DIMMABLE LIGHT GENERATING DEVICE

• US 20100270936A1
• Filed: 12/12/2008
• Published: 10/28/2010
• Est. Priority Date: 12/14/2007
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Ettes, Wilhelmus, Heeringa, Schelte, Dijkstra, Jacob, Bremer, Petrus Johannes
• Granted Patent: US 8,487,540 B2
• Time in Patent Office: Days
• US Class Current: 315/219
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations

Abstract

A wake-up lighting device is described, comprising a gas discharge lamp (10) and a lamp driver (1; 2) comprising a power source (100) capable of generating spaced-apart current bursts (51) of alternating lamp current (I). The wake-up lighting device is capable of operating in an off-mode in which no lamp current is generated, and is adapted to switch from its off-mode to a wake-up mode in which the power source (100) operates to:—initially generate an alternating lamp current (I) with a minimum duty cycle value (ΔT) and a reduced current amplitude (IR) close to zero;—subsequently gradually increase the current amplitude while keeping the duty cycle (Δ) constant at the minimum duty cycle value (ΔT), until the current amplitude reaches a nominal current amplitude (IM);—subsequently gradually increase the duty cycle (Δ) while keeping the current amplitude constant at the nominal current amplitude (IM).

Claims

1. Method of driving a gas discharge lamp (10) with a variable light level in a range between nominal light output level (L_M) and minimum light output level, comprising the steps of:

generating an alternating lamp current (I) with a constant current amplitude;

when generating the nominal light output level (L_M), constantly supplying the lamp (10) with the alternating lamp current (I) having a nominal current amplitude (I_M);

when generating light having a light output level in a first range below said nominal light output level (L_M), supplying the lamp (10) with spaced apart current bursts (51) having a burst duration Tc and a burst repetition period T, wherein in each current burst the lamp is constantly supplied with the alternating lamp current (I) having the nominal current amplitude (I_M), and wherein in the intervals between successive current bursts substantially no current is supplied to the lamp, and wherein the light output level is varied by varying the burst duty cycle (Δ

) defined as Δ

=Tc/T within a range between 100% and a minimum burst duty cycle value (Δ

_T);

when generating light having a light output level in a second range below said first range, supplying the lamp (10) with spaced apart current bursts (51), wherein in each current burst the lamp is constantly supplied with the alternating lamp current (I) having a reduced current amplitude (I_R) lower than the nominal current amplitude (I_M), and wherein in the intervals between successive current bursts substantially no current is supplied to the lamp, and wherein the light output level is varied by varying the reduced current amplitude (I_R) within a range between zero and the nominal current amplitude (I_M) while keeping the burst duty cycle (Δ

) constant at said minimum burst duty cycle value (Δ

^T).

2. Method according to claim 1, wherein said minimum burst duty cycle value (Δ

_T) is in the order of 1%, or even lower, for instance 0.5%.

3. Method according to claim 1, for gradually increasing the light output level from zero to the nominal light output level, comprising the steps of:

initially supplying the lamp (10) with spaced apart current bursts (51) having said predetermined minimum burst duty cycle value (Δ

_T), wherein in each current burst the lamp is constantly supplied with the alternating lamp current (I) having the reduced current amplitude (I_R) close to zero;

subsequently, while keeping the burst duty cycle (Δ

) constant at said minimum burst duty cycle value (Δ

_T), gradually increasing the light output level by gradually increasing the reduced current amplitude until the current amplitude reaches the nominal current amplitude (I_M);

subsequently, while keeping the current amplitude constant at said nominal current amplitude (I_M), gradually increasing the light output level further by gradually increasing the burst duty cycle (Δ

).

4. Method according to claim 1, wherein the burst repetition period is in the order of about 100 Hz.

5. Method according to claim 1, wherein the alternating lamp current has a constant current frequency, this frequency preferably being in the order of about 100 kHz.

