| 摘要 |
An SMPS(Switching Mode Power Supply) is provided to prevent damage and load of a device due to overvoltage or undervoltage by using an overvoltage protection circuit and an undervoltage protection circuit. A primary circuit of an SMPS includes a power supply unit, a first rectifying/smoothing unit, a switching unit(130), a voltage detector(140), an underground protection unit(150), and an overvoltage protection unit(160). An AC voltage is inputted to the power supply unit. A first rectifying/smoothing unit rectifies and smoothes the AC voltage into the DC voltage. The switching unit supplies the power to the secondary circuit by the switching operation. The voltage detector detects the voltage supplied from the first rectifying/smoothing unit. If the voltage detected by the voltage detector is less than the first voltage, the undervoltage protection unit controls the switching unit to block the voltage output to the secondary side circuit.
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