Browse Prior Art Database

Method of Pre-Charging Logic Card (Decoupling) Capacitors

IP.com Disclosure Number: IPCOM000035415D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 80K

Publishing Venue

IBM

Related People

Myers, WV: AUTHOR [+2]

Abstract

It is desirable to be able to replace a faulty logic card without otherwise disturbing system operation. Logic cards contain voltage-to-ground decoupling capacitors which draw large current surges when voltages are first applied. These surges can reach hundreds of amperes for a duration of a few microseconds. Such surge currents will cause a dip in bus voltages which can lead to logic errors. These currents can also cause pitting of connector contacts. The currents also cause radiated electrical noise which may affect the operation of adjacent logic.

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Method of Pre-Charging Logic Card (Decoupling) Capacitors

It is desirable to be able to replace a faulty logic card without otherwise disturbing system operation. Logic cards contain voltage-to-ground decoupling capacitors which draw large current surges when voltages are first applied. These surges can reach hundreds of amperes for a duration of a few microseconds. Such surge currents will cause a dip in bus voltages which can lead to logic errors. These currents can also cause pitting of connector contacts. The currents also cause radiated electrical noise which may affect the operation of adjacent logic.

Referring to Fig. 1, by slowly applying the voltage, the surge current can be kept within acceptable limits. Every card connector has a long pin 1 for each required voltage and for ground. As the card is

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being inserted, the long pins make contact first which causes a current to flow through a sense resistor Rs. The voltage pulse thus generated across Rs is sensed by the operational amplifier 2 which triggers a single-shot ramp generator
4. The ramp is applied to the gates of all the hexfet transistors 6, but only the one connected to the particular logic card being plugged is active. (All the others are either open or shorted.) The voltage to the card may be ramped up on less than one millisecond so that capacitors 8 are nearly fully charged by the time the short pin 10 makes contact. The making of the short pin shorts out the hexfet 6 and appl...