System and method for driving LED

• US 7,583,035 B2
• Filed: 08/13/2007
• Issued: 09/01/2009
• Est. Priority Date: 09/21/2004
• Status: Active Grant

• Current Assignee: Chemtron Research LLC (Intellectual Ventures LLC)
• Original Assignee: Exclara, Inc. (Million Star Technology Ltd.)
• Inventors: Rodriguez, Harry, Shteynberg, Anatoly
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US11/838,186
• Publication Number:
  US 20070285031A1
• Time in Patent Office: 750 Days
• Field of Search: 315/247, 315/246, 315/224, 315/225, 315/209.R, 315/219, 315291-302, 315307-311
• US Class Current: 315/307
• CPC Class Codes: G05F 1/618 using semiconductor devices in series and in parallel with the load as final control devices G05F1/461 takes precedence
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs
• CPC Class Codes: H05B 47/105 in response to determined parameters
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: H05B 47/165 following a pre-assigned programmed sequence; Logic control [LC]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A system drives one or plurality of LEDs regulating their brightness by controlling LEDs average current or voltage. The system includes a switching power converter and an integrated digital regulator with at least one of electrical, thermal and optical feedbacks. The regulator is constructed as a hysteretic peak current mode controller for continuous mode of operation of the power converter. For discontinuous mode of operation of the power converter a pulse averaging sliding mode control is being used. Average LED current is measured by integrating LED pulse current at off time and hysteretically adjusting on time of the power switch. Input battery is protected from discharging at abnormally low impedance of the output.

Claims

1. A system for driving one or plurality of LEDs, comprising:

an energy source;

a power converter for transferring electrical power from said energy source to LEDs in a form of a controlled output current and providing said LEDs brightness regulation, said power converter being constructed as a switching converter, including an inductor, a rectifier, a power switch, operating in a dual phase cycle, having an on phase, when said power switch is closed, exciting said inductor by an input voltage, and an off phase when said power switch is open;

a peak current sensor through said power switch;

a regulator, controlling said dual phase cycle at a variable frequency and a constant off time, coupled to said power converter and receiving feedback signals from at least one of an electrical, thermal or optical sensor for sensing said LEDs performance and comprising;

(i) an LEDs current sensor;

(ii) an integrator with a reset, coupled to said LEDs current sensor for generating an integrated signal over said off phase of said cycle based on said LEDs current signal;

(iii) a divider, coupled to said integrator to divide said integrated signal by a last cycle time;

(iv) a comparator for comparing said integrated and divided LED'"'"'s current signal to a reference signal;

(v) a digital logic, sampling said comparator, resetting said integrator each cycle, measuring said last cycle time and generating a control signal to regulate said LEDs current;

(vi) a D/A converter coupled to said digital logic to convert said control signal from digital to analog form; and

(vii) a current peak comparator, connected to said peak current sensor to compare a peak current to a set point equal to said control signal and turning off said power switch, when said peak current in said power switch reaches a level of a set point;

an oscillator, coupled to said digital logic; and

a buffer to drive said power switch.

2. The system according to claim 1, wherein:

said digital logic increments said control signal once per cycle from one cycle to another by an amount inversely proportional to a difference between said reference signal and an electrical signal from said optical sensor.

3. The system according to claim 1, wherein:

said thermal sensor connected to a reference signal circuit to adjust said reference signal to compensate said LED'"'"'s brightness changes due to temperature effects.

4. The system according to claim 1, wherein:

said energy source is an AC source with a second rectifier.

5. The system according to claim 1, wherein:

said energy source is a DC source or a battery.

6. The system according to claim 1,wherein:

said switching converter is a boost circuit or a buck-boost circuit.

7. The system according to claim 1, further comprising:

an input low voltage protection sub-circuit for turning off said power switch if said input voltage falls below a fixed threshold.

8. The system according to claim 1, further comprising:

a temperature protection sub-circuit for turning off said power switch if a temperature of said regulator exceeds a first fixed threshold and enabling said power switch back to operation when said temperature of said regulator falls below a second fixed threshold, wherein said second fixed threshold is smaller than said first threshold.

