Closed loop current control circuit and method thereof

• US 20040036418A1
• Filed: 08/21/2002
• Published: 02/26/2004
• Est. Priority Date: 08/21/2002
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Rooke, Alan Michael, Kandah, Ibrahim S.
• Granted Patent: US 6,798,152 B2
• Time in Patent Office: Days
• US Class Current: 315/77
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A circuit and method for providing closed loop control using constant current switching techniques is disclosed herein. By controlling the current supplied to high intensity light emitting diodes (LEDs) using the techniques and circuits described, high intensity LEDs can be operated at or near their maximum capacity without danger of overloading the LEDs, and without using excess amounts of current. A circuit as described herein, has multiple high side switches, each of which is connected to an LED array. The LED arrays are in turn connected through an inductor to a current switching control section that switches current to ground, or recirculates the current to maintain LED current flow within a desired range.

Claims

1. A circuit comprising:

a first current limiting switch having an enable node and an output node, the first current limiting switch to limit an amount of current provided at the output node to a first predefined amount;

a first output port coupled to the output node of the first current limiting switch;

a second current limiting switch having an enable node and an output node, the second current limiting switch to limit an amount of current provided at the output node to a second predefined amount;

a second output port coupled to the output node of the second current limiting switch;

a first input port;

a sensor including;

an input coupled to the first input port;

an output to provide an indication of an amount of current received at the input;

a current limiter including;

a current input coupled to said output of said sensor;

a control input to receive a control;

a first current output node to provide current received at the current input when a signal at the control input is asserted; and

a second current output node to provide current received at the input when the signal at the control input is deasserted.

2. The circuit as in claim 1, wherein said current limiter further includes:

a controller coupled to said control input, said controller including;

an input coupled to said sensor, said input to receive the indication provided by said sensor; and

logic having an input coupled to said input of the controller, and an output coupled to the control input of the current limiter, said logic to assert and deassert the signal based on the indication;

a transistor including;

a first current electrode coupled to said first current output node of the current limiter;

a second current electrode coupled to said second current output node of the current limiter; and

a control node coupled to said output of said logic.

3. The circuit as in claim 1, wherein said sensor includes a resistor.

4. The circuit as in claim 1, wherein the signal is asserted when the amount of current indicated is more than about +/−

20% different from a nominal amount of current.

5. The circuit as in claim 1, wherein the signal is asserted when the amount of current indicated is more than about +/−

10% different from a nominal amount of current.

6. The circuit as in claim 1, wherein the signal is asserted when the amount of current indicated is more than about +/−

5% different from a nominal amount of current.

7. The circuit as in claim 1, further including:

a first supply input;

a second supply input;

a switch-controller including;

a first input coupled to said first supply input;

a second input coupled to said second supply input;

logic coupled to said first input and said second input to assert a control signal based on which of said first supply input and said second supply input has a voltage present thereon;

a first output coupled to said logic and to said enable node of said first current limiting switch; and

a second output coupled to said logic and to said enable node of said second current limiting switch.

8. The circuit as in claim 7, further including:

a first diode coupled between said first supply input and said first current output node; and

a second diode coupled between said second supply input and said first current output node.

9. The circuit as in claim 1, further including:

a first light emitting diode (LED) array coupled to said first output port;

a second LED array coupled to said second output port, wherein said first LED array and said second LED array are electrically parallel; and

an inductor coupled in series between said first and second LED arrays and said first input port.

10. The circuit as in claim 1, further including a diode coupled in series with said current limiter, said diode to provide reverse-bias protection.

11. The circuit as in claim 1, wherein said circuit is an automotive tail-light controller.

12. The circuit as in claim 1, wherein a current limit of said current-limiting switches is adjustable.

13. A circuit comprising:

a plurality of first contacts to be coupled to a plurality of light emitting diodes (LEDs);

a plurality of switches to selectively provide current to particular contacts of said plurality of contacts;

a switch controller to selectively activate one or more switches of said plurality of switches, to supply current to particular LEDs;

a second contact to be coupled to an inductor coupled in series with the plurality of LEDs;

a current-switch coupled in series between said second contact and a voltage reference node; and

a current-switch controller to change a state of said current-switch based on whether an amount of current flowing through said second contact is within a desired range.

14. The circuit as in claim 13, wherein said current-switch controller includes:

a current sensor to determine the amount of current flowing through said second contact; and

logic to determine when the amount of current is within the desired range.

15. The circuit as in claim 14, wherein said current sensor includes:

a sense resistor coupled in series with said second contact; and

a differential amplifier coupled across said sense resistor.

16. The circuit as in claim 13, wherein said desired range is within about +/−

20% of a combined maximum current rating of said particular LEDs to which current is being supplied.

17. The circuit as in claim 13, wherein said desired range is within about +/−

10% of a combined maximum current rating of said particular LEDs to which current is being supplied.

18. The circuit as in claim 13, wherein said desired range is within about +/−

5% of a combined maximum current rating of said particular LEDs to which current is being supplied.

19. The circuit as in claim 13, wherein said current-switch controller is programmable.

20. The circuit as in claim 13, further including a plurality of power-supply inputs, and wherein:

said switch controller includes logic to sense which of said plurality of power-supply inputs has a voltage present thereon.

21. The circuit as in claim 20, wherein said switch controller further includes logic to activate particular switches in response to a voltage being present on particular power-supply inputs.

22. The circuit as in claim 13, further including a diode coupled between each of said plurality of contacts and said current switch, said diodes to limit the voltage at said second contact.

23. The circuit as in claim 13, further including:

a plurality of LED arrays coupled to said plurality of contacts; and

an inductor coupled in series between said plurality of LED arrays and said second contact.

