US Patent 7541749 Current-mode resonant inverter circuit for discharge lamp

A highly stable current-mode resonant inverter circuit operates by detecting resonance current in the secondary side circuit. The inverter circuit comprises a step-up transformer with a secondary winding connected to a secondary side circuit with a capacitive component. The leakage inductance and the secondary winding and the capacitive component compose a series resonant circuit. The inverter circuit is configured to detect a current flowing through the secondary winding or capacitive component in the secondary side circuit, and determine a switching timing in response to the detected current. The determined switching timing allows the inverter circuit to oscillate self-excitedly at a resonance frequency of the series resonant circuit.