| 摘要 |
<p>PURPOSE: A power supply for a LED(Light Emitting Diode) traffic signal lamp is provided to control the luminance of the LED traffic signal by coping with the form of the input voltage and outputting two kinds of constant voltages. CONSTITUTION: A protection circuit part(110) prevents the excess current and/or the overvoltage included in an AC power source. An on/off control signal generating part(200) generates on/off control signal according to the comparison result between an AC voltage and a reference voltage. An output voltage control part(190) controls the output voltage of the output terminal. A second voltage feedback part(180) comprises a second photo diode. The intensity of radiation of the second photo diode is varied according to the change of a current outputted to the second side of a transformer of a power supply unit. A PWM(Pulse Width Modulation) signal generating part(140) controls the duty ratio of a PWM signal according to the change of the intensity of radiation of the second photo diode.</p> |
