| Summary: | 碩士 === 國立暨南國際大學 === 電機工程學系 === 93 === In this thesis, we have designed an automatic photo-power control circuit which can effectively prevent the power variation owing to the heat effect as a result of threshold current variation in photoelectric devices. For a 10 mW laser operating under direct-current case, the controlled temperature range can be achieved is 40℃. Under the case of pulse width modulation, the controlled temperature range increases as the duty cycle decreases. For a 20% duty cycle, the controlled temperature range can reach up to 50℃ and 75 KHz operating frequency can be attained, which meets the requirement of backlighting in liquid crystal display. For the case of sine wave modulation, a maximum100 KHz operating frequency can be achieved. When pulse in accompanied with sine wave modulation, a 1 K plus 10 KHz operating frequency can be achieved. In combining with plastic optical fiber, the designed automatic photo-power control circuit can find application in short distance communication.
The content of this thesis includes the measurements of photoelectric device characteristics, the determination of optimum operating point of the photoelectric device, the design and applications of the operational amplifier for pulse, sine and pulse plus sine wave modulations. The design flow described in this thesis can also be used for light emitting diodes, as well as other light sources with 5 mW, and 20 mW light power.
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