Voltage selector circuit

Abstract

This application provides a voltage selection circuit that, by controlling the switching on and off of a first P-type transistor and a second P-type transistor, enables the output of a first voltage or a second voltage as the maximum voltage at the voltage output node. This voltage selection circuit does not require special threshold voltages for the first and second P-type transistors, and even under high load current, the voltage output at the voltage output node will not experience threshold voltage drop issues, allowing for precise output of either the first or second voltage as the maximum voltage.

Claims

1. A voltage selection circuit, comprising: A voltage comparator has a first terminal connected to a first voltage, a second terminal connected to a second voltage, and an output terminal outputting a comparison signal corresponding to the comparison result of the first voltage and the second voltage; a first inverter has its input terminal connected to the output terminal of the voltage comparator to receive the comparison signal, and its output terminal outputting a first control signal corresponding to the inverse of the comparison signal; a second inverter has its input terminal connected to the output terminal of the first inverter, and its output terminal outputting a second control signal corresponding to the inverse of the first control signal; a first N-type transistor is controlled by the first control signal, and the control terminal of the first N-type transistor is connected to the output terminal of the first inverter. The input terminal is grounded and the output terminal is connected to a first node; a second N-type transistor, controlled by the second control signal, has its control terminal connected to the output terminal of the second inverter, its input terminal grounded, and its output terminal connected to a second node; a first P-type transistor, its control terminal connected to the first node, its input terminal connected to the first voltage, and its output terminal connected to a voltage output node; a second P-type transistor, its control terminal connected to the second node, its input terminal connected to the second voltage, and its output terminal connected to the voltage output node; a third P-type transistor, its control terminal connected to the first node, its input terminal connected to the voltage of the voltage output node, and its output terminal connected to the second node; And a fourth P-type transistor, whose control terminal is connected to the second node, whose input terminal is connected to the voltage of the voltage output node, and whose output terminal is connected to the first node.

2. The voltage selection circuit as described in claim 1, wherein when the first voltage is greater than the second voltage or the second voltage is not present, the first N-type transistor and the first P-type transistor are turned on, the second N-type transistor and the second P-type transistor are turned off, and the voltage output node outputs the first voltage.

3. The voltage selection circuit as described in claim 1, wherein when the second voltage is greater than the first voltage or the first voltage is not present, the second N-type transistor and the second P-type transistor are turned on, the first N-type transistor and the first P-type transistor are turned off, and the voltage output node outputs the second voltage.

4. The voltage selection circuit as described in claim 3, wherein: The third P-type transistor is used to pull up the voltage of the second node to the voltage of the voltage output node when the first N-type transistor is turned on; And the fourth P-type transistor is used to pull up the voltage of the first node to the voltage of the voltage output node when the second N-type transistor is turned on.

5. The voltage selection circuit as claimed in claim 1, wherein the first inverter is powered by the first voltage and the second inverter is powered by the voltage of the voltage output node.

6. The voltage selection circuit as described in claim 1, wherein the voltage comparator comprises: A reference current source; A third type N transistor, whose input terminal is grounded, and whose output terminal is connected to the control terminal and the reference current source; A fourth N-type transistor, whose input terminal is grounded and whose control terminal is connected to the control terminal of the third N-type transistor; a fifth P-type transistor, whose input terminal is connected to the first voltage and whose output terminal is connected to the control terminal and also connected to the output terminal of the fourth N-type transistor; and a sixth P-type transistor, whose input terminal is connected to the first voltage and whose control terminal is connected to the control terminal of the fifth P-type transistor.

7. The voltage selection circuit as described in claim 6, wherein the voltage comparator further comprises: A seventh P-type transistor, whose input terminal is connected to the second voltage and whose control terminal is connected to the control terminals of the fifth P-type transistor and the sixth P-type transistor; a fifth N-type transistor, whose input terminal is grounded and whose output terminal is connected to the control terminal and also connected to the output terminal of the sixth P-type transistor; and a sixth N-type transistor, whose input terminal is grounded, whose control terminal is connected to the control terminal of the fifth N-type transistor, and whose output terminal is connected to the output terminal of the seventh P-type transistor.

8. The voltage selection circuit as claimed in claim 7, wherein the third N-type transistor and the fourth N-type transistor, the fifth N-type transistor and the sixth N-type transistor, and the fifth P-type transistor and the sixth P-type transistor respectively constitute a current mirror circuit.

9. The voltage selection circuit as described in claim 7, wherein when the first voltage is close to the second voltage, the voltage output node outputs the first voltage as the maximum voltage.

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