6. Method according to claim 1, wherein the alternating lamp current has a constant current duty cycle equal to 50%.

7. Driver (1) for driving a gas discharge lamp (10), comprising a main power source (100) capable of generating lamp current (I) in spaced apart current bursts (51) having a burst duration Tc and a burst repetition frequency 1/T, wherein in each current burst the lamp current is an alternating current having a constant current frequency higher than the burst repetition frequency, a constant current amplitude, and preferably a constant current duty cycle equal to 50%;

the driver being capable of varying the burst duty cycle (Δ

) defined as Δ

=Tc/T within a range between 100% and a minimum burst duty cycle value (Δ

_T) while keeping the current amplitude constant at a nominal current amplitude value (I_M);

and the driver being capable of varying the current amplitude within a range between zero and the nominal current amplitude (I_M) while keeping the burst duty cycle (Δ

) constant at said minimum burst duty cycle value (Δ

_T).

8. Driver according to claim 7, adapted to perform the method of driving a gas discharge lamp (10) with a variable light level in a range between nominal light output level LM and minimum light output level comprising the steps of:

generating an alternating lamp current (I) with a constant current amplitude;

when generating the nominal light output level (L_M), constantly supplying the lamp (10) with the alternating lamp current (I) having a nominal current amplitude (I_M);

when generating light having a light output level in a first range below said nominal light output level (L_M), supplying the lamp (10) with spaced apart current bursts (51) having a burst duration Tc and a burst repetition period T, wherein in each current burst the lamp is constantly supplied with the alternating lamp current (I) having the nominal current amplitude (L_M), and wherein in the intervals between successive current bursts substantially no current is supplied to the lamp, and wherein the light output level is varied by varying the burst duty cycle (Δ

) defined as Δ

=Tc/T within a range between 100% and a minimum burst duty cycle value (Δ

_T);

when generating light having a light output level in a second range below said first range, supplying the lamp (10) with spaced apart current bursts (51), wherein in each current burst the lamp is constantly supplied with the alternating lamp current (I) having a reduced current amplitude (I_R) lower than the nominal current amplitude (I_M), and wherein in the intervals between successive current bursts substantially no current is supplied to the lamp, and wherein the light output level is varied by varying the reduced current amplitude (I_R) within a range between zero and the nominal current amplitude (I_M) while keeping the burst duty cycle (Δ

) constant at said minimum burst duty cycle value (Δ

_T).

9. Driver according to claim 7, further comprising electrode-heating power sources (30, 40) adapted for providing a constant filament heating current or a constant filament heating voltage, independent of the burst duty cycle (Δ

) and independent of the current amplitude.

10. Driver according to claim 7, comprising:

a DC voltage source (106);

first and second DC power output lines (107, 108) connected to respective output terminals of the DC voltage source (106);

a first bridge leg (110) including a first series arrangement of two controllable switches (111, 112) connected between said first and second DC power lines (107, 108) with a first bridge output node (Δ

) between these two switches;

a second bridge leg (120) including a second series arrangement of two controllable switches (121, 122) connected between said first and second DC power lines (107, 108) with a second bridge output node (B) between these two switches;

a bridge diagonal (130) connected between said two output nodes (A, B);

a controller (90) for controlling the switching operation of said switches.

11. Driver according to claim 10, wherein the controller is adapted to control the switches in such a way that each switch (111, 112, 121, 122) is continuously alternated between a conductive state and a non-conductive state at a switching frequency equal to the current frequency, wherein the two switches (111, 112) of the first bridge leg (110) are always switched with a mutual phase difference of 180°

, wherein the two switches (121, 122) of the second bridge leg (120) are always switched with a mutual phase difference of 180°

;

the controller being adapted to selectively set the phase difference (Δ

φ

) between the first bridge leg (110) and the second bridge leg (120) in a range between 0° and

180°

.

