| 摘要 |
A voltage regulator for producing an output voltage that selectively tracks a logic voltage or a reference voltage and method of operating the voltage regulator. The voltage regulator has a diode OR with a logic and reference transistors. The logic voltage is scaled to be close in value to the reference voltage, if the two are not close in value. When the scaled logic voltage is larger than the reference voltage the logic transistor is on, turning off the reference transistor and passing the logic voltage to the output of the diode OR. When the scaled logic voltage is smaller than the reference voltage the logic transistor is off and the reference transistor is on, passing the reference voltage to the output of the diode OR. The voltage at the output of the diode OR is then compared in a comparator with the voltage at the output of the voltage regulator, which is scaled by the same factor as the logic voltage. The comparator increases the output voltage if it is smaller than the voltage at the output of the diode OR, and decreases the output voltage if it is larger than the voltage at the output of the diode OR. This permits the circuitry attached to the voltage regulator to operate when the logic voltage is not present, and to operate at the exact same voltage as the logic voltage when the logic voltage is present.
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