| 摘要 |
PURPOSE:To block consecutive drive state of a drive signal of a light emitting means due to a fault by a DC block means and to prevent damages to the light emitting means and its drive system even when the runaway and the fault of a control means controlling an infrared-ray emitting means occur and the driving signal of the emitting means are consecutively in the driving condition by driving a drive means of an infrared-ray emitting means via the DC blocking means. CONSTITUTION:A CPU 6 outputs a pulse at a prescribed blinking pattern in response to the depression of a key switch 25. A charging current of a capacitor 3 flows to the capacitor 3 and the base-emitter of a transistor(TR) 5 by the pulse output, the TR 5 is conductive and an LED 2 is light emitted for this period. When the output impedance of the CPU 6 is small, the lighting period of the LED 2 depends on the time constant of a resistor 4 and a capacitor 3. Even if the output of the CPU 6 is in high level state consecutively due to runaway or a fault in the element, the period of the base current flowing to the TR 5 is limited through the provision of the capacitor 3 and the conducting period of the TR 5 is the same as the case with normal operation. Thus, the components of the light emitting circuit such as the LED 2 and the TR 5 are protected surely from damages. |
