Power switch circuit

A power switch circuit, comprising:

• a first transistor, wherein a first source/drain terminal of the first transistor receives a first supply voltage, a second source/drain terminal of the first transistor is connected with a node z, a gate terminal of the first transistor receives a second supply voltage, a body terminal of the first transistor is connected with the node z, and an output signal is outputted from the node z;
• a second transistor, wherein a first source/drain terminal of the second transistor receives the second supply voltage, a second source/drain terminal of the second transistor is connected with the node z, a gate terminal of the second transistor receives the first supply voltage, and a body terminal of the second transistor is connected with the node z;
• a third transistor, wherein a first source/drain terminal of the third transistor receives a bias voltage, a second source/drain terminal of the third transistor is connected with the node z, a gate terminal of the third transistor receives a shifted signal, and a body terminal of the third transistor is connected with the node z;
• an automatic selection circuit receiving the first supply voltage and the second supply voltage and generating an output voltage, wherein if the first supply voltage is lower than the second supply voltage, the first supply voltage is selected as the output voltage, wherein if the first supply voltage is higher than the second supply voltage, the second supply voltage is selected as the output voltage;
• and
• a level shifter for converting a control signal into the shifted signal according to the control signal and the output voltage of the automatic selection circuit.