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Over Voltage/Under Voltage Detect Circuit for Redundant Negative Output TL431 MAG-AMP Circuits

IP.com Disclosure Number: IPCOM000115179D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Allen, JM: AUTHOR

Abstract

The disclosed circuit is a pre-output overvoltage/undervoltage (OV/UV) detect circuit for diode-isolated redundant (parallelable) tight-voltage-toleranced negative-output TL431 (adjustable zener diode) controlled mag-amp circuits. It utilizes only an opamp and feedback resistors in addition to normal OV/UV circuitry.

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Over Voltage/Under Voltage Detect Circuit for Redundant Negative
Output TL431 MAG-AMP Circuits

      The disclosed circuit is a pre-output overvoltage/undervoltage
(OV/UV) detect circuit for diode-isolated redundant (parallelable)
tight-voltage-toleranced negative-output TL431 (adjustable zener
diode) controlled mag-amp circuits.  It utilizes only an opamp and
feedback resistors in addition to normal OV/UV circuitry.

      In the Figures, the higher part is the mag-amp converter
(engine).  D1 is the isolation diode.  RSENSE is the overcurrent (OC)
sense resistor, placed on ground for tight voltage tolerance.  Vb is
the negative output of the engine.  R1, R2 and R3 are the voltage
sense resistors the TL431 uses to regulate the output voltage.  Va is
a voltage that is fed to the OV/UV circuitry.

      The lower section is the OV/UV sense circuitry.  Va and Vb are
the same nodes as Va and Vb in the higher section.  Vc is just a node
used for operation description.  The resistors R4-R9 are sized for
the OV and UV design points.  R7, R8 and R9 make up a normal resistor
tree for OV/UV detection.

      The circuit functions as follows.  R4, R6, and the Op-amp form
a basic inverter so that Vc = -Vb.  Va is a low positive voltage near
ground.  Without R5, and assuming Va = 0V, the circuit would be
somewhat of a normal OV/UV circuit.  However, since Va varies in
voltage, R5 is used to feed it back and move Vc opposite Va; thus the
UV and OV set points...