5A and 2.5A High Efficiency Switching Regulators
PDF, 656 Kb, Language: en, File published: Jun 1, 1986, Pages: 80
Application Note 19. This design manual is an extensive discussion of all standard switching configurations for the LT1070; including buck, boost, flyback, forward, inverting and "Cuk." The manual includes comprehensive information on the LT1070, the external components used with it, and complete formulas for calculating component values.
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Application Note 19
June 1986
LT1070 Design Manual
Carl Nelson
INTRODUCTION
Three terminal monolithic linear voltage regulators appeared almost 20 years ago, and were almost immediately
successful for a variety of reasons. In particular, there
were relatively few engineers capable of designing a good
linear voltage regulator. The new devices were also easy to
use, and inexpensive. In currently popular parlance they
were "expert systems," containing a good deal of their
designer's knowledge in silicon form. Because of these
advantages, the regulators quickly eclipsed discrete and
earlier monolithic building blocks and dominated the
market.
More recently, there has been increasing interest in switching-based regulators. Switching regulators, with their
high efficiency and small size, are increasingly desirable
as overall package sizes have shrunk. Unfortunately, switching regulators are also one of the most difficult linear
circuits to design. Mysterious modes, sudden failures,
peculiar regulation characteristics and just plain explosions are common occurrences during the design of a
switching regulator.
Most switching regulator ICs are building blocks. Many
discrete components are required, and substantial expertise is assumed on the part of the user. Some newer
…
PDF, 359 Kb, File published: Sep 2, 1987
Subtitled "A Gentle Guide for the Trepidatious," this is a tutorial on switching regulator design. The text assumes no switching regulator design experience, contains no equations, and requires no inductor construction to build the circuits described. Designs detailed include flyback, isolated telecom, off-line, and others. Appended sections cover component considerations, measurement techniques and steps involved in developing a working circuit.
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Application Note 25
September 1987 Switching Regulators for Poets
A Gentle Guide for the Trepidatious
Jim Williams
The above title is not happenstance and was arrived at after
considerable deliberation. As a linear IC manufacturer, it is
our goal to encourage users to design and build switching
regulators. A problem is that while everyone agrees that
working switching regulators are a good thing, everyone
also agrees that they are difficult to get working. Switching
regulators, with their high efficiency and small size, are
increasingly desirable as overall package sizes shrink.
Unfortunately, switching regulators are also one of the
most difficult linear circuits to design. Mysterious modes,
sudden, seemingly inexplicable failures, peculiar regulation characteristics and just plain explosions are common
occurrences. Diodes conduct the wrong way. Things get
hot that shouldn’t. Capacitors act like resistors, fuses
don’t blow and transistors do. The output is at ground, and
the ground terminal shows volts of noise.
Added to this poisonous brew is the regulator’s feedback
loop, sampled in nature and replete with uncertain phase
shifts. Everything, of course, varies with line and load
conditions— and the time of day, or so it seems. In the face …
PDF, 1.2 Mb, File published: Oct 1, 1988
This note examines a wide range of DC/DC converter applications. Single inductor, transformer, and switched-capacitor converter designs are shown. Special topics like low noise, high efficiency, low quiescent current, high voltage, and wide-input voltage range converters are covered. Appended sections explain some fundamental properties of different types of converters.
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Application Note 29
October 1988
Some Thoughts on DC/DC Converters
Jim Williams and Brian Huffman
INTRODUCTION
Many systems require that the primary source of DC power
be converted to other voltages. Battery driven circuitry is
an obvious candidate. The 6V or 12V cell in a laptop computer must be converted to different potentials needed for
memory, disc drives, display and operating logic. In theory,
AC line powered systems should not need DC/DC converters
because the implied power transformer can be equipped
with multiple secondaries. In practice, economics, noise
requirements, supply bus distribution problems and other
constraints often make DC/DC conversion preferable. A
common example is logic dominated, 5V powered systems
utilizing В±15V driven analog components.
The range of applications for DC/DC converters is large,
with many variations. Interest in converters is commensurately quite high. Increased use of single supply powered
systems, stiffening performance requirements and battery
operation have increased converter usage.
Historically, efficiency and size have received heavy emphasis. In fact, these parameters can be significant, but
often are of secondary importance. A possible reason
behind the continued and overwhelming attention to size …
PDF, 606 Kb, File published: Feb 1, 1989
Switching regulators are of universal interest. Linear Technology has made a major effort to address this topic. A catalog of circuits has been compiled so that a design engineer can swiftly determine which converter type is best. This catalog serves as a visual index to be browsed through for a specific or general interest.
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Application Note 30
February 1989
Switching Regulator Circuit Collection
John Seago
Switching regulators are of universal interest. Linear
Technology has made a major effort to address this topic.
