CIRCUIT AND METHOD FOR DETERMINING A CURRENT

• US 20110133787A1
• Filed: 12/07/2009
• Published: 06/09/2011
• Est. Priority Date: 12/07/2009
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Ball, Alan R.
• Granted Patent: US 8,143,923 B2
• Time in Patent Office: Days
• US Class Current: 327/103
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A power supply circuit having a converter circuit and method for determining a current flowing into the converter circuit. A converter circuit includes an amplifier and a current-to-current converter module. The amplifier has a current sensing element coupled between its inverting and noninverting input terminals. The amplifier generates a sensing signal from a charging current flowing through the current sensing element. The sensing signal is input into the current-to-current converter module, which scales the charging current and modulates the scaled charging current. The current-to-current converter module converts the modulated current to a charging voltage that is representative of the charging current. The charging current is converted to a current that is representative of the input current to converter circuit. The input current to the converter circuit is added to an auxiliary load current to yield the current of the power supply circuit.

Claims

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

converting a charging current into a reflection voltage;

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.

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. The method of claim 3, wherein converting the charging current into the reflection voltage further 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.

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 method for determining an input current of a circuit, comprising:

using a charging current to generate a first current sense voltage;

using the first current sense voltage to generate a charging voltage;

using the charging voltage to scale a drive current; and

converting the scaled drive current to a reflection voltage.

9. The method of claim 8, wherein converting the drive current to the reflection voltage includes filtering the reflection voltage.

10. The method of claim 8, further including:

using an auxiliary current to generate a second current sense voltage;

scaling the second current sense voltage to generate a scaled second current sense voltage; and

summing the scaled second current sense voltage and the reflection voltage to generate a summed voltage.

11. The method of claim 10, wherein using the auxiliary current to generate the second current sense voltage includes:

conducting the auxiliary current through a first impedance having first and second terminals; and

generating the second current sense voltage as a difference voltage between first and second terminals of the first impedance.

12. The method of claim 11, wherein using the first current sense voltage to generate the charging voltage includes scaling the first current sense voltage to generate the charging voltage.

13. The method of claim 8, wherein the charging current flows along a first current path that includes a first impedance.

14. The method of claim 13, further including using an auxiliary current to generate a second current sense voltage, wherein the auxiliary current flows along a second current path that includes a second impedance and excludes the first impedance.

15. 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; 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.

16. The power supply circuit of claim 15, 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.

17. The power supply circuit of claim 16, 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.

18. The power supply circuit of claim 17, 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.

19. The power supply circuit of claim 18, 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.

20. The circuit of claim 19, wherein the current source is a voltage controlled current source.