9. The system according to claim 1 further comprising:

an isolation power switch, connected between said LEDs and ground to disconnect said LEDs from the said energy source at abnormal modes or system shut down;

an abnormal mode comparator connected between an output and said input voltage and turning off said isolation power switch when said output voltage drops below said input voltage;

a logic to process signals to shut down said isolation power switch either from said abnormal mode comparator or from system shut down; and

a second buffer to drive said isolation power switch.

10. The system according to claim 1 further comprising:

an ambient optical photosensor to adjust said reference signal proportionally to ambient light conditions to regulate a brightness of said LEDs to keep a contrast of an area illuminated by said LED'"'"'s constant.

11. The system according to claim 1, wherein:

said digital logic increments said control signal once per cycle from one cycle to another by an amount inversely proportional to a difference between said reference signal and said integrated LEDs current signal.

12. The system according to claim 1, wherein

said control signal incremented by said digital logic by amounts defined in a look up table, including a fixed minimum level and a fixed maximum level.

13. The system according to claim 1 further comprising:

an overload comparator connected between said LEDs current sensor and an overload set signal to send a signal to said digital logic about fault conditions at said LEDs, wherein said digital logic shuts down said power switch until power reset or turns said power switch on and off to limit an overload current in said LEDs.

14. The system according to claim 13 further comprising:

a zener diode and a resistor connected between an output voltage or an anode of said rectifier and a positive terminal of said overload comparator to provide an output overvoltage protection.

15. An integrated controller to regulate a boost or a buck boost power converter for transferring electrical power from an energy source to LEDs in a form of controlled output current and providing said LEDs brightness regulation, said power converter being constructed as a switching discontinuous current mode converter, including an inductor, a rectifier, an output capacitor, an oscillator, a power switch, operating in a dual phase cycle, having an on phase, when said power switch is closed, exciting said inductor by an input voltage, and an off phase when said power switch is open, fully discharging said inductor, wherein said integrated controller regulating said dual phase cycle at a variable frequency and a constant off time by generating said on phase on time and receiving feedback signals from at least one of an electrical, thermal or optical sensors for sensing said LEDs performance and comprising:

(i) an LEDs current sensor;

(ii) an integrator with a reset, coupled to said LEDs current sensor for generating an integrated signal over said off phase of said cycle of said LED'"'"'s current signal;

(iii) a divider, coupled to said integrator to divide said integrated signal by a last cycle time;

(iv) a comparator for comparing said integrated and divided LEDs current signal to a set reference signal; and

(v) a digital logic, sampling said comparator, resetting said integrator each cycle, measuring said last cycle time and incrementing said on time each cycle from cycle to cycle to turn on and off said primary switch to regulate said LED brightness.

16. The integrated controller according to claim 15 wherein:

said on time generated each cycle by said digital logic for;

a) said LED'"'"'s current smaller than said current signal, as a sum of a last cycle on time and a product of a small time increment by a consecutive number of cycle in progress since said LED'"'"'s current dropped below set reference signal, wherein said on time is limited to a fixed maximum value; and

b) said LED'"'"'s current larger than said set reference signal, as a subtraction of a product of a small time increment by a number minus one of consecutive off time blocks, counted as long as said LEDs current remains larger than said set reference signal, from said last cycle on time, wherein said generated on time is limited to a minimum fixed time value.

17. The integrated controller according to claim 15 further comprising:

a peak current sensor through said power switch; and

a current peak comparator to compare a peak current through said power switch to said set reference signal to limit said peak current through said power switch or to limit a maximum on time, based on value of said input voltage.

