| 摘要 |
PURPOSE: A soft start unit without an external capacitor and a power supply having the same are provided to reduce cost of each component and miniaturize a size by using a soft start unit for performing a soft switching operation. CONSTITUTION: A soft start unit without an external capacitor includes an error amplifier(100), a voltage generator(400), a comparator(200), and a driver(300). The error amplifier(100) is used for sensing an output voltage and outputting a constant DC voltage. The voltage generator(400) is used for outputting periodically a first voltage and a second voltage during a first period and a second period in order to charge a second capacitor and output the voltage of the second capacitor. The comparator(200) is used for comparing a sensing voltage of a power MOS transistor to a lower voltage between an output voltage of the voltage generator and an output voltage of the error amplifier. The driver(300) is used for driving the power MOS transistor according to an output value of the comparator.
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