| 摘要 |
PROBLEM TO BE SOLVED: To provide a lighting deuce capable of preventing stress applied to a switching means and the consumption of unnecessary electric power even when a filament capacitor exists. SOLUTION: A fluorescent lamp FL is started and lit by converting into high frequency AC with an inverter circuit 3. Lamp current is detected with an input winding CT1a of a current transformer CT1, the switching of a transistor Q1 is controlled based on the variation of the lamp current, and the output of the fluorescent lamp FL is kept constant. In the state that the fluorescent lamp FL is removed, filaments FL1, FL2 are removed, and a circuit is opened. Since current does not flow to the input winding CT1a of the current transformer CT1, voltage is not induced in an output winding CT1b, and current does not flow. Since the base current does not flow in the transistor Q1, the transistor Q1 is not oscillated, and the oscillation of the inverter circuit 3 stops. |
