| 摘要 |
PURPOSE:To make possible efficient selection of a lighting circuit by determining the kind of power source through comparison of a reference voltage with a source voltage, and switching a highly efficient lighting circuit to a normal current dimming type circuit or vice versa. CONSTITUTION:In an electric discharge lamp lighting circuit using an inverter circuit, a reference voltage Vref from a PWM-IC used in current dimming method is compared with a source voltage Vin by a comparator IC, and when the voltage Vin is not greater than a predetermined value, the power source used is determined as being a battery power source, while when the voltage Vin is greater than the predetermined value the power source is determined as an AC power source through an AC adapter. When the power source is determined as being a battery, a transistor(TR)Q4 is turned off by the determination output of the comparator IC, the PWM=IC is turned off, a transistor TRQ3 is turned on, and the primary side of a high voltage circuit is grounded so that a lighting circuit of higher efficiency is automatically selected. Therefore, the battery with a limited capacity can be used over a long time. |
