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

Load Tracking Switch Mode Power Supply Regulator

IP.com Disclosure Number: IPCOM000102675D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 6 page(s) / 183K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR [+2]

Abstract

A power supply regulator circuit is described which provides load tracking switch mode capability so as to enable a power supply to operate efficiently under widely varying loads.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 42% of the total text.

Load Tracking Switch Mode Power Supply Regulator

       A power supply regulator circuit is described which
provides load tracking switch mode capability so as to enable a power
supply to operate efficiently under widely varying loads.

      In prior art, switch mode power regulation required that there
always be a minimum load on a power supply so as to avoid loss of
current flow in the inductor.  This resulted in poor operational
efficiency due to large direct current losses in the system.
Generally, the common solution to solve this problem was to provide a
minimum load by utilizing a resistor positioned across the output of
the power supply.  This resulted in wasted power.  Where batteries
were used to power the application, the life of the battery was
shortened.

      The concept described herein is an improvement to the prior-art
approach in that it provides a load tracking switching mode
regulation capability to enable a power supply to operate efficiently
when loads vary widely.  The circuit also supplies a regulated
voltage which is greater than the input voltage.

      In prior art, a basic step-up switching voltage regulator was
used.  Fig. 1 shows a block diagram of the step-up switching
approach. Transistor 10 switches at a fixed frequency determined by
oscillator 11.  The duty cycle or the pulse width is determined by
comparator 12.  When transistor 10 is ON, current flows from Vin
through fixed inductor 13 creating a magnetic field in inductor 13.
Diode 14 is reverse biased during this time.  When transistor 10
turns OFF, the magnetic field in inductor 13 collapses, the voltage
at node V1 rises and diode 14 becomes forward biased.  This enables
the current from inductor 13 to be absorbed into capacitor 15,
thereby charging capacitor 15.

      Fig. 2 shows a block diagram of the concepts of a load tracking
switch mode voltage regulator.  Two improvements are incorporated:
First, fixed inductor 13 is replaced by swinging inductor 16.  A
swinging inductor, or choke, is an inductor with a core material
whose permeability changes significantly with its flux density.  As
the flux increases, due to larger inductor current, the value of the
inductance decreases.
                      2.5 Vin2 (Vo-Vin)
         Inductance = -----------------
   (1)
                      FREQ x Io x Vo2

      Referring to equation (1), it can be seen that as the value of
Io decreases, the calculated inductance value increases.  By using
swinging inductor 16, the circuit can provide an inductance which is
five times greater at I=0 than at I=Imax.  Fig. 3 shows a current vs.
inductor plot for a typical swinging inductor.  The varying
inductance helps preserve the design rule of maintaining
approximately 40% of the Io current circulating in the inductor.

      The concept's second improvement is that fixed frequency
oscillator 11 (Fig. 1) is replaced with...