| 摘要 |
<p>A step-down chopper circuit (15) has a switching element (151) connected in series with a light emitting element (41) between a pair of input terminals (11) and a control circuit (152) that carries out on and off control of the switching element (151). A detection circuit (16) comprises a comparator (161) that compares a detected voltage, which is the output voltage from a rectifier (14), with a threshold voltage (Vth) that is greater than the minimum voltage at which the control circuit (152) operates. When the detected voltage exceeds the threshold voltage (Vth), an H level signal is output. An isolating circuit (17) is inserted into the power supply pathway to the control circuit (152), and when the output of the comparator (161) is the H level, the same is turned on; when the output of the comparator (161) is an L level, the same is turned off, and the switching element (151) is fixed to off.</p> |
