Circuit device

• US 6,445,140 B2
• Filed: 06/18/2001
• Issued: 09/03/2002
• Est. Priority Date: 06/20/2000
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Beij, Marcel, Langeslag, Wilhelmus Hinderikus Maria, Buij, Arnold Willem, Hendrix, Machiel Antonius Martinus
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, THUY V
• Application Number:
  US09/883,428
• Publication Number:
  US 20020014856A1
• Time in Patent Office: 442 Days
• Field of Search: 315/209.R, 315/224, 315/244, 315/291, 315/360, 315/DIG.2, 315/DIG.4, 315/DIG.5, 315/DIG.7, 363/34, 363/37
• US Class Current: 315/291
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

A lamp is operated by means of a DC-AC converter provided with switches and generating an AC current at a high frequency. In each half period of the lamp current, the voltage across the lamp is reversed during an adjustable time interval. The lamp can be dimmed without instabilities by adjusting the time interval.

Claims

1. A circuit device for supplying an alternating current of frequency f to a lamp, which circuit device is provided with a DC-AC converter comprising

input terminals for connecting the circuit device to a supply voltage source supplying a DC voltage,

a first branch including a series arrangement of a first switching element and a second switching element,

a control circuit coupled to respective control electrodes of the switching elements for rendering the switching elements conducting and non-conducting,

a load branch shunting one of the switching elements and provided with a series arrangement of an inductive element and terminals for accommodating the lamp,

characterized in that the control circuit generates a control signal at a frequency f during operation of the lamp,

for rendering the first switching element, in each first half period of the control signal, successively conducting, non-conducting and conducting during, respectively, a first, a second and a third time interval, the second switching element always being conducting when the first switching element is non-conducting, and non-conducting when the first switching element is conducting, and

for rendering the second switching element, in each second half period of the control signal, successively conducting, non-conducting and conducting during, respectively, a fourth, a fifth and a sixth time interval, the first switching element always being conducting when the second switching element is non-conducting, and non-conducting when the second switching element is conducting, and in that the control circuit is further provided with a dimming circuit for setting the duration of the second and the fifth time interval.

2. A circuit device as claimed in claim 1, wherein the duration of the second time interval is equal to the duration of the fifth time interval.

3. A circuit device as claimed in claim 2, wherein the second and the fifth time interval can be adjusted in a range from zero to ⅙

T, where T is the duration of a period of the control signal.

4. A circuit device as claimed in claim 2, wherein the second and the fifth time interval can be adjusted in a range from ⅙

T to ½

T.

5. A circuit device as claimed in claim 1, wherein Δ

t1/Δ

t3=1 and Δ

t4/Δ

t6=1 for each adjustable value of Δ

t2 and Δ

t5, where Δ

t1-Δ

t6 are, respectively, the durations of the first to the sixth time interval.

6. A circuit device as claimed in claim 1, wherein the dimming circuit is also provided with a circuit part for setting the point in time at which the second time interval begins within each first half period of the control signal, and for setting the point in time at which the fifth time interval begins within each second half period of the control signal.