Capacitive ladder feed for AC LED

• US 8,841,856 B1
• Filed: 10/03/2013
• Issued: 09/23/2014
• Est. Priority Date: 10/03/2013
• Status: Expired due to Fees

• Current Assignee: Robertson Transformer Company
• Original Assignee: Robertson Transformer Company
• Inventors: Beasley, Denny D.
• Primary Examiner(s): Tan, Vibol
• Application Number:
  US14/045,581
• Time in Patent Office: 355 Days
• Field of Search: 315/185.R, 315/201, 315/192, 315/213, 315/216, 315/217, 315/250, 315/312, 345/102
• US Class Current: 315/253
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix

Abstract

A circuit serving as a light source, the circuit comprising a first group of light-emitting diodes (LEDs), a second group of LEDs connected in anti-parallel with the first group of LEDs, wherein each of the first group of LEDs and the second group of LEDs comprises at least one LED, and a capacitor connected in parallel with the first group of LEDs and the second group of LEDs.

Claims

1. A circuit serving as a light source, the circuit comprising:

a first set of light-emitting diodes (LEDs); and

a second set of LEDs that is connected in series to the first set of LEDs,

wherein the first set of LEDs comprises;

a first group of LEDs;

a second group of LEDs connected in anti-parallel with the first group of LEDs, wherein each of the first group of LEDs and the second group of LEDs comprises at least one LED; and

a first capacitor connected in parallel with the first group of LEDs and the second group of LEDs, and

wherein the second set of LEDs comprises;

a third group of LEDs;

a fourth group of LEDs connected in anti-parallel with the third group of LEDs, wherein each of the third group of LEDs and the fourth group of LEDs comprises at least one LED; and

a second capacitor connected in parallel with the third group of LEDs and the fourth group of LEDs.

2. The circuit of claim 1, wherein each of the first group of LEDs, the second group of LEDs, the third group of LEDs, and the fourth group of LEDs comprises a plurality of LEDs.

3. The circuit of claim 2, wherein no intervening components exist between the first capacitor and the first group of LEDs, wherein no intervening components exist between the first capacitor and the second group of LEDs, wherein no intervening components exist between the second capacitor and the third group of LEDs, and wherein no intervening components exist between the second capacitor and the fourth group of LEDs.

4. The circuit of claim 1, further comprising an inductor connected in series with the first set of LEDs and the second set of LEDs, and wherein the inductor is configured to regulate an overall current flowing through the first set of LEDs and the second set of LEDs.

5. The circuit of claim 4, wherein the inductor comprises a plurality of taps for fractioning an inductance of the inductor.

6. The circuit of claim 4, further comprising an additional capacitor connected in series with the inductor, the first set of LEDs, and the second set of LEDs.

8. The circuit of claim 1, further comprising wiring configured to receive an alternating current (AC) voltage and connected to the first set of LEDs without any intervening AC to direct current (DC) conversion.

9. The circuit of claim 8, wherein the first capacitor and the second capacitor are configured to create a snap action during a transition phase of the AC voltage source such that a voltage across the first set of LEDs and the second set of LEDs has substantially the shape of a square wave.

12. The circuit of claim 1, further comprising multiple additional sets of LEDs, wherein each one of the multiple additional sets of LEDs comprises a capacitor connected in parallel with a group of anti-parallel LEDs, and wherein the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs are connected in series.

13. The circuit of claim 12, wherein each of the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs comprises only two LEDs.

14. The circuit of claim 12, wherein each of the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs comprises more than two LEDs.

15. The circuit of claim 12, further comprising wiring that is connected in series with the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs and that is configured to apply an alternating current (AC) voltage across the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs.

16. The circuit of claim 15, wherein the wiring comprises an inductor and an additional capacitor connected in series with the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs.

17. The circuit of claim 16, wherein the additional capacitor comprises multiple capacitors connected in parallel to each other.

18. The circuit of claim 12, wherein each of the first set of LEDs, the second set of LEDs, and the multiple additional sets of LEDs comprises an LED that is configured to emit light having a color temperature of about 2,500 Kelvin (K) and an LED that is configured to emit light having a color temperature of about 6,000 K.

7. A circuit serving as a light source, the circuit comprising:

a first group of light-emitting diodes (LEDs);

a second group of LEDs connected in anti-parallel with the first group of LEDs, wherein each of the first group of LEDs and the second group of LEDs comprises at least one LED;

a capacitor connected in parallel with the first group of LEDs and the second group of LEDs;

an inductor connected in series with the first group of LEDs and the second group of LEDs, wherein the inductor is configured to regulate an overall current flowing through an anti-parallel set composed of the first group of LEDs, the second group of LEDs, and the capacitor;

an additional capacitor connected in series with the first group of LEDs and the second group of LEDs and in series with the inductor; and

a switch and at least one capacitor connected in series with the switch, wherein the combination of the switch and the at least one capacitor is connected in parallel with the additional capacitor.

10. A circuit serving as a light source, the circuit comprising:

a first group of light-emitting diodes (LEDs);

a second group of LEDs connected in anti-parallel with the first group of LEDs, wherein each of the first group of LEDs and the second group of LEDs comprises at least one LED;

a capacitor connected in parallel with the first group of LEDs and the second group of LEDs; and

wiring configured to receive an alternating current (AC) voltage and connected to the first group of LEDs without an intervening AC to direct current (DC) conversion,

wherein the capacitor is configured to create a snap action during a transition phase of the AC voltage source such that a voltage across the first group of LEDs has substantially the shape of a square wave,

wherein the transition phase occurs when the AC voltage source crosses a zero point, and

wherein the square wave of the voltage across the first group of LEDs causes the first group of LEDs and the second group of LEDs to have a relative off-time of less than 15%.

11. A method for controlling a light-emitting diode (LED)-based light source that operates under an alternating current (AC) source and comprises at least one pair of anti-parallel connected LEDs, the method comprising:

producing an AC voltage across a pair of LEDs to substantially be a square wave shape; and

exciting the pair of LEDs using the AC voltage,

wherein producing the AC voltage comprises using a capacitor connected in parallel with the pair of LEDs to create a snap action near a zero-cross event of the AC source,

wherein the square wave shape of the AC voltage causes the pair of LEDs to have a relative off-time of less than 10%, and

wherein a magnitude of the AC voltage remains smaller than a threshold voltage of the pair of LEDs during the off-time.