| 摘要 |
A switching circuitry for coupling the power output of one of a plurality of power supplies to a keyboard. In this disclosure, a switching transistor of the circuit is coupled to switch power from a power supply output to a common point to which a plurality of like circuits and a keyboard are coupled. A differential amplifier having one input coupled to the common point and another input coupled to the power output of the respective power supply compares voltage on the common point to the voltage of the power supply. If the power supply voltage is higher than the voltage on the common point, the amplifier provides an enabling signal to the transistor, coupling power from the power supply to the common point. Conversely, if the voltage on the common point is higher than the voltage of the power supply output, the amplifier provides a disabling signal to the transistor, decouping the power supply output from the common point. Diodes shunt the switching transistors in order to provide power to the differential amplifiers.
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