Method, apparatus, and system for driving LED's

• US 7,579,786 B2
• Filed: 06/04/2007
• Issued: 08/25/2009
• Est. Priority Date: 06/04/2007
• Status: Expired due to Fees

• Current Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Original Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Inventors: Soos, Stephen C.
• Primary Examiner(s): Philogene; Haissa
• Application Number:
  US11/809,944
• Publication Number:
  US 20080297058A1
• Time in Patent Office: 813 Days
• Field of Search: 3151691-1693, 315/291, 315/307, 315/247, 315/224, 315/276, 315/282, 315/312, 315/360, 345/82, 345/88, 345/102, 345/46, 327/108, 327/109
• US Class Current: 315/291
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]
• CPC Class Codes: H05B 45/345 Current stabilisation; Maintaining constant current
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: H05B 45/40 Details of LED load circuits
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A method and apparatus for driving LED'"'"'s is disclosed, comprising the steps of receiving a desired intensity value, wherein the desired intensity value represents the desired intensity for the LED'"'"'s; generating a first switching control signal, wherein the first switching control signal is a pulse width modulated signal whose duty cycle is based on the desired intensity value; switching the LED'"'"'s on and off based on the first switching control signal, wherein the switching takes place when the desired intensity value is less than a first desired intensity value threshold; generating a desired constant current value based on the desired intensity value, wherein the desired constant current value represents the value of the desired constant current to drive the LED'"'"'s; determining an actual constant current value, wherein the actual constant current value represents the value of the actual constant current driving the LED'"'"'s; comparing the actual constant current value with the desired constant current value; and adjusting the output of the primary drive of the LED'"'"'s so that the actual constant current value is equal to the desired constant current value. A system for providing LED backlighting of a display is also disclosed, comprising a first constant current source driver, wherein the constant current source driver comprises a primary drive and a step-up circuit; a first series connection of LED'"'"'s, wherein the LED'"'"'s are driven by the first constant current driver; and wherein the first constant current source provides a forward voltage of 42 volts or greater to drive the first series connection of LED'"'"'s.

Claims

1. A method for driving LED'"'"'s comprising the steps of:

receiving a desired intensity value, wherein said desired intensity value represents the desired intensity for said LED'"'"'s;

generating a first switching control signal, wherein said first switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value;

switching said LED'"'"'s on and off based on said first switching control signal, wherein said switching takes place when said desired intensity value is less than a first desired intensity value threshold;

generating a desired constant current value based on said desired intensity value, wherein said desired constant current value represents the value of the desired constant current to drive said LED'"'"'s;

determining an actual constant current value, wherein said actual constant current value represents the value of the actual constant current driving said LED'"'"'s;

comparing said actual constant current value with said desired constant current value; and

adjusting the output of the primary drive of said LED'"'"'s so that said actual constant current value is equal to said desired constant current value.

2. The method of claim 1, further comprising the steps of:

generating a second switching control signal, wherein said second switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value;

switching said LED'"'"'s on and off based on said second switching control signal, wherein said switching takes place when said desired intensity value is less than a second desired intensity value threshold, and wherein said second desired intensity value threshold is less than said first desired intensity value threshold.

3. The method of claim 1, wherein said step of adjusting said output of said primary drive is made by using pulse width modulation to adjust the duty cycle of said primary drive.

4. The method of claim 1, wherein said LED'"'"'s are connected in a series connection of LED'"'"'s.

5. The method of claim 1, wherein said LED'"'"'s are connected in a parallel bank of series connections of LED'"'"'s.

6. The method of claim 1, wherein said LED'"'"'s are HBLED'"'"'s.

7. An apparatus for driving LED'"'"'s comprising:

means for receiving a desired intensity value, wherein said desired intensity value represents the desired intensity for said LED'"'"'s

means for generating a first switching control signal, wherein said first switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value;

means for switching said LED'"'"'s on and off based on said first switching control signal, wherein said switching takes place when said desired intensity value is less than a first desired intensity value threshold;

means for generating a desired constant current value based on said desired intensity value, wherein said desired constant current value represents the value of the desired constant current to drive said LED'"'"'s;

means for determining an actual constant current value, wherein said actual constant current value represents the value of the actual constant current driving said LED'"'"'s;

means for comparing said actual constant current value with said desired constant current value; and

means for adjusting the output of the primary drive of said LED'"'"'s so that said actual constant current value is equal to said desired constant current value.

8. The apparatus of claim 7, further comprising:

means for generating a second switching control signal, wherein said second switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value; and

means for switching said LED'"'"'s on and off based on said second switching control signal, wherein said switching takes place when said desired intensity value is less than a second desired intensity value threshold, and wherein said second desired intensity value threshold is less than said first desired intensity value threshold.

9. The apparatus of claim 7, wherein said LED'"'"'s are connected in a series connection of LED'"'"'s.

10. The apparatus of claim 7, wherein said LED'"'"'s are connected in a parallel bank of series connections of LED'"'"'s.

11. An apparatus for driving LED'"'"'s comprising:

a timing and control unit;

a first input of said timing and control unit for receiving a desired intensity value, wherein said desired intensity value represents the desired intensity for said LED'"'"'s;

a first output of said timing and control unit for generating a first switching control signal, wherein said first switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value;

a first transistor;

the collector of said first transistor coupled to the output of said LED'"'"'s;

the base of said first transistor coupled to said first output of said timing and control unit for switching said LED'"'"'s on and off based on said first switching control signal, wherein said switching takes place when said desired intensity value is less than a first desired intensity value threshold;

a second output of said timing and control unit for generating a desired constant current value based on said desired intensity value, wherein said desired constant current value represents the value of the desired constant current to drive said LED'"'"'s;

a DC/DC converter;

a first input of said DC/DC converter coupled to the emitter of said first transistor for determining an actual constant current value, wherein said actual constant current value represents the value of the actual constant current driving said LED'"'"'s;

a second input of said DC/DC converter coupled to said second output of said timing and control unit for receiving said desired constant current value;

a primary drive coupled to said DC/DC converter, wherein said DC/DC converter controls the output of said primary drive so that said actual constant current value is equal to said desired constant current value; and

a step-up circuit coupled to said primary drive for supplying constant current to the input of said LED'"'"'s at a stepped-up voltage.

12. The apparatus of claim 11, further comprising:

a third output of said timing and control unit for generating a second switching control signal, wherein said second switching control signal is a pulse width modulated signal whose duty cycle is based on said desired intensity value;

a second transistor;

the collector of said second transistor coupled to a current limiting resistor, said current limiting resistor coupled to said output of said LED'"'"'s;

the emitter of said second transistor coupled to the emitter of said first transistor;

the base of said first transistor coupled to said second output of said timing and control unit for switching said LED'"'"'s on and off based on said second switching control signal, wherein said switching takes place when said desired intensity value is less than a second desired intensity value threshold, and wherein said second desired intensity value threshold is less than said first desired intensity value threshold.

13. The apparatus of claim 11, wherein said LED'"'"'s are connected in a series connection of LED'"'"'s.

14. The apparatus of claim 11, wherein said LED'"'"'s are connected in a parallel bank of series connections of LED'"'"'s.

15. The apparatus of claim 11, wherein said timing and control unit is a microcontroller.

16. The apparatus of claim 11, wherein said primary drive is a push pull driver configuration.

17. The apparatus of claim 11, wherein said step-up circuit is a transformer.

18. The apparatus of claim 11, wherein said step-up circuit is a boost converter topology.