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Automatic Low Loss Power Transfer Technique for Regulators

IP.com Disclosure Number: IPCOM000109543D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 90K

Publishing Venue

IBM

Related People

Keidl, SD: AUTHOR

Abstract

A significant amount of power is lost in switching regulator power supplies due to conversion of the source voltage to a level usable by the switching regulator control circuits. This power loss can cause significant reduction in regulator overall efficiency. The circuit technique described here greatly reduces this loss by implementing an automatic, low loss load transfer from the source voltage to the output voltage, the load being defined as all the circuitry in the regulator required for its operation that cannot run directly off the source voltage, Vs.

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Automatic Low Loss Power Transfer Technique for Regulators

       A significant amount of power is lost in switching
regulator power supplies due to conversion of the source voltage to a
level usable by the switching regulator control circuits.  This power
loss can cause significant reduction in regulator overall efficiency.
The circuit technique described here greatly reduces this loss by
implementing an automatic, low loss load transfer from the source
voltage to the output voltage, the load being defined as all the
circuitry in the regulator required for its operation that cannot run
directly off the source voltage, Vs.

      The circuit shown in Fig. 1 illustrates the technique for a 5-
volt output and 24-volt input regulator.  Initially, when power is
applied to the Vs input of the regulator, transistor Q2 turns on.
This action causes +base drive to be applied to Q5, turning it on and
raising the voltage at Q5 emitter until it reaches the reference
zener voltage of D4.  Q2 and Q5 form a negative feedback loop which
stabilizes at Vcc = VD4+Vbe(Q5).  This is about 4.9 volts for the
example circuit shown.  This voltage, Vcc, then powers the control
circuits until the regulator output, Vout, reaches approximately VD4
or 4.2 volts.  At this point, Q3 of the differential pair begins to
conduct.  As the output, Vout, continues to go positive, Q3
conduction turns on Q1 and turns off Q4.  Turning off Q4 forces Q5 on
hard, causing Q2 to turn off.  The controll...