Circuit board insertion circuitry for high reliability backplanes

摘要

Circuit board insertion circuitry is used in conjunction with a staggered electrical connector. The insertion circuitry includes an isolated circuit which receives a high system voltage upon first stage contact between the card and a high voltage bus, and uses that high system voltage to tristate the output of a transceiver on the circuit board prior to second stage contact being made between the transceiver and the backplane data bus. Override circuitry for overriding the tristating effects of the isolating circuit are provided such that when the bias circuit which controls the transceiver output is properly powered, the bias circuit will control the transceiver output, and not the isolated circuit. Additional circuitry which isolates the circuit board so that a power fault on the board will not impact other boards on the backplane is also provided. The additional circuitry preferably includes a relative large resistor and a Schottky diode which are provided in parallel between a 5 V bus and the protection diodes of the transceiver.