Circuit arrangement and method for operating at least one electric lamp
View Patent ↗A circuit arrangement for operating at least one electric lamp having an inverter has at least one first and one second bridge transistor arranged in series with one another, a first drive circuit for the first bridge transistor; a second drive circuit for the second bridge transistor; the and second drive circuits being designed to drive the first and second bridge transistors to switch alternately completely on and off during normal lamp operation; and at least one protective apparatus; the at least one protective apparatus being designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor which has just been switched off, above a predeterminable limit value, to drive the bridge transistor, which has just been completely switched on, such that it is no longer completely switched on. A related method is also described.
1. A circuit arrangement for operating at least one electric lamp (EL) having an inverter having at least one first bridge transistor (T 3 ) and one second bridge transistor (T 4 ) which are arranged in series with one another, a first drive circuit (AS 1 ) for the first bridge transistor (T 3 ); a second drive circuit (AS 2 ) for the second bridge transistor (T 4 ); the first drive circuit (AS 1 ) and the second drive circuit (AS 2 ) being designed to drive the first bridge transistor (T 3 ) and the second bridge transistor (T 4 ) such that they switch alternately completely on and off during normal operation of the lamp (EL); and at least one protective apparatus (TS 1 ; TS 2 ); characterized in that the at least one protective apparatus (TS 1 ; TS 2 ) is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the bridge transistor (T 4 ; T 3 ), which has just been completely switched on, of the series circuit such that it is no longer completely switched on.
2. The circuit arrangement as claimed in claim 1 , characterized in that the at least one protective apparatus (TS 1 ; TS 2 ) is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the bridge transistor (T 4 ; T 3 ), which has just been completely switched on, of the series circuit such that it is operated in the linear range.
3. The circuit arrangement as claimed in claim 1 , characterized in that the at least one protective apparatus (TS 1 ; TS 2 ) is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the bridge transistor (T 4 ; T 3 ), which has just been completely switched on, of the series circuit such that it is switched off.
4. The circuit arrangement as claimed in claim 1 , characterized in that it is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the two bridge transistors (T 3 , T 4 ) such that they remain switched off, at least over a predeterminable period of time, in particular until the reference voltage has again fallen below the predeterminable limit value.
5. The circuit arrangement as claimed in claim 1 , characterized in that it comprises a first protective apparatus (TS 1 ) and a second protective apparatus (TS 2 ), the first protective apparatus (TS 1 ) being designed to switch the second bridge transistor (T 4 ) off if a first reference voltage, which is correlated with the voltage present at the first bridge transistor (T 3 ), exceeds a predeterminable limit value, and the second protective apparatus (TS 2 ) being designed to switch the first bridge transistor (T 3 ) off if a second reference voltage, which is correlated with the voltage present at the second bridge transistor (T 4 ), exceeds a predeterminable limit value.
6. The circuit arrangement as claimed in claim 1 , characterized in that each bridge transistor (T 3 ; T 4 ) has a control terminal, the at least one protective apparatus (TS 1 ; TS 2 ) being coupled between the drive circuit (AS 1 ; AS 2 ) and the control terminal of the associated bridge transistor (T 3 ; T 4 ).
7. The circuit arrangement as claimed in claim 6 , characterized in that each bridge transistor (T 3 ; T 4 ) has a reference terminal, the at least one protective apparatus (TS 1 ; TS 2 ) being arranged in parallel with the control terminal-reference terminal path of the associated bridge transistor (T 3 ; T 4 ) and being designed to short-circuit the control terminal-reference terminal path of the associated bridge transistor (T 3 ; T 4 ) for disconnection purposes.
8. The circuit arrangement as claimed in claim 1 , characterized in that the predeterminable limit value is less than or equal to the maximum permissible reverse voltage of a bridge transistor (T 3 ; T 4 ).
9. The circuit arrangement as claimed in claim 1 , characterized in that the respective reference voltage corresponds to the voltage across the switched-off bridge transistor (T 3 ; T 4 ).
