Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

"Hot-Plug" Protection Circuit

IP.com Disclosure Number: IPCOM000113584D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 218K

Publishing Venue

IBM

Related People

Patterson, BE: AUTHOR

Abstract

Disclosed is a circuit for preventing high current surges and low voltage dips at a low voltage source, which may be, for example, 5 volts or less, or at relatively high voltages, such as 12 volts. These current and voltage transients, which may occur as a device is "hot-plugged," being connected or disconnected without removing electrical power, could otherwise cause errors in other parts of a system connected to the voltage source. This protection circuit also provides for current through the external circuit to be turned on slowly as voltage source is turned on or as the external circuit is connected. Protection against a short circuit is provided both during connection of the external circuit and during subsequent operation of the external circuit.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 27% of the total text.

"Hot-Plug" Protection Circuit

      Disclosed is a circuit for preventing high current surges and
low voltage dips at a low voltage source, which may be, for example,
5 volts or less, or at relatively high voltages, such as 12 volts.
These current and voltage transients, which may occur as a device is
"hot-plugged," being connected or disconnected without removing
electrical power, could otherwise cause errors in other parts of a
system connected to the voltage source.  This protection circuit also
provides for current through the external circuit to be turned on
slowly as voltage source is turned on or as the external circuit is
connected.  Protection against a short circuit is provided both
during connection of the external circuit and during subsequent
operation of the external circuit.

      The Figure is a schematic diagram of the hot-plug protection
circuit, in which a power FET 10 (Field Effect Transistor) is placed
between an input terminal 12, at which the source voltage VIN is
applied, and an output terminal 14.  A power source 15 is connected
between a return terminal 16  and input terminal 12.  An external
load 17 is connected between output terminal 14 and return terminal
18.  The FET 10 is controlled in stages by associated components to
turn on slowly, to be fully on with a minimum voltage drop, and to
turn off.  A negative voltage generated elsewhere in the source,
indicated as -VEE, is applied to terminals 19 and 20.

      The circuit functions in four modes of operation.  In Mode 1,
operation of the circuit is started with an external circuit
attached.  In Mode 2, the system is started without the external
circuit attached, and the external circuit is "hot-plugged" into
running circuitry.  The electrical power applied to the external
circuit in an orderly manner to continue operation with the external
circuit attached.  In Mode 3, a short circuit is detected during
normal operation, FET 10 is turned off, and recovery occurs only when
the short circuit and load are removed.  Finally, in Mode 4, the
system is started with an external circuit, having a short circuit,
attached.  Again, FET 10 is turned off, and recovery occurs only when
the short circuit and load are removed.

      Thus, the operation in Mode 1 (start-up and operate with the
external circuit attached) is begun as the voltage source is applied
between input terminal 12 and return terminal 16.  As VIN is turned
on, FET 10 is off, since the source-to-gate voltage of this FET is
initially zero volts.  Thus, as the source voltage initially
increases, current flows through a first parallel path provided by
capacitor 21, and a second parallel path provided by the
emitter-to-base path through bipolar transistor 22, by resistor 24,
and by capacitor 26, instead of through FET 10.  This current turns
transistor 22 on, keeping the gate-to-source voltage of FET 10 very
low, so that the FET is held in a turned-off condition.

      Subs...