| 摘要 |
PURPOSE:To relieve switching elements of stresses and to reduce noises by preferring operating phase control to operating frequency control for switching elements which are connected to a load circuit in the event that an abnormality such as overcurrent or overvoltage arises. CONSTITUTION:A load circuit, including a resonance circuit of an inductor L and a capacitor C and also including an electric discharge lamp 2, is connected to two pairs of series switching elements, S1 and S2, S3 and S4, which are in parallel with an AC power source E, and the elements S1-S4 have their operating frequencies and operating phases controlled via a control circuit. If the electric discharge lamp 2 has its load impedance sharply varied at the end of its life and an overvoltage or overcurrent is generated, the circuit 1 prefers the operating phase control to the operating frequency control and turns the elements S1-S4 on and off. Therefore, even if the load current or the like is sharply increased by the abrupt change in load impedance, the time required for the load circuit to be connected to the power source is reduced and increase in the load current or the like is limited, so the switching elements are relieved of stresses. Also, waveform distortions, and thus noises, are reduced. |
