Circuit and method for determining a current

1. A method for determining a system current in a circuit that includes a converter circuit, comprising:

splitting the system current into an input current and an auxiliary current, wherein the input current flows through a first resistor and a first energy storage element and the auxiliary current flows through a second resistor, and wherein a second energy storage element is absent from a current flow path of the auxiliary current;

converting a charging current into a reflection voltage representative of the input current;

converting the auxiliary current into a summer input voltage; and

adding the reflection voltage to the summer input voltage to generate a charger input voltage that is representative of the system current.

2. The method of claim 1 , wherein converting the auxiliary current into the summer input voltage comprises amplifying a first difference voltage to generate the summer input voltage.

3. The method of claim 2 , wherein converting the charging current into the reflection voltage comprises generating a second difference voltage and further including amplifying the second difference voltage to generate a scaled current sense voltage.

4. A method for determining a system current in a circuit that includes a converter circuit, comprising:

converting a charging current into a reflection voltage, wherein converting the charging current into the reflection voltage includes:

generating a pulse width modulated control voltage;

using the scaled current sense voltage and the pulse width modulated control voltage to generate a reflection current; and

generating the reflection voltage from the reflection current, and

converting an auxiliary current into a summer input voltage; and

adding the reflection voltage to the summer input voltage to generate a charger input voltage that is representative of the system current.

5. The method of claim 4 , wherein converting the charging current into the reflection voltage includes transmitting the charging current through a first impedance element.

6. The method of claim 5 , wherein converting the auxiliary current into the summer input voltage includes transmitting the auxiliary current through a second impedance element.

7. The method of claim 6 , wherein the charging current is absent from the second impedance element when transmitting the charging current through the first impedance element and the auxiliary current is absent from the first impedance element when transmitting the auxiliary current through the second impedance element.

8. A power supply circuit, comprising:

a system path coupled to a first node for receiving a first portion of a current, the system path comprising a first impedance having first and second terminals, wherein an energy storage elements is absent from the system path; and

a battery charging path coupled to the first node for receiving a second portion of the current, the battery charging path comprising a second impedance having first and second terminals and wherein the first impedance is absent from the battery charging path and the energy storage element is present in the battery charging path.

9. The power supply circuit of claim 8 , further including:

a first amplifier having first and second input terminals and an output terminal, the first input terminal coupled to the first terminal of the first impedance and the second input terminal coupled to the second terminal of the first impedance; and

a summer circuit having first and second input terminals, the first input terminal coupled to the output terminal of the first amplifier.

10. The power supply circuit of claim 9 , further including:

a second amplifier having first and second input terminals and an output terminal, the first input terminal coupled to the first terminal of the second impedance and the second input terminal coupled to the second terminal of the second impedance;

a converter circuit having first and second input terminals and an output terminal, the first input terminal coupled to the output terminal of the second amplifier and the output terminal of the converter circuit coupled to second input terminal of the summer circuit; and

a pulse width modulated control circuit having first and second output terminals, the first output terminal coupled to the second input terminal of the converter.

11. The power supply circuit of claim 10 , further including:

a first transistor having first and second current carrying electrodes and a control electrode, the first current carrying electrode coupled to the first node, the second current carrying electrode coupled to the second impedance, and the control electrode coupled to the first output terminal of the pulse width modulated control circuit; and

a second transistor having first and second current carrying electrodes and a control electrode, the first current carrying electrode coupled to the second current carrying electrode of the first transistor and the control electrode coupled to the second output terminal of the control circuit.

12. The power supply circuit of claim 11 , wherein the converter circuit comprises:

a comparator having first and second input terminals and an output terminal, the first input terminal coupled to the first output terminal of the pulse width modulated control circuit;

a third transistor having a control electrode and first and second current carrying electrodes, the control electrode coupled to the output terminal of the comparator;

a current source having a current carrying terminal coupled to the first current carrying electrode of the third transistor; and

a resistor having first and second terminals, the first terminal coupled to the current carrying terminal of the current source.

13. The circuit of claim 12 , wherein the current source is a voltage controlled current source.