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Anwendungshinweise

• Herunterladen
  Illumination Circuitry for Liquid Crystal Displays &mdash AN49
  PDF, 5.3 Mb, Datei veröffentlicht: Aug 23, 1992
  Current generation portable computers and instruments utilize backlit liquid crystal displays. The back light requires a highly efficient, high voltage AC source as well as other supply circuitry. AN49 details these circuits and also includes sections on efficiency measurements and instrumentation considerations. A separate section discusses physical and layout considerations for the display.
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  Power Conditioning for Notebook and Palmtop Systems &mdash AN51
  PDF, 260 Kb, Datei veröffentlicht: Aug 3, 1992
  Notebook and palmtop systems need a number of voltages developed from a battery. Competitive solutions require small size, high efficiency and light weight. This publication includes circuits for high efficiency 5V and 3.3V switching and linear regulators, back light display drivers and battery chargers. All the circuits are specifically tailored for the requirements outlined above.
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  Application Note 51
  August 1992
  Power Conditioning for Notebook and Palmtop Systems
  Robert Dobkin
  Carl Nelson
  Dennis O’Neill
  Steve Pietkiewicz
  Tim Skovmand
  Milt Wilcox
  INTRODUCTION Battery systems include NiCad, nickel-hydride, lead acid,
  and rechargeable lithium, as well as throw-away alkaline
  batteries. The ability to power condition a wide range
  of batteries makes the ultimate product much more
  attractive because power sources can be interchanged,
  increasing overall system versatility. a very high efficiency (Figure 1) 5V or 3.3V step-down
  (buck) switching regulator. These regulators feature a
  low-loss saturating NPN switch that is normally configured with the negative terminal (emitter) at ground. The
  LT1432 allows the switch to be floated as required in a
  step-down converter, yet still provides full switch saturation for highest efficiency.
  Burst ModeTM is a trademark of Linear Technology Coporation. 100
  NORMAL MODE
  (USE AMPS SCALE)
  90 EFFICIENCY (%) Notebook and palmtop systems need a multiplicity of …

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  Techniques for 92% Efficient LCD Illumination &mdash AN55
  PDF, 688 Kb, Datei veröffentlicht: Aug 1, 1993
  This publication details several LCD backlight circuits which feature 92% efficiency. Other benefits include low voltage operation, synchronizing capability, higher output power for color displays, and extended dimming range. Extensive coverage of practical issues includes layout problems, multi-lamp displays, safety and reliability concerns and efficiency and photometric measurements. Also included is a review of circuits which did not work along with appropriate commentary.
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  Application Note 55
  August 1993
  Techniques for 92% Efficient LCD Illumination
  Waste Not, Want Not .
  Jim Williams
  INTRODUCTION
  In August of 1992 LTC published Application Note 49,
  “Illumination Circuitry for Liquid Crystal Displays.” One
  notable aspect of this event is that it generated more
  response than all previous LTC application notes combined. This level of interest, along with significant performance advances since AN-49’s appearance, justifies
  further discussion of LCD backlighting circuitry.
  This publication includes pertinent information from the
  previous effort in addition to updated sections and a large
  body of new material. The partial repetition is a small
  penalty compared to the benefits of text flow, completeness and time efficient communication. The most noteworthy performance advance is achievement of 92%
  efficiency for the backlight power supply. Additional new
  benefits include low voltage operation, synchronizing capability, higher output power for color displays, and extended dimming range.
  A practical 92% efficient LCD backlight design is a classic
  study of compromise in a transduced electronic system.
  Every aspect of the design is interrelated, and the physical
  embodiment is an integral part of the electrical circuit. The
  choice and location of the lamp, wires, display housing
  and other items has a major effect on electrical characteristics. The greatest care in every detail is required to …

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  Practical Circuitry for Measurement and Control Problems &mdash AN61
  PDF, 1.1 Mb, Datei veröffentlicht: Aug 1, 1994
  This collection of circuits was worked out between June 1991 and July of 1994. Most were designed at customer request or are derivatives of such efforts. Types of circuits include power converters, transducer signal conditioners, amplifiers and signal generators. Specific circuits include low noise amplifiers, high power single cell DC/DC converters, portable high accuracy barometers, a 10mHz 1% accuracy RMS/DC converter, and random noise generators. Appended sections cover noise theory and present a historical perspective of wideband amplifiers.
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  Application Note 61
  August 1994
  Practical Circuitry for Measurement and Control Problems
  Circuits Designed for a Cruel and Unyielding World
  Jim Williams
  INTRODUCTION currents associated with the continuous operation of fixed
  frequency designs. Gated oscillator regulators simply
  self-clock at whatever frequency is required to maintain
  the output voltage. Typically, loop oscillation frequency
  ranges from a few hertz into the kilohertz region, depending upon the load. This collection of circuits was worked out between June
  1991 and July of 1994. Most were designed at customer
  request or are derivatives of such efforts. All represent
  substantial effort and, as such, are disseminated here
  for wider study and (hopefully) use.1 The examples are
  roughly arranged in categories including power conversion, transducer signal conditioning, amplifiers and signal
  generators. As always, reader comment and questions
  concerning variants of the circuits shown may be addressed
  directly to the author. In most cases this asynchronous, variable frequency operation does not create problems. Some systems, however, are
  sensitive to this characteristic. Figure 1 slightly modifies
  a gated oscillator type switching regulator by synchronizing its loop oscillation frequency to the systems clock. In
  this fashion the oscillation frequency and its attendant
  switching noise, albeit variable, become coherent with
  system operation. Clock Synchronized Switching Regulator …

