Browse Prior Art Database

Sensing of Network Supplied Power Via Pulsed Coupling

IP.com Disclosure Number: IPCOM000122222D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 36K

Publishing Venue

IBM

Related People

Bentley, AM: AUTHOR [+4]

Abstract

A DC voltage is typically present on ISDN telephone lines. It is required that the device to be attached to ISDN networks be able to detect the absence of this DC voltage. The design described herein is a method of sensing the presence of this DC voltage while meeting requirements for high voltage isolation and low power consumption.

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Sensing of Network Supplied Power Via Pulsed Coupling

      A DC voltage is typically present on ISDN telephone
lines. It is required that the device to be attached to ISDN networks
be able to detect the absence of this DC voltage. The design
described herein is a method of sensing the presence of this DC
voltage while meeting requirements for high voltage isolation and low
power consumption.

      Electrical isolation of the ISDN phone line from the attached
device is a requirement of attachment.  (See the figure.)  Typically,
power consumption restrictions do not allow enough power for
continuous operation of electrical isolation devices such as
Optoisolaters.  The solution is to use a pulsing electrical circuit
to provide an indication that the power source is present instead of
a continuously 'on' circuit.
     -  A resistor is used to limit the power drawn from the ISDN
phone line.
     -  The power is stored in a capacitor to accumulate enough power
to 'fire' an electrical isolation device such as an optoisolator.
     -  Current shut-off circuitry is employed to prevent a slow
drain of power from the capacitor.  This allows enough power to be
accumulated to 'fire' a device, such as an optoisolator, and thus
producing a pulse to indicate that DC power is active.
     -  An electrical isolation device, such as an optoisolator, must
be used to meet voltage isolation safety requirements.
     -  A pulse detection circuit must be on t...