Power safety system
A power safety system includes a first MOS, a second MOS, a switch and a body controller. The first MOS is connected between a power input and a power output. The second MOSFET is connected between the power output and a charging output. The switch has an end connected to the body of the first MOS, and the opposite end switched between the source and the drain of the first MOS. A body controller controls the switch according to the voltage at the power input and the voltage at the power output, to connect the body of the first MOS to the source or the drain of the first MOS. By switching the switch, the first MOS will have a parasitic diode effective to prevent a reverse current from the power output to the power input.
1. A power safety system, comprising:
a power input to be connected with a power supply;
a power output to be connected to a load system;
a first MOS transistor formed on a body, connected between the power input and the power output, and having a source, a drain, and a gate;
an amplifier connected to the power input, the power output, and the gate of the first MOS transistor, and configured to determine a first control signal according to a voltage at the power input and a voltage at the power output, to be applied to the gate of the first MOS transistor;
a charging output end to be connected to a battery;
a second MOS transistor connected between the power output and the charging output, and having a gate;
a power management device connected to the charging output and the gate of the second MOS transistor, and configured to monitor a voltage at the charging output to determine a second control signal to be applied to the gate of the second MOS transistor, thereby controlling a charging current flowing to the charging output;
a body controller connected to the power input, the power output, and the body of the first MOS transistor, and configured to determine a third control signal according to the voltage at the power input and the voltage at the power output; and
a switch having an end connected to the body of the first MOS transistor and an opposite end to be switched between the source and the drain of the first MOS transistor in response to the third control signal.
2. The power safety system of claim 1 , wherein the first MOS transistor comprises a PMOS.
3. The power safety system of claim 1 , wherein the amplifier is a transconductive amplifier configured to provide a current as the first control signal according to a difference between the voltage at the power input and the voltage at the power output.
4. The power safety system of claim 1 , wherein the second MOS transistor comprises a PMOS.
5. The power safety system of claim 1 , wherein the second MOS transistor has a parasitic diode having an anode and a cathode connected respectively to the charging output and the power output.
6. The power safety system of claim 1 , wherein the first MOS transistor has a first parasitic diode having an anode and a cathode connected respectively to the power output and the power input when the third control signal is at a first state, and a second parasitic diode having an anode and a cathode connected respectively to the power input and the power output when the third control signal is at a second state.
7. A method for a power safety system which includes a first MOS transistor connected between a power input and a power output, and a second MOS transistor connected between the power output and a charging output, the method comprising:
(A) monitoring a voltage at the power input and a voltage at the power output to determine a first control signal to be applied to a gate of the first MOS transistor;
(B) monitoring a voltage at the charging output to determine a second control signal to be applied to a gate of the second MOS transistor, thereby controlling a charging current flowing to the charging output; and
(C) monitoring the voltage at the power input and the voltage at the power output to determine a third control signal, wherein the first MOS transistor has a first parasitic diode having an anode and a cathode connected respectively to the power output and the power input when the third control signal is at a first state, and a second parasitic diode having an anode and a cathode connected respectively to the power input and the power output when the third control signal is at a second state.
8. The method of claim 7 , wherein the step A comprises:
comparing the voltage at the power input with the voltage at the power output; and
controlling the first MOS transistor with the first control signal when a difference between the voltage at the power input and the voltage at the power output is smaller than a preset value, so as to maintain the difference between the voltage at the power output and the voltage at the power input at a constant value.
9. The method of claim 7 , wherein the step B comprises:
comparing the voltage at the charging output with a preset value; and
turning off the second MOS transistor with the second control signal when the voltage at the charging output exceeds the preset value.
10. The method of claim 7 , wherein the step C comprises:
connecting a body of the first MOS transistor to a drain of the first MOS transistor when the third control signal is at a first state; and
connecting the body of the first MOS transistor to a source of the first MOS transistor when the third control signal is at a second state.