| 摘要 |
PURPOSE:To protect an output transistor by detecting the excessive voltage of an input signal to an image output amplifier and controlling consumed power of output transistor of the image output amplifier during the input period of the excessive voltage. CONSTITUTION:When the input signal inputted in an input terminal indicates an excessive voltage, the voltage is compared with the voltage level VTH set in the input terminal of a comparator 4. As the result, the comparator 4 outputs a negative pulse signal in the period exceeding VTH. The pulse signal is inputted in an integrating circuit 5, smoothed, and controls a stabilized electric source. The stabilized electric source is composed of an error amplifier 3 and an output transistor Tr Q4 of the voltage source to provide the voltage VC to a load resistance RL of Tr Q1 and a collector of Tr Q2. In such a case, when the input signal indicates an excessive voltage level, the voltage VC is decreased to regulate the consumption of power of the output transistor. In case that unusual period of image signal lasts decrease of VC grows bigger to make a sufficient protection of output transistor.
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