A catalog of circuits has been compiled so that a design
engineer can swiftly determine which converter type is
best. This catalog serves as a visual index to be browsed
through for a specific or general interest. The catalog is organized so that converter topologies can
be easily found. There are 12 basic circuit categories:
Battery, Boost, Buck, Buck-Boost, Flyback, Forward, High
Voltage, Multioutput, Off Line, Preregulator, Switched
Capacitor and Telecom. Additional circuit information can
be located in the references listed in the index. The
reference works as follows, i.e., AN8, Page 2 = Application
Note 8, Page 2; LTC1044 DS = LTC1044 data sheet;
DN17 = Design Note 17. DRAWING INDEX
FIGURE TITLE FIGURE # PAGE REFERENCE/SOURCE Battery
2A Converter with 150ВµA Quiescent Current (6V to 12V)
200mA Output Converter (1.5V to 5V)
Up Converter (6V to 15V)
Regulated Up Converter (5V to 10V) …
PDF, 1.5 Mb, File published: Feb 2, 1989
Subtitled "Some Affable Analogs for Digital Devotees," discusses a number of analog circuits useful in predominantly digital systems. VPP generators for flash memories receive extensive treatment. Other examples include a current loop transmitter, dropout detectors, power management circuits, and clocks.
PDF, 6.2 Mb, File published: Aug 1, 1989
Discusses the LT1074, an easily applied step-down regulator IC. Basic concepts and circuits are described along with more sophisticated applications. Six appended sections cover LT1074 circuitry detail, inductor and discrete component selection, current measuring techniques, efficiency considerations and other topics.
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Application Note 35
August 1989
Step-Down Switching Regulators
Jim Williams
lost in this voltage-to-current-to-magnetic п¬Ѓeld-to-current-to-charge-to-voltage conversion. In practice, the
circuit elements have losses, but step-down efficiency is
still higher than with inherently dissipative (e.g., voltage
divider) approaches. Figure 2 feedback controls the basic
circuit to regulate output voltage. In this case switch ontime (e.g., inductor charge time) is varied to maintain the
output against changes in input or loading.
REGULATED
OUTPUT IN PULSE
WIDTH
MODULATOR Figure 1 is a conceptual voltage step-down or “buck”
circuit. When the switch closes the input voltage appears
at the inductor. Current flowing through the inductor-capacitor combination builds over time. When the switch
IN OUT AN35 F01 Figure 1. Conceptual Voltage Step-Down (“Buck”) Circuit opens current flow ceases and the magnetic field around
the inductor collapses. Faraday teaches that the voltage
induced by the collapsing magnetic п¬Ѓeld is opposite to the
originally applied voltage. As such, the inductor’s left side
heads negative and is clamped by the diode. The capacitors accumulated charge has no discharge path, and a DC
potential appears at the output. This DC potential is lower
than the input because the inductor limits current during …
PDF, 764 Kb, File published: Feb 3, 1990
This note explores the causes of the large resonating current spikes on the leading edge of the switch current waveform. These anomalies are exacerbated in very high voltage designs.
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Application Note 39
February 1990
Parasitic Capacitance Effects
in Step-Up Transformer Design
Brian Huffman
One of the most critical components in a step-up design
like Figure 1 is the transformer. Transformers have parasitic components that can cause them to deviate from
their ideal characteristics, and the parasitic capacitance
associated with the secondary can cause large resonating
current spikes on the leading edge of the switch current
waveform. These spikes can cause the regulator to exhibit
erratic operating conditions that manifests itself as duty
cycle instability. This effect is exacerbated in very high
voltage designs. Attention to transformer design will cure
this problem. Figure 2 shows the high frequency current paths of the
parasitic capacitors. In the analysis of operation assume
the input and output voltages are at AC ground. Thus, the
parasitic capacitors are all in parallel. The transformer’s
secondary provides the AC current path for these capacitors. The current flowing through the secondary produces
N times the current in the primary. As the parasitic capacitance and turns ratio increase, the primary current
becomes progressively larger. D1
MUR1100
VIN …
PDF, 477 Kb, File published: Sep 1, 1991
This note discusses the use of the LT1074 and LT1076 high efficiency switching regulators. These regulators are specifically designed for ease of use. This application note is intended to eliminate the most common errors that customers make when using switching regulators as well as offering insight into the inner workings of switching designs. There is an entirely new treatment of inductor design based upon simple mathematical formulas that yield direct results. There are extensive tutorial sections devoted to the care and feeding of the Positive Step- Down (Buck) Converter, the Tapped Inductor Buck Converter, the Positive-to-Negative Converter and the Negative Boost Converter. Additionally, many troubleshooting hints are included as well as oscilloscope techniques, soft-start architectures, and micropower shutdown and EMI suppression methods.
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Application Note 44
September 1991
LT1074/LT1076 Design Manual
Carl Nelson
INTRODUCTION
The use of switching regulators increased dramatically in
the 1980’s and this trend remains strong going into the
90s. The reasons for this are simple; heat and efficiency.
Today’s systems are shrinking continuously, while simultaneously offering greater electronic “horsepower.” This
combination would result in unacceptably high internal
temperatures if low efficiency linear supplies were used.
