Light dimmer for LED and incandescent lamps

• US 20050168168A1
• Filed: 02/02/2004
• Published: 08/04/2005
• Est. Priority Date: 02/02/2004
• Status: Active Grant

• Current Assignee: Radiant Power Corp. (Heico Corporation)
• Original Assignee: Radiant Power Corp. (Heico Corporation)
• Inventors: Elliott, Stephen
• Granted Patent: US 7,126,290 B2
• Time in Patent Office: Days
• US Class Current: 315/247
• CPC Class Codes: H05B 35/00 Electric light sources using a combination of different types of light generation
• CPC Class Codes: H05B 39/047 with pulse width modulation from a DC power source
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

The light output intensity of incandescent lamps and LEDs connected to a common lamp power bus are controlled using a composite waveform having two power components: a pulse-width modulated (PWM) component and a direct current DC component. The DC component is maintained below the turn-on voltage for the LEDs. The PWM component controls the light intensity of the LEDs; and the DC component is calculated as a quadrature power series, taking into account that the PWM component contributes to the light intensity of the incandescent lamps. The frequency and slew rate of the PWM component are selected to minimize EMI. A small steady state power component is provided to keep the LEDs slightly turned on to minimize EMI.

Claims

1. Method of dimming both incandescent lamps and LEDs connected to a common lamp power bus, comprising:

with a composite waveform on the power bus, causing light output intensities of the incandescent lamps and of the LEDs to track each other, when being dimmed.

2. Method, according to claim 1, wherein:

the composite waveform comprises two power components;

a pulse-width modulated (PWM) component (V1) having a duty cycle (D) and an alternating current (AC) component (V2).

3. Method, according to claim 1, wherein:

the composite waveform comprises two power components;

a first pulse-width modulated (PWM) component (V1) and a second pulse-width modulated (PWM) component (V2).

4. Method, according to claim 2, wherein:

the second PWM component is of opposite polarity as the first PWM component.

5. Method, according to claim 1, wherein:

the composite waveform contains at least two components, and at least one of the components is sensed by only one of the LEDs and incandescent lamps and is not sensed by the other of the LEDs and incandescent lamps.

6. Method, according to claim 1, wherein:

the composite waveform comprises two power components;

a pulse-width modulated (PWM) component (V1) having a duty cycle (D) and a direct current (DC) component (V2).

7. Method, according to claim 6, wherein:

the DC component is negative with respect to the PWM component.

8. Method, according to claim 6, further comprising:

selecting values for the two power components so that;

the LEDs are unaffected by the DC component;

the PWM component controls the light intensity of the LEDs; and

the DC component is calculated taking into account that the PWM component contributes to the light intensity of the incandescent lamps.

9. Method, according to claim 6, wherein:

the composite waveform is provided by one fast responding power supply.

10. Method, according to claim 6, wherein:

the composite waveform is provided by a variable voltage power suppy for the DC component and a fixed voltage power supply the output of which is PWM modulated, for the PWM component.

11. Method, according to claim 6, wherein:

the PWM component is modulated at a frequency which is compatible with alternating current (AC) power frequencies found in environment of the dimmer.

12. Method, according to claim 6, wherein:

the PWM component is modulated at the mains frequency.

13. Method, according to claim 6, wherein:

a waveform of the PWM component is slew-rate controlled to give edges that rise at rate which is comparable with a slew rate for alternating current (AC) power frequencies found in the dimmer environment.

14. Method, according to claim 6, wherein:

a waveform of the PWM component is modulated using a “

double-edged”

modulation technique.

15. Method, according to claim 6, further comprising:

providing a steady state power component to keep the LEDs slightly turned on.

16. Method, according to claim 6, further comprising:

autodetecting whether one or more LEDs are connected to the power bus, whether one or more incandescent lamps are connected to the power bus, or whether both LEDs and incandescent lamps are connected to the power bus.

17. Method, according to claim 16, wherein:

autodetection is performed by monitoring the power bus during the off time of the PWM component.

18. Method, according to claim 6, wherein multiple (n) output channels are provided for corresponding multiple lamp power busses, further comprising:

phasing the PWM components of the output channels 360/n degrees apart to reduce EMI.

19. Method, according to claim 6, further comprising:

for a given desired output level (L), calculating the PWM component (V1) according to duty cycle (D), and computing the DC component (V2) as a quadrature power solution.

20. Method, according to claim 6, further comprising:

for a given desired output level (L), calculating the PWM component (V1) according to duty cycle (D), and computing the DC component (V2) according to;

$V_2=\sqrt{\frac{{\left(V_{\mathrm{RMS}}\right)}^2-V_{\max }^2<br><br>\left(D\right)}{\left(1-D\right)}}$

wherein;

V_RMS=RMS voltage required in the incandescent lamp to meet the desired illumination level

D=the Duty Cycle)

V_MAX=Supply Voltage

21. Method of controlling light intensity of two different types of lighting devices comprising:

powering the two different types of lighting devices with a composite waveform comprising at least two power components, wherein one of the at least two power components is sensed by only one of the two different types of lighting devices and another of the at least two power components is sensed by both of the two different types of lighting devices.

22. Method, according to claim 21, wherein one of the power components is pulse width modulated (PWM).

23. Method, according to claim 22, wherein another of the power components is selected from the group comprising DC, AC and PWM.

24. Method, according to claim 21, wherein at least one of the two different types of lighting devices is an LED.

25. Dimmer for controlling light intensity of LEDs and incandescent bulbs connected to a common power bus comprising:

means for providing a composite signal on the power bus comprising a first component (V1) and a second component (V2), wherein;

the first component is PWM and controls the intensity (L) of the LEDs in direct proportion to the PWM duty cycle (D), and contributes to the intensity of the incandescent bulbs; and

the second component is selected from the group comprising DC, AC and PWM, and is selected such that the second component contributes to the intensity of the incandescent bulbs and does not contribute to the intensity of the LEDs.