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  A Fourth Generation of LCD Backlight Technology &mdash AN65
  PDF, 5.9 Mb, Datei veröffentlicht: Nov 1, 1995
  This publication, LTC's fourth effort devoted to LCD backlighting in as many years, treats the subject comprehensively. The text considers lamps, display and layout induced losses, circuitry, efficiency related issues, optimization and measurement techniques. Twelve appended sections cover lamp types, mechanical design, electrical and photometric measurement, layout, circuitry and related topics.
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  Application Note 65
  November 1995
  A Fourth Generation of LCD Backlight Technology
  Component and Measurement Improvements Refine Performance
  Jim Williams PREFACE
  Current generation portable computers and instruments
  utilize backlit LCDs (liquid crystal displays). These displays
  have also appeared in applications ranging from medical
  equipment to automobiles, gas pumps and retail terminals.
  Cold cathode fluorescent lamps (CCFLs) provide the highest available efficiency for backlighting the display. These
  lamps require high voltage AC to operate, mandating an
  efficient high voltage DC/AC converter. In addition to good
  efficiency, the converter should deliver the lamp drive in
  sine wave form. This is desirable to minimize RF emissions.
  Such emissions can cause interference with other devices,
  as well as degrading overall operating efficiency. The sine
  wave excitation also provides optimal current-to-light
  conversion in the lamp. The circuit should permit lamp
  control from zero to full brightness with no hysteresis or
  “pop-on,” and must also regulate lamp intensity vs power
  supply variations.
  The small size and battery-powered operation associated
  with LCD equipped apparatus mandate low component …

Konstruktionshinweise

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  Switching Regulator Allows Alkalines to Replace NiCads &mdash DN41
  PDF, 70 Kb, Datei veröffentlicht: Nov 1, 1990
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  Switching Regulator Allows Alkalines to Replace NiCads
  Design Note 41
  Brian Huffman
  This circuit is a step-up boost type switching regulator.
  It maintains a constant 6V output as battery voltage
  fails. The inductor accumulates energy from the battery when the LTВ®1270 switch pin (VSW ) switches to
  ground and dumps its stored energy to the output
  when the switch pin (VSW ) goes off. The feedback pin
  (VFB) samples the output from the 6.19k-1.62k divider.
  The LT1270’s error amplifier compares the feedback
  pin voltage to its internal 1.24V reference and controls
  the VSW pin switching current, completing a control
  loop. The output voltage can be varied by changing
  the resistor divider ratio. The RC damper on the VC pin
  provides loop frequency compensation. The minimum
  start up voltage for this circuit is 3V. If a 3.3V start up
  voltage is permissible R1 and Q1 can be removed with
  D2 replaced by a short. In many applications it is desirable to substitute nonrechargeable batteries for chargeable types. This capability is necessary when the NiCads can’t be recharged
  or long charge times are unacceptable. Alkaline batteries are an excellent choice in this situation. They are
  readily available and have reasonable energy density.
  Compared to Alkalines, NiCads provide a more stable
  terminal voltage as they discharge. NiCads decay from
  1.3V to 1.0V, while Alkalines drop from 1.5V to 0.8V. …

Artikel

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  Positive-to-Negative Converter Powers В–48V Telecom Circuits &mdash LT Journal
  PDF, 230 Kb, Datei veröffentlicht: May 1, 1998
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  DESIGN IDEAS Positive-to-Negative Converter Powers
  by Mitchell Lee
  –48V Telecom Circuits
  If you’re designing a system that
  interfaces to telecom equipment,
  chances are you’ll need a –48V supply. The circuit in Figure 1 supplies
  up to 6W at –48V and scales to more
  than 12W with higher power components. Based on the CГєk topology,
  the converter exhibits excellent efficiency over a wide range of loading
  conditions (see Figure 2).
  The LT1171’s error amplifier is
  designed for positive-boost applications, and hence its gain and reference
  are of the wrong phase and polarity
  for sensing an inverted output. In this
  application, the error amplifier is sim-ply bypassed and feedback is applied
  at the compensation (VC) pin. Zener
  diode D2 senses the output, pulling
  down on Q1 and the VC pin, in
  response to small increases in output
  voltage. Pulling down on the VC pin
  reduces peak switch current, and
  constitutes negative feedback. If the
  output is a little low, the Zener’s …

Modellreihe

Herstellerklassifikation

• Power Management > Switching Regulator > SEPIC Regulators
• Power Management > Switching Regulator > Step-Up (Boost) Regulators > Internal Power Switch Boost