Circuit Arrangement for Operation of a Discharge Lamp with a Switchable Tuned Capacitor
The invention relates to a circuit arrangement for operation of a discharge lamp (EL) with an inverter (INV) which generates a high-frequency alternating current from an input voltage and with a tuned circuit provided with at least one choke (L) and at least one tuned capacitor (C 3 , C 4 ), by means of which the lamp (EL) is supplied, whereby at least one tuned capacitor (C 4 ) is connected in series with a switch element (T 1 ) parallel to the lamp (EL). The resonance capacitance for control of the lamp can be varied by switching in or out the tuned capacitor. For example, the resonance capacitance can be increased for pre-heating and reduced on lamp operation.
1 . A circuit arrangement for operating a discharge lamp (EL), in particular a low-pressure discharge lamp, with an inverter (INV), which produces a high-frequency AC voltage from an input voltage (GL, C 1 ), with a resonant circuit (C 2 , L, C 3 , C 4 ), which comprises at least one inductor (L) and at least one resonant capacitor (C 3 , C 4 ), via which the lamp is supplied, characterized in that at least one resonant capacitor (C 4 ) is connected in series with a switching element (T 1 ) and in parallel with the lamp (EL).
2 . The circuit arrangement as claimed in claim 1 , characterized in that the switching element is a transistor (T 1 ), preferably a MOSFET.
3 . The circuit arrangement as claimed in claim 2 , characterized in that the cathode of a Zener diode (D 3 ) is connected to a control connection of the transistor and its anode is connected to a reference potential for the control voltage of the transistor.
4 . The circuit arrangement as claimed in claim 1 , characterized in that the discharge lamp (EL) has filaments which can be heated by current, and in that the current flows at least partially through the lamp filaments via the switchable resonant capacitor (C 4 ).
5 . The circuit arrangement as claimed in claim 4 , characterized in that the lamp filaments are bridged by diodes (D 1 , D 2 ) in such a way that the anode of a first diode (D 1 ) is connected to a connection of the switchable resonant capacitor, and the anode of a second diode (D 2 ) is connected to a connection of the switching element (T 1 ), and the cathodes of both diodes (D 1 , D 2 ) are connected to inverter-side connections of the filaments.
6 . The circuit arrangement as claimed in claim 1 , characterized in that the cathode of a diode (D 4 ) is connected to a positive supply potential of the inverter (INV) and its anode is connected to the switching element (T 1 ).
7 . The circuit arrangement as claimed in claim 2 , characterized in that the discharge lamp (EL) has filaments which can be heated by current, and in that the current flows at least partially through the lamp filaments via the switchable resonant capacitor (C 4 ).
8 . The circuit arrangement as claimed in claim 3 , characterized in that the discharge lamp (EL) has filaments which can be heated by current, and in that the current flows at least partially through the lamp filaments via the switchable resonant capacitor (C 4 ).
9 . The circuit arrangement as claimed in claim 2 , characterized in that the cathode of a diode (D 4 ) is connected to a positive supply potential of the inverter (INV) and its anode is connected to the switching element (T 1 ).
10 . The circuit arrangement as claimed in claim 3 , characterized in that the cathode of a diode (D 4 ) is connected to a positive supply potential of the inverter (INV) and its anode is connected to the switching element (T 1 ).
11 . The circuit arrangement as claimed in claim 4 , characterized in that the cathode of a diode (D 4 ) is connected to a positive supply potential of the inverter (INV) and its anode is connected to the switching element (T 1 ).
12 . The circuit arrangement as claimed in claim 5 , characterized in that the cathode of a diode (D 4 ) is connected to a positive supply potential of the inverter (INV) and its anode is connected to the switching element (T 1 ).