| 摘要 |
PURPOSE:To enable to shorten the rising time of the luminous flux or the like of a lamp by limiting the current reduction for maintaining the power constant in a low voltage range, i.e., large current range, thereby supplying the large current immediately after starting. CONSTITUTION:A clamping circuit which has a diode 11 is connected in parallel with a current detecting resistor 4 of a chopper circuit. In other words, the resistor 4 is clamped by the prescribed voltage value, thereby preventing the peak value of the detected voltage from rising so as not to shorten the ON time of a main transistor 5. Thus, the current value in a low voltage range increases, and the heating of the lamp 3 is accelerated. Since the transistor 5 might damage at a load shortcircuiting time, a current detector 14 made of a current transformer 13 is provided, the output current is dropped by the current detection output to protect the overcurrent. |
