Power latch
First Claim
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1. A circuit that connects the higher voltage of two power supplies to an output, the circuit comprising:
- a first transistor with its source connected to a first power supply and its gate to a second power supply;
a second transistor with its source connected to the second power supply and its gate to the first power supply;
cross coupled first and second inverters, the first inverter input connected to the first transistor drain and the second inverter input connected to the second transistor drain;
the first inverter powered by the second power supply and the second inverter powered by the first power supply;
the input of the first inverter connected to the output of the second inverter, and the input of the second inverter connected to the output of the first inverter;
a third transistor with its gate connected to the drain of the second transistor, its source connected to the first power supply and its drain connected to the output voltage; and
a fourth transistor with its gate connected to the first transistor drain, its source connected to the second power supply and its drain connected to the output.
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Abstract
A circuit that automatically, seamlessly connects the higher (or the lower) of two power supplies to an output is described. The circuit does not incur a one diode drop when the two power supplies are at about the same voltage levels, and the unused power supply draws no stand-by current. Cross coupled transistor and cross coupled inverters are employed.
16 Citations
4 Claims
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1. A circuit that connects the higher voltage of two power supplies to an output, the circuit comprising:
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a first transistor with its source connected to a first power supply and its gate to a second power supply; a second transistor with its source connected to the second power supply and its gate to the first power supply; cross coupled first and second inverters, the first inverter input connected to the first transistor drain and the second inverter input connected to the second transistor drain;
the first inverter powered by the second power supply and the second inverter powered by the first power supply;
the input of the first inverter connected to the output of the second inverter, and the input of the second inverter connected to the output of the first inverter;a third transistor with its gate connected to the drain of the second transistor, its source connected to the first power supply and its drain connected to the output voltage; and
a fourth transistor with its gate connected to the first transistor drain, its source connected to the second power supply and its drain connected to the output. - View Dependent Claims (2)
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3. A method for connecting the higher of two power supplies to an output voltage, the method comprising:
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connecting a first transistor source to a first power supply and its gate to a second power supply; connecting a second transistor source to the second power supply and its gate to the first power supply; cross-coupling first and second inverters, the first inverter input connected to the first transistor drain and the second inverter input connected to the second transistor drain;
the first inverter powered by the second power supply and the second inverter powered by the first power supply;
the input of the first inverter connected to the output of the second inverter, and the input of the second inverter connected to the output of the first inverter;connecting a third transistor gate to the drain of the second transistor, its source connected to the first power supply and its drain connected to the output voltage; and
connecting a fourth transistor gate to the first transistor drain, its source connected to the second power supply and its drain connected to the output voltage. - View Dependent Claims (4)
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Specification