10. The circuit arrangement as claimed in claim 1 , characterized in that the respective reference voltage corresponds to the sum of the following voltages: the voltage across the switched-off bridge transistor (T 3 ; T 4 ); and the voltage at the output of the drive circuit (AS 1 ; AS 2 ) of the switched-on bridge transistor (T 3 ; T 4 ).
11. The circuit arrangement as claimed in claim 1 , characterized in that the protective apparatus (TS 1 ; TS 2 ) is designed to leave the associated bridge transistor (T 3 ; T 4 ) switched off until the value for the reference voltage has again fallen below the predeterminable limit value.
12. The circuit arrangement as claimed in claim 2 , characterized in that it is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the two bridge transistors (T 3 , T 4 ) such that they remain switched off, at least over a predeterminable period of time, in particular until the reference voltage has again fallen below the predeterminable limit value.
13. The circuit arrangement as claimed in claim 3 , characterized in that it is designed, in the case of a value for a reference voltage, which is correlated with the voltage across the bridge transistor (T 3 ; T 4 ) which has just been switched off, above a predeterminable limit value, to drive the two bridge transistors (T 3 , T 4 ) such that they remain switched off, at least over a predeterminable period of time, in particular until the reference voltage has again fallen below the predeterminable limit value.
14. The circuit arrangement as claimed in claim 2 , characterized in that it comprises a first protective apparatus (TS 1 ) and a second protective apparatus (TS 2 ), the first protective apparatus (TS 1 ) being designed to switch the second bridge transistor (T 4 ) off if a first reference voltage, which is correlated with the voltage present at the first bridge transistor (T 3 ), exceeds a predeterminable limit value, and the second protective apparatus (TS 2 ) being designed to switch the first bridge transistor (T 3 ) off if a second reference voltage, which is correlated with the voltage present at the second bridge transistor (T 4 ), exceeds a predeterminable limit value.
15. The circuit arrangement as claimed in claim 3 , characterized in that it comprises a first protective apparatus (TS 1 ) and a second protective apparatus (TS 2 ), the first protective apparatus (TS 1 ) being designed to switch the second bridge transistor (T 4 ) off if a first reference voltage, which is correlated with the voltage present at the first bridge transistor (T 3 ), exceeds a predeterminable limit value, and the second protective apparatus (TS 2 ) being designed to switch the first bridge transistor (T 3 ) off if a second reference voltage, which is correlated with the voltage present at the second bridge transistor (T 4 ), exceeds a predeterminable limit value.
16. The circuit arrangement as claimed in claim 4 , characterized in that it comprises a first protective apparatus (TS 1 ) and a second protective apparatus (TS 2 ), the first protective apparatus (TS 1 ) being designed to switch the second bridge transistor (T 4 ) off if a first reference voltage, which is correlated with the voltage present at the first bridge transistor (T 3 ), exceeds a predeterminable limit value, and the second protective apparatus (TS 2 ) being designed to switch the first bridge transistor (T 3 ) off if a second reference voltage, which is correlated with the voltage present at the second bridge transistor (T 4 ), exceeds a predeterminable limit value.
17. The circuit arrangement as claimed in claim 2 characterized in that each bridge transistor (T 3 ; T 4 ) has a control terminal, the at least one protective apparatus (TS 1 ; TS 2 ) being coupled between the drive circuit (AS 1 ; AS 2 ) and the control terminal of the associated bridge transistor (T 3 ; T 4 ).
18. The circuit arrangement as claimed in claim 3 characterized in that each bridge transistor (T 3 ; T 4 ) has a control terminal, the at least one protective apparatus (TS 1 ; TS 2 ) being coupled between the drive circuit (AS 1 ; AS 2 ) and the control terminal of the associated bridge transistor (T 3 ; T 4 ).
19. The circuit arrangement as claimed in claim 4 , characterized in that each bridge transistor (T 3 ; T 4 ) has a control terminal, the at least one protective apparatus (TS 1 ; TS 2 ) being coupled between the drive circuit (AS 1 ; AS 2 ) and the control terminal of the associated bridge transistor (T 3 ; T 4 ).