| 摘要 |
A circuit board having a load is inserted into a chassis of a digital system while the system remains in operation. During insertion, a ground potential is provided to the circuit board. Next, one or more voltage potentials are provided, however, no electrical path is provided from the voltage potentials, through the load, to ground. An enhancement voltage is provided to the circuit board, allowing the load to charge. Finally, a backplane is connected to the circuit board after the load has charged. The circuit board includes a soft start circuit that allows the load to charge gracefully after the enhancement voltage is provided. In one embodiment, the soft start circuit includes an RC circuit connected to a switch which gradually turns on as the RC circuit charges, thereby providing an electrical path from the circuit board load to ground through the switch. The switch may be a MOSFET. Once the circuit board load is charged, connecting the backplane bypasses the MOSFET, thereby eliminating nearly all quiescent current flow through, and associated power dissipation in, the MOSFET. The circuit board is extracted from the chassis of the digital system by first disconnecting the backplane. When this occurs, the MOSFET is no longer bypassed by the backplane connection and quiescent current again flows through the MOSFET. Next, the enhancement voltage is removed, allowing the MOSFET to gradually turn off as the RC circuit discharges, thereby removing the electrical path from the load to ground. The voltage and ground potential are then removed.
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