| 摘要 |
PURPOSE: A protection circuit for an electric power source is provided to prevent the overvoltage from applying to the other circuits by using the switching unit operated by the clock signal having a predefined duty ratio. CONSTITUTION: The protection circuit comprises an input port to receive an electric power(VCC), an output port to apply the power to the target circuit, a control signal input port to receive the control signal used to control the power supply, and a switching unit to supply or to stop of the power supplying according to the control signal. The protection circuit includes the first switching transistor where the emitter and the collector are connected and the base is connected to the collector via the first capacitor and connected to the collector of the second switching transistor via a resistor and the first and second capacitors are grounded, and the emitter of the second switching transistor is grounded and the collector and the base are connected each other via a resistor and the base of the second switching transistor is connected to the control signal input port via a resistor. The protection circuit bypasses the applied input voltage to the output port when the voltage level of the base of the second switching transistor is high level, and isolates the applied input voltage when the voltage level of the base is low level.
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