the second current (Ic) by the specified current increase; setting a reference voltage (Vs) substantially equal to the voltage across the current-sense resistor; reducing the second current (Ic) until the second current is substantially equal to the initial current level; and raising the first current until the voltage across the current-sense resistor is substantially equal to the reference voltage (Vs), wherein the initial current level is zero amperes.