Circuits for driving light sources

• US 9,439,255 B2
• Filed: 09/11/2015
• Issued: 09/06/2016
• Est. Priority Date: 11/14/2014
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro Incorporated
• Inventors: Liu, Xueshan, Lin, Yung Lin, Kuo, Ching-Chuan
• Primary Examiner(s): Le, Tung X
• Application Number:
  US14/852,047
• Publication Number:
  US 20160143096A1
• Time in Patent Office: 361 Days
• Field of Search: 315/185.R, 315/186, 315/192, 315/193, 315/200.R, 315/294
• US Class Current: 1/1
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A light source driving circuit for powering a first light source and a second light source by a DC voltage includes a first control circuitry and a second control circuitry. If the DC voltage is within a first range, then the first control circuitry controls a first switch and the second control circuitry controls a second switch to turn on the first light source and to regulate a current flowing through the first light source. If the DC voltage is within a second range, then the first control circuitry controls a third switch and the second control circuitry controls a fourth switch to turn on the first light source and the second light source and to regulate a current flowing through the first light source and the second light source.

Claims

1. A light source driving circuit for powering a first light source and a second light source by a DC (direct current) voltage, comprising:

a first control circuitry coupled to said first light source and said second light source; and

a second control circuitry coupled to said first light source and said second light source,

wherein if said DC voltage is within a first range, then said first control circuitry controls a first switch and said second control circuitry controls a second switch to turn on said first light source and to regulate a current flowing through said first light source, wherein said first switch and said second switch are coupled to said first light source,

wherein if said DC voltage is within a second range, then said first control circuitry controls a third switch and said second control circuitry controls a fourth switch to turn on said first light source and said second light source and to regulate a current flowing through said first light source and said second light source, wherein said third switch and said fourth switch are coupled to said second light source,

wherein said first control circuitry and said second control circuitry are both coupled to a first common node which is connected between a cathode of said first light source and an anode of said second light source, and wherein said first control circuitry and said second control circuitry are both coupled to a second common node which is connected to the cathode of said second light source,

wherein a first portion of said current flowing through said first light source flows through said first switch and a second portion of said current flowing through said first light source flows through said second switch if said first light source is on and said second light source is off,

wherein a first portion of said current flowing through said first light source and said second light source flows through said third switch and a second portion of said current flowing through said first light source and said second light source flows through said fourth switch if said first light source and said second light source are turned on.

2. The light source driving circuit of claim 1, wherein said first light source comprises a first number of light emitting diodes and said second light source comprises a second number of light emitting diodes, wherein said first number is greater than said second number.

3. The light source driving circuit of claim 1, wherein said first control circuitry comprises:

a first current regulator, coupled to said first light source, operable for controlling said first switch based on a first current reference and a first sensing signal indicating a level of said first portion of said current flowing through said first light source;

a second current regulator, coupled to said second light source, operable for controlling said third switch based on a second current reference and a second sensing signal indicating a level of said first portion of said current flowing through said first light source and said second light source; and

a controller operable for regulating said first portion of said current flowing through said first light source and said first portion of said current flowing through said first light source and said second light source by controlling said first current regulator and said second current regulator.

4. The light source driving circuit of claim 3, wherein said first control circuitry further comprises:

a first current sensor operable for providing said first sensing signal, wherein said first current sensor comprises a first resistor having a first resistance; and

a second current sensor operable for providing said second sensing signal, wherein said second current sensor comprises a second resistor having a second resistance,

wherein said first current reference is equal to said second current reference, said first light source comprises a first number of light emitting diodes having a first forward voltage and said second light source comprises a second number of light emitting diodes having a second forward voltage, and a ratio of said first resistance to said second resistance is equal to a ratio of said first forward voltage to a sum of said first forward voltage and said second forward voltage.

5. The light source driving circuit of claim 4, wherein if said DC voltage is within said first range then said DC voltage is greater than said first forward voltage and less than a sum of said first forward voltage and said second forward voltage and said first current regulator regulates said first portion of said current flowing through said first light source to a first value, and

wherein if said DC voltage is within said second range then said DC voltage is greater than a sum of said first forward voltage and said second forward voltage and said second current regulator regulates said first portion of said current flowing through said first light source and said second light source to a second value, wherein said second value is less than said first value.

6. The light source driving circuit of claim 3, wherein said first control circuitry further comprises:

a first current sensor operable for providing said first sensing signal, wherein said first current sensor comprises a first resistor; and

a second current sensor operable for providing said second sensing signal, wherein said second current sensor comprises a second resistor,

wherein a resistance of said first resistor is equal to a resistance of said second resistor, said first light source comprises a first number of light emitting diodes having a first forward voltage, said second light source comprises a second number of light emitting diodes having a second forward voltage, and a ratio of said first current reference to said second current reference is equal to a ratio of a sum of said first forward voltage and said second forward voltage to said first forward voltage.

7. The light source driving circuit of claim 6, wherein if said DC voltage is within said first range then said DC voltage is greater than said first forward voltage and less than a sum of said first forward voltage and said second forward voltage and said first current regulator regulates said first portion of said current flowing through said first light source to a first value, and

wherein if said DC voltage is within said second range then said DC voltage is greater than a sum of said first forward voltage and said second forward voltage and said second current regulator regulates said first portion of said current flowing through said first light source and said second light source to a second value, wherein said second value is less than said first value.

8. The light source driving circuit of claim 3, wherein said first current regulator comprises a first operational amplifier, a non-inverting input of said first operational amplifier receives said first current reference, an inverting input of said first operational amplifier receives said first sensing signal, and an output of said first operational amplifier controls said first switch based on said first current reference and said first sensing signal,

wherein said second current regulator comprises a second operational amplifier, a non-inverting input of said second operational amplifier receives said second current reference, an inverting input of said second operational amplifier receives said second sensing signal, and an output of said second operational amplifier controls said third switch based on said second current reference and said second sensing signal, and

wherein said controller comprises a third operational amplifier, a non-inverting input of said third operational amplifier is coupled to said third switch, and an inverting input and an output of said third operational amplifier are coupled to said first switch.