12. Driver according to claim 10, wherein the controller is adapted, in the intervals between successive current bursts, to set said phase difference (Δ

φ

) to be equal to 0°

in order to supply substantially no current to the lamp.

13. Driver according to claim 10, wherein the controller is adapted, during a current burst, to set said phase difference (Δ

φ

) to be equal to 180°

in order to generate the alternating lamp current (I) having the nominal current amplitude (I_M).

14. Driver according to claim 10, wherein the controller is adapted, during a current burst, to set said phase difference (Δ

φ

) to have a value between 0° and

180°

in order to generate the alternating lamp current (I) having the reduced current amplitude (I_R).

15. Driver according to claim 10, wherein the bridge diagonal (130) comprises a series arrangement of lamp output terminals (101, 102) and inductive means (131, 132), with capacitive means 133, 134 arranged in parallel with said lamp output terminals (101, 102).

16. Driver according to claim 10, further comprising a coupling transformer (810), wherein the bridge diagonal (130) comprises the primary winding (811) of the coupling transformer (810), preferably in series with a DC decoupling capacitor (820), and wherein the lamp output terminals (101, 102) are arranged in series with the secondary winding (812) of the coupling transformer (810).

17. Driver according to claim 10, for driving a hot cathode fluorescent lamp (10) of a type comprising a lamp tube (11) having an interior space (12) and two electrode filaments (13;

14) arranged within the interior space, each electrode filament (13;

14) being provided with two electrode terminals (15, 17;

16, 18) extending to the exterior beyond the lamp tube;

the driver further comprising;

at least one electrode-heating power source (30;

40) for providing electrode heating current to a lamp electrode filament (13;

14);

the electrode-heating power source (30;

40) having a first input terminal (33) coupled to a bridge output node (A;

8) for deriving input power from the main power source.

18. Driver according to claim 17, wherein the electrode-heating power source (30;

40) comprises a transformer (50;

60) having a primary winding (51;

61) connected to its first input terminal (33;

43) and having a secondary winding (52;

62) coupled to its heating output terminals (31, 32;

41, 42).

19. Driver according to claim 18, wherein said electrode-heating power source (30;

40) further comprises a capacitor (35;

45) arranged between said primary transformer winding (51;

61) and a reference potential.

20. Driver according to claim 18, wherein said electrode-heating power source (30;

40) further comprises a voltage regulator (71;

72) coupled between said secondary transformer winding (52;

62) and said heating output terminals (31, 32;

41, 42).

21. Wake-up lighting device comprising a gas discharge lamp (10) and a lamp driver (1;

2) comprising a power source (100) capable of generating spaced apart current bursts (51) of alternating lamp current (I), wherein the device is capable of operating in an off-mode in which no lamp current is generated, and wherein the device is adapted to switch from its off-mode to a wake-up mode in which the power source (100) operates to;

initially generate an alternating lamp current (I) with a minimum duty cycle value (Δ

_T) and a reduced current amplitude (I_R) close to zero;

subsequently gradually increase the current amplitude, while keeping the duty cycle (Δ

) constant at the minimum duty cycle value (Δ

_T), until the current amplitude reaches a nominal current amplitude (I_M);

subsequently gradually increase the duty cycle (Δ

) while keeping the current amplitude constant at the nominal current amplitude (I_M).

22. Wake-up lighting device according to claim 21, wherein the gas discharge lamp comprises a plurality of tube segments (911, 912, 913, 914) arranged substantially parallel to each other, the tube segments having an axial length, the number of tube segments being an even integer, each tube segment having an interior space, the tube segments being coupled to each other by transverse tube segments (931, 932, 933) so that the interior space of one tube segment always communicates with the interior space of at least one other tube segment;

the device further comprising an electrically conductive external auxiliary electrode (950;

960), arranged outside the tube segments (911, 912, 913, 914), having an axial extent corresponding to the axial length of the tube segments, being capacitively coupled to all tube segments, and being coupled to a reference voltage level.