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Plural electric power supplies are connected in parallel to an output bus. The plural supplies include a primary power supply and a redundant switching power supply. The primary power supply is configured to provide output current to a load when the primary power supply is operating normally. The re

Plural electric power supplies are connected in parallel to an output bus. The plural supplies include a primary power supply and a redundant switching power supply. The primary power supply is configured to provide output current to a load when the primary power supply is operating normally. The redundant supply is configured to remain online while not providing output current to the load when the primary power supply is operating normally, but to begin providing output current to the load when the primary power supply is not operating normally.

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1. A system, comprising: a plurality of electric power supplies connected in parallel to an output bus, the plurality including at least one primary power supply and at least one redundant switching power supply;wherein the primary power supply is configured to provide output current to a load when

1. A system, comprising: a plurality of electric power supplies connected in parallel to an output bus, the plurality including at least one primary power supply and at least one redundant switching power supply;wherein the primary power supply is configured to provide output current to a load when the primary power supply is operating normally; andwherein the redundant switching power supply is configured to remain online while not providing output current to the load when the primary power supply is operating normally, but to begin providing output current to the load when the primary power supply is not operating normally, wherein the output current is direct current (DC). 2. The system of claim 1, wherein: the primary supply is configured to provide current at a first maximum voltage and the redundant switching power supply is configured to provide current at a second maximum voltage lower than the first maximum voltage. 3. The system of claim 2, wherein: the first and second maximum voltages are both within a range of input voltages tolerated by the load. 4. The system of claim 3, wherein: the first maximum voltage is equal to a desired input voltage for the load; and the second maximum voltage is sufficiently lower than the first maximum voltage that control circuitry in the redundant supply does not operate an output converter in the redundant switching power supply while the primary supply is providing current to the load at the desired input voltage for the load. 5. The system of claim 4, wherein: the range of input voltages tolerated by the load has a minimum tolerated voltage; andthe second maximum voltage is sufficiently higher than the minimum tolerated voltage that, should the primary supply fail, the control circuitry in the redundant switching power supply will begin to operate the output converter in the redundant switching power supply before the voltage on the output bus falls below the minimum tolerated voltage. 6. The system of claim 2, wherein: a maximum output voltage for at least two supplies in the plurality of supplies is programmable such that a control system, by programmatically setting the maximum output voltages of the at least two supplies, can determine which of the at least two supplies will be the redundant supply. 7. The system of claim 1, further comprising: a diode connecting a storage element in the redundant switching power supply to the output bus, the diode oriented such that it becomes forward biased when a voltage at the storage element exceeds a voltage on the output bus by a threshold amount; anda switching element connected in parallel with the diode. 8. The system of claim 7, wherein: the primary supply is configured to provide current to the load at a desired input voltage for the load; andthe redundant switching power supply is configured such that the voltage at the storage element will not exceed the desired input voltage for the load by the threshold amount, so that the diode will not become forward biased while the primary supply is providing current to the load at the desired input voltage. 9. The system of claim 8, further comprising: sensing circuitry configured to indicate whether the redundant switching power supply is supplying any current to the output bus; andcontrol circuitry configured to turn on the switching element to bypass the diode when the sensing circuitry indicates that the redundant switching power supply is supplying current to the output bus. 10. The system of claim 1, further comprising: soft start circuitry and an output converter in the redundant switching power supply; andcontrol circuitry configured to change behavior of the soft start circuitry when the output converter is to be enabled and the output bus has been charged to at least a first threshold. 11. The system of claim 10, further comprising: sensing circuitry configured to indicate whether the voltage on the output bus has dropped below a second threshold; andwherein the control circuitry is configured to enable the output converter when the voltage on the output bus has dropped below the second threshold. 12. The system of claim 11, wherein: the second threshold is equal to the first threshold. 13. The system of claim 10, wherein: the control circuitry changes the behavior of the soft start circuitry by disabling soft start. 14. The system of claim 10, wherein: the control circuitry changes the behavior of the soft start circuitry by reducing the duration of a soft start time interval. 15. A method of operating a plurality of electric power supplies connected to an output bus, the plurality including at least one primary power supply and at least one redundant switching power supply, the method comprising: operating the primary supply such that it provides output current to a load connected to the output bus, and simultaneously maintaining the redundant switching power supply in an online state wherein it does not provide output current to the load;detecting a fault condition; andresponsive to detecting the fault condition, causing the redundant switching power supply to provide output current to the load, wherein the output current is direct current (DC). 16. The method of claim 15, further comprising: setting an output voltage of the primary supply to a first maximum voltage; andsetting an output voltage of the redundant switching power supply to a second maximum voltage lower than the first maximum voltage. 17. The method of claim 15, wherein: detecting the fault condition comprises detecting that a diode at an output of the redundant switching power supply has become forward biased; andcausing the redundant switching power supply to provide output current to the load comprises turning on a switching element to bypass the diode. 18. The method of claim 15, wherein: causing the redundant switching power supply to provide output current to the load comprises enabling an output converter of the redundant supply while changing the behavior of soft start circuitry in the redundant supply. 19. The method of claim 18, wherein: changing the behavior of the soft start circuitry comprises disabling the soft start circuitry. 20. The method of claim 18, wherein: changing the behavior of the soft start circuitry comprises reducing the duration of a soft start time interval.