DC-AC converter for igniting and supplying a gas discharge lamp

A DC-AC converter for igniting and supplying a gas discharge lamp comprises first and second input terminals for connection to a source of DC voltage;

• a transformer having a primary winding, a first secondary winding a second secondary winding;
• first, second, third and fourth controlled semiconductor switching elements each having a first electrode, a second electrode and a control electrode;
• a captive voltage divider having a first and a second capacitor;
• first means for connecting the first and second semiconductor switching elements in a first series circuit across said first and second input terminals;
• second means for connecting a first end of a load circuit to a junction point between the first and second semiconductor switching elements and further connecting a second end of the load circuit to the second input terminal via a current sensor resistor, the load circuit comprising a third capacitor, an induction coil and a gas discharge lamp;
• third means for connecting a first end of the capacitive voltage divider to a junction point between the first and second semiconductor switching elements and for connecting a second end of the capacitive voltage divider to the second input terminal;
• fourth means for connecting the second capacitor in a parallel circuit with the primary winding via a first resistor;
• fifth means for connecting a first diode and the third semiconductor switching element across the primary winding;
• sixth means for connecting the current sensor resistor to a first resistive voltage divider comprising a second and a third resistor via a fourth resistor, and for connecting the control electrode of the third semiconductor switching element to a junction point between the second and third resistor;
• seventh means for connecting a second resistive voltage divider comprising a fifth and a sixth resistor across the lamp;
• and eighth means for connecting the first electrode of the fourth semiconductor switching element to one end of the first resistive divider via a second diode and connecting the source electrode of the fourth semiconductor element to the other end of the first resistive voltage divider, and further connecting the control electrode of the fourth switching element to a junction point between the fifth and sixth resistors, of the second resistive voltage divider via a third diode of a voltage rectifier, the voltage rectifier comprising the third diode and a fourth capacitor.