24. The circuit as in claim 13, further including a diode coupled in series with said current switch, said diode to provide reverse-bias protection.

25. The circuit as in claim 13, further including a plurality of diodes coupled to said plurality of contacts, said plurality of diodes to recirculate current from said inductor to said plurality of switches.

26. The circuit as in claim 13, wherein said circuit is an automotive tail-light controller.

27. The circuit as in claim 13, wherein said plurality of switches are current-limiting switches.

28. The circuit as in claim 27, wherein a current limit of said current-limiting switches is adjustable.

29. A circuit comprising:

a first port to be coupled to a first side of a voltage supply;

a second port to be coupled to a second side of the voltage supply;

a third port to be coupled to a light emitting diode (LED) array;

a fourth port to be coupled to an inductor;

a first transistor including;

a first current electrode;

a second current electrode coupled to said second port;

a control node;

a resistor having a first end coupled to said fourth port and a second end coupled to said first current electrode of said first transistor;

a second transistor including;

a first current electrode coupled to said third port;

a second current electrode coupled to said first port; and

a control node;

a recirculator coupled in series between said first port and said second end of said resistor;

a first controller including;

a differential amplifier coupled across said resistor to determine a voltage drop across said resistor;

logic to generate a control signal based on said voltage drop;

an output coupled to said logic and to said control node of said first transistor;

an input coupled to said logic;

a second controller including;

an input coupled to said first port;

logic coupled to said input to determine when a voltage is present at said first port;

a first output coupled to said logic and to said control node of said second transistor; and

a second output port coupled to said logic and to said input port of said first controller.

30. The circuit as in claim 29, wherein said logic of said first controller is to generate a control signal when the voltage drop across said resistor indicates that current flowing through said third port is outside of a range of about +/−

20% of a maximum current rating of said LED array.

31. The circuit as in claim 29, wherein said logic of said first controller is to generate a control signal when the voltage drop across said resistor indicates that current flowing through said third port is outside of a range of about +/−

10% of a maximum current rating of said LED array.

32. The circuit as in claim 29, wherein said logic of said first controller is to generate a control signal when the voltage drop across said resistor indicates that current flowing through said third port is outside of a range of about +/−

5% of a maximum current rating of said LED array.

33. The circuit as in claim 29, wherein said logic of said first controller is programmable.

34. The circuit as in claim 29, wherein said recirculator includes a diode.

35. The circuit as in claim 29, wherein said recirculator includes a synchronous switch.

36. The circuit as in claim 29, further including:

a plurality of first ports to be coupled to a first side of a plurality of voltage supplies;

a diode coupled in series between each of said plurality of first ports and said second end of said resistor;

a plurality of third ports to be coupled to a plurality of LED arrays;

a plurality of second transistors to selectively provide current to particular ones of said LED arrays; and

wherein

said second logic is to selectively activate particular second transistors of said plurality of second transistors when a voltage is present at particular first ports.

37. The circuit as in claim 29, further including:

an LED array coupled to said third port; and

an inductor coupled in series between said LED array and said fourth port.

38. The circuit as in claim 29, further including a diode coupled in series with said first transistor and said resistor.

39. The circuit as in claim 29, further including:

a fifth port to be coupled to a blocking capacitor; and

a diode coupled in series between said first port and said fifth port to provide an internal voltage rail.

40. The circuit as in claim 29, wherein said circuit is an automotive tail-light controller.

41. The circuit as in claim 29, further including a current limiter coupled from said first current electrode of said second transistor to said second current electrode of said second transistor.

42. The circuit as in claim 41, wherein a current limit of said second transistor is adjustable.

43. A method comprising:

supplying current to selected LED arrays of a plurality of LED arrays;

combining the current supplied to the selected LED arrays into a combined current;

passing the combined current through an inductor;

determining an amount of current passing through the inductor;

de-activating a current-switch when the amount of current passing through the inductor is determined to be greater than an upper limit;

routing the inductor current to the selected LED arrays when the current-switch is deactivated;

activating the current-switch when the amount of current passing through the inductor is determined to be less than a lower limit; and

passing the inductor current to ground when the current-switch is activated.

44. The method as in claim 43, wherein supplying current to selected LED arrays includes activating selected switches associated with the selected LED arrays.

45. The method as in claim 44, further including limiting an amount of current flowing through the activated switches.

46. The method as in claim 43, wherein supplying current further includes:

sensing a supply voltage on selected supply lines of a plurality of supply lines; and

activating selected switches based on which of the plurality of supply lines has a voltage sensed thereon.

47. The method as in claim 43, wherein determining the amount of current passing through the inductor includes measuring a voltage drop across a sense resistor coupled in series with the inductor.

48. The method as in claim 43, wherein the upper limit is up to about 20% greater than a combined maximum current rating of the selected LED arrays to which current is being supplied.

49. The method as in claim 43, wherein the upper limit is up to about 10% greater than a combined maximum current rating of the selected LED arrays to which current is being supplied.

50. The method as in claim 43, wherein the upper limit is up to about 5% greater than a combined maximum current rating of the selected LED arrays to which current is being supplied.

51. The method as in claim 43, wherein the lower limit is up to about 20% less than a combined maximum current rating of the selected LED arrays to which current is being supplied.

52. The method as in claim 43, wherein the lower limit is up to about 10% less than a combined maximum current rating of the selected LED arrays to which current is being supplied.

53. The method as in claim 43, wherein the lower limit is up to about 5% less than a combined maximum current rating of the selected LED arrays to which current is being supplied.

54. The method as in claim 43, wherein the current-switch controller is programmable.

55. The method as in claim 43, wherein routing the inductor current includes passing the inductor current through a plurality of diodes.