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Application Notes

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  High Efficiency Linear Regulators &mdash AN32
  PDF, 818 Kb, File published: Mar 1, 1989
  Presents circuit techniques permitting high efficiency to be obtained with linear regulation. Particular attention is given to the problem of maintaining high efficiency with widely varying inputs, outputs and loading. Appendix sections review component characteristics and measurement methods.
  Extract from the document

  Application Note 32
  March 1989
  High Efficiency Linear Regulators
  Jim Williams
  Introduction
  Linear voltage regulators continue to enjoy widespread use
  despite the increasing popularity of switching approaches.
  Linear regulators are easily implemented, and have much
  better noise and drift characteristics than switchers. Additionally, they do not radiate RF, function with standard
  magnetics, are easily frequency compensated, and have
  fast response. Their largest disadvantage is inefficiency.
  Excess energy is dissipated as heat. This elegantly simplistic regulation mechanism pays dearly in terms of lost
  power. Because of this, linear regulators are associated
  with excessive dissipation, inefficiency, high operating
  temperatures and large heat sinks. While linears cannot
  compete with switchers in these areas they can achieve
  significantly better results than generally supposed. New
  components and some design techniques permit retention of linear regulator’s advantages while improving
  efficiency.
  One way towards improved efficiency is to minimize the
  input-to-output voltage across the regulator. The smaller
  this term is, the lower the power loss. The minimum input/
  output voltage required to support regulation is referred …

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  Voltage Reference Circuit Collection &mdash AN42
  PDF, 1.7 Mb, File published: Jun 1, 1991
  A wide variety of voltage reference circuits are detailed in this extensive guidebook of circuits. The detailed schematics cover simple and precision approaches at a variety of power levels. Included are 2 and 3 terminal devices in series and shunt modes for positive and negative polarities. Appended sections cover resistor and capacitor selection and trimming techniques.
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  5V to 3.3V Converters for Microprocessor Systems &mdash AN58
  PDF, 310 Kb, File published: Sep 1, 1993
  Many popular microprocessors operate from 3.3V supplies, yet they are used in systems where the predominate source of power is 5V. AN58 presents a collection of both linear and switching regulator solutions for conversion of 5V to 3.3V at currents ranging from 100mA to 20A. Applications information and a comparison of various bypass capacitor types is included. Most of the designs can be easily modified for other intermediate voltages such as 3.45V, 3.7V, and 4.1V.
  Extract from the document

  Application Note 58
  September 1993
  5V to 3.3V Converters for Microprocessor Systems
  Robert Dobkin, Mitchell Lee, Dennis O'Neill and Milt Wilcox
  Introduction Linear Regulators The new generation of high performance microprocessors are built on dense, low breakdown voltage processes
  in order to accommodate increased transistor counts.
  These new processors require high current power at 3.3V,
  developed from the 5V input used to power the rest of the
  system. Special techniques are required to ensure proper
  operation of the microprocessor and good heat dissipation within the computer system. Table 1 shows the range of components available for linear
  regulation of 3.3V with a 5V input. With only 1.7V of
  headroom, low dropout is essential. Low dropout regulators are available delivering currents from 125mA to 7.5A,
  allowing almost any microprocessor to be powered with a
  local 3.3V generation circuit. The first four devices (LT1020,
  LT1120, LT1121 and LT1129) are PNP micropower low
  dropout regulators. Since PNP transistors are much larger
  than monolithic NPNs, higher current regulators use an
  NPN pass device. The LT1117, LT1086, LT1083 through
  LT1085, and LT1087 all use NPN pass devices. The NPN
  structure requires about 1.2V headroom compared to the
  400mV to 500mV dropout typical of PNP regulators, and
  ground current of 5mA or 10mA, independent of output
  current. Because of this constant quiescent current, the …

Design Notes

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  2 AA Cells Replace 9V Battery, Extend Operating Life &mdash DN63
  PDF, 76 Kb, File published: Oct 1, 1992
  Extract from the document

  advertisement 2 AA Cells Replace 9V Battery, Extend Operating Life
  Design Note 63
  Steve Pietkiewicz
  Operating life is an important feature in many portable
  battery-operated systems. In many cases the power
  source is the ubiquitous 9V “transistor” battery. 5V
  generation is accomplished with a linear regulator. Significant gains in battery life can be obtained by replacing
  the 9V/linear regulator combination with 2 AA cells and
  a step-up switching regulator. Two (alkaline) AA cells
  occupy 1.3 cubic inches, the same as a 9V battery, but
  contains 6WH of energy, compared to just 4WH in an
  alkaline 9V battery. Two AA cells also cost less than a 9V
  battery.1 The additional energy in the AA cells provides
  longer operating life when compared to a 9V battery
  based solution.
  An evaluation of the three approaches with a 30mA load
  illustrates the differences in battery life. An HP7100B
  strip chart recorder provides a nonvolatile record of
  circuit performance. The linear regulator circuit shown
  in Figure 1 uses an LTВ®1120 micropower low dropout
  regulator IC. A minimum of external components are required. No inductors or diodes are needed; however, the
  linear step-down process is inherently inefficient. The
  step-down switcher shown in Figure 2 uses an LT1173 …

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Manufacturer's Classification

• Power Management > LDO Linear Regulators > Positive Linear Regulators (LDO)