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Load Setting 240-Volt Amp Protector

IP.com Disclosure Number: IPCOM000121868D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Egan, PK: AUTHOR

Abstract

Safety standards for computers and other electronic equipment require that the accessible power at any exposed electrical contact be limited to 240 volt-amps (VA).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Load Setting 240-Volt Amp Protector

      Safety standards for computers and other electronic
equipment require that the accessible power at any exposed electrical
contact be limited to 240 volt-amps (VA).

      Safety protection can be accomplished by packaging to prevent
access, using interlock switches to remove the power or splitting the
power into branch circuits each electronically limited to 240 VA.

      Described is a protection circuit that will support a load of
greater than 240 VA while still limiting the accessible power to safe
limits, thus avoiding the cost and complexity of other methods.

      The schematic diagram of the load setting 240 VA protection
circuit is shown in the figure.  This circuit contains a conventional
overcurrent detector consisting of op-amp M2, comparator M3, and
resistors R2 through R6.  As the current IOUT increases, the voltage
at the inverting input to M3 increases accordingly.  When this
voltage exceeds the reference voltage at the non-inverting input of
M3, the "-OC" output will fall to a low level, which will be used to
remove Vin power.  In a conventional overcurrent circuit the voltage
at the non-inverting input of M3 would be a fixed reference voltage.
What makes this circuit different is the addition of op-amp M1,
resistor R1 and the "OC SET" line.  The "OC SET" line runs through
the system connecting to every load that uses the output voltage
Vout.  Each of these loads contains a resistor (Rs1..Rsn) that has a
value inversely proportional to the load's minimum load current.
           Rsn = K / In(min)     WHERE K IS A CONSTANT

      As loads are added to the system, RS resis...