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Feedback Circuit for Display Power Supplies

IP.com Disclosure Number: IPCOM000104914D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Eagle, DJ: AUTHOR [+2]

Abstract

Disclosed is a simple, cost-effective way to provide synchronization and voltage feedback in a display by bridging the primary/secondary gap with a single opto-isolator. Periodic superimposition of the sync information on the voltage feedback signal is the key feature with component cost savings over existing designs.

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Feedback Circuit for Display Power Supplies

      Disclosed is a simple, cost-effective way to provide
synchronization and voltage feedback in a display by bridging the
primary/secondary gap with a single opto-isolator.  Periodic
superimposition of the sync information on the voltage feedback
signal is the key feature with component cost savings over existing
designs.

      The power supply in a display usually utilizes two control
signals.  First is a voltage feedback signal, used to regulate output
voltage.  It can be a simple rectified primary tap on the SMPS
transformer, but a better solution is to take a signal directly from
the high voltage output rail and feed it back across the
primary/secondary gap, providing better regulation.  Another signal
usually required is sync to synchronize power supply to line scan;
otherwise, additional magnetic screening of the power supply is
necessary.  Again, the signal needs to be fed back across the
primary/secondary gap.  A cost-effective way of feeding back the
signals across the gap is described below.

      The new circuit is shown in the figure.  The B+ rail is the
regulated rail.  Voltage on the base of Q2 is determined by the value
of B+ and the ratio R9/R10.  Current flow through the Z3
opto-isolator LED is fixed by Q2 emitter voltage, the value of the D4
zener diode and resistor R12.  T3 is a tap on the FBT transformer;
using the heater tap is permissible if the polarity is correct,
positive-going d...