Charging method and circuit using indirect current sensing
View Patent ↗The present invention relates to a charging circuit and method for generating a charging current supplied to an output terminal ( 15 ) to which a battery ( 40 ) to be charged is connected. The charging current is indirectly sensed to generate a sensing current having a predetermined relation to the charging current. This sensing current is then compared to a generated predetermined reference current, wherein the charging current is controlled in response to the result of the comparison. Thereby, accuracy, system costs and power efficiency can be increased as a low-ohmic precision resistor is no longer required in the charge current branch of the circuit. Furthermore, the proposed solution enables a simple implementation of the circuit as an integrated circuit.
1. A charging circuit for generating a charging current supply to an output terminal said charging circuit comprising:
a current mirror comprising first and second transistors connected in a current mirror configuration, the first transistor coupled in series with a charging current supply line that is configured to carry the charging current, the second transistor configured to generate a sensing current having a predetermined relation to the charging current that flows through the first transistor;
current generating means configured to generate a reference current;
current comparing means configured to compare that sensing current with said reference current to generate a control signal; and
control means configured to control said charging current in response to said control signal.
2. A circuit according to claim 1 , wherein said predetermined relation is a predetermined fixed fraction.
3. A circuit according to claim 1 , wherein said charging circuit is an integrated circuit, and said current generating means is configured to generate a predetermined reference current based on a current flowing through a predetermined resistor.
4. A circuit according to claim 3 , wherein said predetermined resistor comprises an external resistor connected to said integrated circuit.
5. A circuit according to claim 3 , wherein said current generating means comprises a current digital-to-analog converter configured to supply said reference current as a nominal reference current.
6. A circuit according to claim 3 , wherein said current generating means comprise second current mirror means configured to copy said current flowing through said predetermined resistor.
7. A circuit according to claim 1 , wherein said comparing means comprises summing means configured to supply said reference current and said sensing current.
8. A circuit according to claim 7 , wherein said summing means are configured to convert a difference between said reference current and said sensing current into a control voltage based on which said control signal is generated.
9. A circuit according to claim 1 , wherein said current mirror means comprise first and second transistor means connected in a current mirror configuration, and third transistor means configured to be driven by an amplifier means connected between respective drain or collector terminals of said first and second transistor means.
10. A charging circuit for generating a charging current supply to an output terminal said charging circuit comprising:
sensing means configured to indirectly sense said charging current and configured to generate a sensing current having a predetermined relation to said charging current, the sensing means comprising a first current mirror means for sensing said charging current using a single voltage signal from a path through which the charging current passes, the first current mirror means comprising a first transistor means coupled in series with a charging current supply line that is configured to carry the charging current;
current generating means configured to generate a predetermined reference current;
current comparing means configured to compare that sensing current with said reference current to generate a control signal; and
control means configured to control said charging current in response to said control signal.
11. A circuit according to claim 10 , wherein said predetermined relation comprises a predetermined fixed fraction.
12. A circuit according to claim 10 , wherein said charging circuit is an integrated circuit, and said current generating means is configured to generate a predetermined reference current based on a current flowing through a predetermined resistor.
13. A circuit according to claim 12 , wherein said predetermined resistor comprises an external resistor connected to said integrated circuit.
14. A circuit according to claim 12 , wherein said current generating means comprises a current digital-to-analog converter configured to supply said reference current as a nominal reference current.
15. A circuit according to claim 12 , wherein said current generating means comprise second current mirror means configured to copy said current flowing through said predetermined resistor.
16. A circuit according to claim 10 , wherein said comparing means comprises summing means configured to supply said reference current and said sensing current.
17. A circuit according to claim 16 , wherein said summing means are configured to convert a difference between said reference current and said sensing current into a control voltage based on which said control signal is generated.
18. A circuit according to claim 10 , wherein said current mirror means comprise first and second transistor means connected in a current mirror configuration, and third transistor means configured to be driven by an amplifier means connected between respective drain or collector terminals of said first and second transistor means.
19. A charging method comprising:
indirectly sensing a charging current and generating a sensing current having a predetermined relation to said charging current, the sensing means comprising a first current mirror means for sensing said charging current using a single voltage signal from a path through which the charging current passes, the first current mirror means comprising a first transistor means coupled in series with a charging current supply line that is configured to carry the charging current;
generating a predetermined reference current;
comparing that sensing current with said reference current to generate a control signal; and
controlling said charging current in response to said control signal.
20. The charging method according to claim 19 , wherein said current mirror means comprise first and second transistor means connected in a current mirror configuration, and third transistor means configured to be driven by an amplifier means connected between respective drain or collector terminals of said first and second transistor means.