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Circuit Allowing Installation and Removal of a Device under Power

IP.com Disclosure Number: IPCOM000113630D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Brandl, TA: AUTHOR

Abstract

Disclosed is a circuit for allowing the installation or removal of a pluggable device, such as a Direct Access Storage Device (DASD), from a computing system without turning off system power. A MOSFET field effect transistor in each of the power supply lines is controlled by an integrated circuit so that the voltage on the line to the device rises and falls in a controlled manner, preventing damage to elements, such as electrolytic capacitors, within the device, and reducing transient conditions on the system power lines supplying the device. Each MOSFET transistor provides a means of control over the load power-up profile, particularly controlling the undesired effects of contact bounce and power surge.

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Circuit Allowing Installation and Removal of a Device under Power

      Disclosed is a circuit for allowing the installation or removal
of a pluggable device, such as a Direct Access Storage Device (DASD),
from a computing system without turning off system power.  A MOSFET
field effect transistor in each of the power supply lines is
controlled by an integrated circuit so that the voltage on the line
to the device rises and falls in a controlled manner, preventing
damage to elements, such as electrolytic capacitors, within the
device, and reducing transient conditions on the system power lines
supplying the device.  Each MOSFET transistor provides a means of
control over the load power-up profile, particularly controlling the
undesired effects of contact bounce and power surge.  Since the
device can now be removed and replaced while the system is
operational, the overall reliability, availability, and
serviceability of the system operating in, for example, a server
mode, is significantly improved.

      As shown in the Figure, a device 10, having circuits 12, is
removably attached to a system 14, with electrical power and ground
connections from the system being made at an interface 16.  The
fundamental component required to allow the connection and
disconnection of device 10 without turning off the power of system 14
is a MOSFET switch.  Very little energy is consumed in turning on a
MOSFET field effect transistor, because it is a voltage-driven
device, unlike a current-driven bipolar transistor or relay switch.
While a disadvantage of the MOSFET transistor is the voltage drop
resulting from channel resistance, N-channel MOSFET transistors, in
the TO-220 package, can be found to pass up to 5 amps with acceptable
voltage drops.  While a P-channel MOSFET transistor is relatively
easy to turn on because it requires a voltage level below that of the
supply, a P-channel transistor exhibits an inherently higher channel
resistance, resulting in an intolerable voltage drop from power
source to load.  On the other hand, an N-channel MOSFET transistor
has a much lower channel resistance, one eighth to one quarter that
of a similar-size P-channel transistor, but the N-channel transistor
must be turned on using a voltage higher than...