METHOD FOR OPERATING A FLUORESCENT LAMP

• US 20080150442A1
• Filed: 12/20/2007
• Published: 06/26/2008
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Infineon Technologies Austria Ag (Infineon Technologies AG)
• Original Assignee: Infineon Technologies Austria Ag (Infineon Technologies AG)
• Inventors: Feldtkeller, Martin
• Granted Patent: US 7,990,073 B2
• Time in Patent Office: Days
• US Class Current: 315/209R
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• 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 41/2981 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: H05B 41/36 Controlling

Abstract

A method for operating a fluorescent lamp which is connected to a series resonant circuit with a resonant circuit inductance and a resonant circuit capacitance. The method includes applying an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch which are alternately switched on and off on the basis of a frequency signal. A current flowing through the resonant circuit is monitored for the presence of a critical operating state. The switched-on times of the first and second switches are shortened in comparison to switched-on times which are predetermined by the frequency signal, upon detection of a critical operating state.

Claims

1. A method for operating a fluorescent lamp, which is connected to a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the method comprising:

applying an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch which are alternately switched on and off on the basis of a frequency signal;

monitoring of a current flowing through the resonant circuit, for the presence of a critical operating state; and

shortening of the switched-on times of the first and second switches in comparison to switched-on times which are predetermined by the frequency signal, on detection of a critical operating state.

2. The method of claim 1, wherein the first switch is switched off when the resonant circuit current reaches a first limit value when the first switch is switched on, and the second switch is switched off when the resonant circuit current reaches a second limit value when the second switch is switched on.

3. The method of claim 1, wherein the resonant circuit current is detected only at times, wherein one of the switches is switched off when the resonant circuit current which is a limit value when this particular switch is switched on, wherein a shortened switched-on time is determined for this switch and wherein the other switch is switched on in an immediately subsequently switched-on period for a time period which is between the shortened switched-on time and a switched-on time which is governed by the frequency signal.

4. The method of claim 3, wherein the time for which the other switch is switched on corresponds to the shortened time for which the first switch is switched on.

5. The method of claim 3, wherein the second switch is switched off when the resonant circuit current reaches the limit value when the second switch is switched on.

6. The method of claim 5, wherein a resonant circuit current is detected using a second measurement resistor which is connected between the second switch and a second supply potential.

7. A method for operating a fluorescent lamp, which is connected to a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the method comprising:

applying of an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch which are alternately switched on and off on the basis of a frequency signal; and

switching off at least one of the switches once a predetermined time period has elapsed after the presence of a predetermined phase angle of the resonant circuit current.

8. The method of claim 7, wherein the predetermined phase angle is a zero crossing of the resonant circuit current.

9. The method of claim 7, wherein the time for which the first switch is switched on is determined, and wherein the other switch is switched on, during a subsequent switched-on period, for a time period which is between the time for which the first switch is switched on and a switched-on time governed by the frequency signal.

10. The method of claim 9, wherein the time for which the other switch is switched on corresponds to the time for which the first switch is switched on.

11. The method of claim 7, wherein the predetermined time period is dependent on a peak value of the resonant circuit current and/or on the peak value of a time derivative of the resonant circuit current.

12. The method of claim 7, wherein the predetermined time period is dependent on an integral of the resonant circuit current over time.

13. A method for operating a fluorescent lamp, which is connected to a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the method comprising:

applying of an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch;

reducing excitation frequency for starting the fluorescent lamp; and

increasing the excitation frequency, at least temporarily, when the rate of change of a peak value of the resonant circuit current is greater than a predetermined threshold value.

14. The method of claim 13, wherein the excitation frequency is increased by immediately switching off the switch which is on at that time.

15. A method for operating a fluorescent lamp, which is connected to a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the method comprising:

applying of an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch;

reducing excitation frequency for starting the fluorescent lamp,

increasing the excitation frequency, at least temporarily, when a peak value of the resonant circuit current reaches a first threshold value;

causing a sudden phase change in the operation of the switches when the peak value of the resonant circuit current reaches a second threshold value;

ending the operation when the peak value of the resonant circuit current reaches a third threshold value; and

the first threshold value being less than the second threshold value, and the second threshold value being less than the third threshold value.

16. A method for operating a fluorescent lamp, which is connected to a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the method comprising:

applying of an excitation AC voltage at an excitation frequency to the series resonant circuit using a half bridge circuit, which has an output to which the series resonant circuit is coupled, and which has a first and a second switch which are alternately switched on and off on the basis of a frequency signal; and

determining a peak value of a current through the resonant circuit, and setting of the time for which the first and the second switch are switched on as a function of the frequency signal and the peak value.

17. The method of claim 16, wherein the time for which the first and second switches are switched on is shortened when the peak value exceeds the predetermined threshold value.

18. The method of claim 16, wherein the current through the half bridge is detected, and the half bridge is switched off when the half-bridge current exceeds a predetermined threshold value for a predetermined time period, with the predetermined time period assuming a first time period value within a time window after a switch-off flank of a drive signal for a switch which is on at that time in the half bridge, and otherwise assuming a second time period value which is shorter than the first time period value.