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

Circuit Configuration for Power Limiting in Personal Computer Monitors

IP.com Disclosure Number: IPCOM000117395D
Original Publication Date: 1996-Feb-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Duddridge, G: AUTHOR

Abstract

It is desirable to limit the power throughput in a Personal Computer (PC) monitor in order to prevent overloading of components under fault conditions and to allow cost efficient design.

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

Circuit Configuration for Power Limiting in Personal Computer Monitors

      It is desirable to limit the power throughput in a Personal
Computer (PC) monitor in order to prevent overloading of components
under fault conditions and to allow cost efficient design.

      By way of solution to the above problem, power limiting is
achieved by combining three currents, each of which represents a
single component required for effective throughput power limiting.
The three component parts are:
  1.  A frequency related component.
  2.  An AC input voltage related component.
  3.  A control chip offset related component.

      By utilizing a current sourcing and sinking circuit
configuration, the power throughput of the monitor PSU is
substantially constant at any of the operating frequencies,
independent of supply voltage and circuit component variations.

      In this circuit, as shown in the Figure, Z101 supplies a
constant voltage supply, Vref, under normal operating conditions.
This supply is used to create a constant current through Q102, R107,
RV101, R106, Q103 and R118.  Q101 and R105 act as a current mirror
capable of sinking an identical current to that flowing through Q103
and R118.  Q105 and R117 form a variable current source, controlled
by RV100 and capable of providing sufficient current to meet the
current requirements of Q101 and R105.

      Any additional current supplied by Q105 and R117 is available
to drive the resistive load, R131 via CR105.  This offset current
compensates for the variation of up to 200mV in the threshold level
of the current sense comparato...