18. An integrated controller to regulate a boost or a buck boost power converter for transferring electrical power from an energy source to LEDs in a form of controlled output current and providing said LEDs brightness regulation, a power converter being constructed as a switching discontinuous current mode converter, comprising an inductor, a rectifier, an output capacitor, an oscillator, a power switch, operating in a dual phase cycle, having an on phase, when said power switch is closed, exciting said inductor by an input voltage, and an off phase when said power switch is open, fully discharging said inductor, wherein said controller regulating said dual phase cycle at a variable frequency and a constant off time by generating said on phase on time and receiving feedback signals from at least one of an electrical, thermal or optical sensors for sensing said LEDs performance and comprising:

(i) an LEDs current sensor;

(ii) an R-C filter of said LEDs current;

(iii) a comparator for comparing said filtered LED'"'"'s current signal to a set reference signal; and

(iv) a digital logic, sampling said comparator, incrementing said on time each cycle from cycle to cycle to turn on and off said power switch to regulate said LEDs brightness.

19. The integrated controller according to claim 18 wherein:

said on time generated each cycle by said digital logic for;

a) said LED'"'"'s current smaller than said current signal, as a sum of a last cycle on time and a product of a small time increment by a consecutive number of cycle in progress since said LED'"'"'s current dropped below set reference signal, wherein said on time is limited to a fixed maximum value; and

b) said LED'"'"'s current larger than said set reference signal, as a subtraction of a product of a small time increment by a number minus one of consecutive off time blocks, counted as long as said LEDs current remains larger than said set reference signal, from said last cycle on time, wherein said generated on time is limited to a minimum fixed time value.

20. The integrated controller according to claim 18 further comprising:

a peak current sensor through said power switch; and

a current peak comparator to compare a peak current through said power switch to said set reference signal to limit said peak current through said power switch or to limit a maximum on time, based on value of said input voltage.

21. A system for driving one or plurality of LEDs by transferring electrical power from an energy source to LEDs in a form of a controlled output voltage and providing said one or multiple strings of LEDs voltage regulation, said power converter being constructed as a switching converter, including an inductor, a rectifier, a power switch, operating in a dual phase cycle, having an on phase, when said power switch is closed, exciting said inductor by an input voltage, and an off phase when said power switch is open;

a peak current sensor through said power switch;

a regulator, controlling said dual phase cycle at a variable frequency and a constant off time, coupled to the said power converter and receiving feedback signal from said LEDs, comprising;

(i) a LEDs voltage sensor;

(ii) an integrator with a reset, coupled to said LED'"'"'s voltage sensor for generating an integrated said LED'"'"'s voltage signal over a cycle time;

(iii) a divider, coupled to said integrator to divide an integrated signal by a last cycle time;

(iv) a comparator for comparing said integrated and divided LEDs voltage signal to a reference signal;

(v) a digital logic, sampling said comparator, resetting said integrator each cycle, measuring said last cycle time and generating a control signal to regulate said LED'"'"'s voltage;

(vi) a D/A converter coupled to said digital logic to convert said control signal from digital to analog form;

(vii) a current peak comparator, connected to said peak current sensor to compare a peak current to a set point equal to said control signal and turning off said power switch when said peak current in said power switch reaches a level of said set point; and

an oscillator, coupled to set digital logic.

22. An integrated controller to regulate a boost or buck boost power converter for transferring electrical power from an energy source to LEDs in a form of a controlled output voltage and providing said LEDs brightness regulation, said power converter being constructed as a switching discontinuous current mode converter, including an inductor, a rectifier, an output capacitor, an oscillator, a power switch, operating in a dual phase cycle, having an on phase, when said power switch is closed, exciting said inductor by an input voltage, and an off phase when said power switch is open, fully discharging said inductor, wherein said controller regulating said dual phase cycle at a variable frequency and a constant off time by generating said on phase on time and receiving feedback signal from said LEDs and comprising:

(i) an LEDs voltage sensor;

(ii) an integrator with a reset, coupled to said LEDs voltage sensor for generating an integrated signal over a cycle time, based on said LED'"'"'s voltage signal;

(iii) a divider, coupled to said integrator to divide integrated signal by a last cycle time;

(iv) a comparator for comparing said integrated and divided LED'"'"'s voltage signal to a set reference signal;

(v) a digital logic, sampling said comparator, resetting said integrator each cycle, measuring said last cycle time and incrementing said on time each cycle from cycle to cycle to turn on and off said primary switch to regulate the said LED'"'"'s voltage.