Heat sinks do not solve the problem in general because
most systems are closed, with low thermal transfer from
“inside” to “outside.”
Battery-powered systems need high efficiency supplies for
long battery life. Topological considerations also require
switching technology. For instance, a battery cannot
generate an output higher than itself with linear supplies.
The availability of low cost rechargeable batteries has created a spectacular rise in the number of battery-powered
systems, and consequently a matching rise in the use of
switching regulators.
The LTВ®1074 and LT1076 switching regulators are designed
specifically for ease of use. They are close to the ultimate …
PDF, 2.6 Mb, File published: Nov 1, 1991
Efficiency varies for different DC/DC converters. This application note compares the efficiency characteristics of some of the more popular types. Step-up, step-down, flyback, negative-to-positive, and positive-to-negative are shown. Appended sections discuss how to select the proper aluminum electrolytic capacitor and explain power switch and output diode loss calculations.
PDF, 95 Kb, File published: Jun 1, 1988
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advertisement Achieving Microamp Quiescent Current in Switching Regulators
Design Note 11
Jim Williams
Many battery powered applications require very wide
ranges of power supply output current. Normal conditions require currents in the ampere range, while
standby or “sleep” modes draw only microamperes.
A typical lap top computer may draw 1 to 2 amperes
running while needing only a few hundred microamps
for memory when turned off. In theory, any switching
regulator designed for loop stability under no-load
conditions will work. In practice, a regulator’s relatively
large quiescent current may cause unacceptable battery
drain during low output current intervals.
Figure 1 shows a typical flyback regulator. In this
case the 6V battery is converted to a 12V output by
the inductive flyback voltage produced each time the
LT®1070’s VSW pin is internally switched to ground. An
internal 40kHz clock produces a flyback event every
25μs. The energy in this event is controlled by the IC’s
internal error amplifier, which acts to force the feedback
(FB) pin to a 1.23V reference. The error amplifiers high
impedance output (the VC pin) uses an RC damper for
stable loop compensation. …
PDF, 80 Kb, File published: Aug 1, 1996
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Telephone Ring-Tone Generation – Design Note 134
Dale Eagar
Requirements
When your telephone rings, exactly what is the phone
company doing? This question comes up frequently, as
it seems everyone is becoming a telephone company.
Deregulation opens many new opportunities, but if you
want to be the phone company you have to ring bells.
An Open-Architecture Ring-Tone Generator
Here is a design that you can own, tailor to your specific
needs, layout on your circuit board and put on your bill
of materials. Finally, you will be in control of the black
magic (and high voltages) of ring-tone generation.
Not Your Standard Bench Supply
Ring-tone generation requires not one but two high
voltages, 60VDC and – 180VDC (this arises from the
need to put 87VRMS on –48VDC). Figure 1 details the
switching power supply that delivers the volts needed
to run the ring-tone circuit. This switcher can be powered from any voltage from 5V to 30V and shuts down
when not in use. Figure 2 is the build diagram of the
transformer used in the switching power supply.
60V
MUR160 = PRIMARY GROUND T1 2 = SECONDARY GROUND + …
PDF, 90 Kb, File published: Dec 1, 1988
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A Battery Powered Lap Top Computer Power Supply
Design Note 18
Brian Huffman
Most battery powered lap top computers require regulated multiple output potentials. Problems associated
with such a supply include magnetic and snubber design,
loop compensation, short circuit protection, size and
efficiency. Typical output power requirements include
5V @ 1A for memory and logic circuitry and В±12V
@ 300mA to drive the analog components. Primary
power may be either a 6V or 12V battery. The circuit
in Figure 1 meets all these requirements. The LTВ®1071
simplifies the power supply design by integrating most
of the switching regulator building blocks. Also, the
off-the-shelf transformer eliminates all the headaches
associated with the magnetic design.
The circuit is a basic flyback regulator. The transformer
transfers the energy from the 12V input to the 5V and
В±12V outputs. Figure 2 shows the voltage (trace A) and
the current (trace B) waveforms at the VSW pin. The
VSW output is a collector of a common emitter NPN,
so current flows through it when it is low. The circuit’s
40kHz repetition rate is set by the LT1071’s internal
oscillator. During the VSW (trace A) “on” time, the input …
PDF, 71 Kb, File published: Apr 1, 1989
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advertisement Floating Input Extends Regulator Capabilities – Design Note 21
Brian Huffman
however, if the secondary windings are isolated from
one another, a low dropout positive voltage regulator
can be used for negative regulation (Figure 1). Many applications require circuit performance that is
unachievable with conventional regulator design. This
results in added complexity to the circuit. However, some
problems can easily be solved by floating the input to
the regulator. A floating input can either be a battery, or
a secondary winding that is galvanically isolated from
all other windings. With this method high efficiency
negative voltage regulation, high voltage regulation, and
low saturation loss positive buck switching regulator
can all be achieved easily. In this circuit the LTВ®1086 servos the voltage between
the output and the adjust pin to 1.25V. The positive
regulation is accomplished by conventional regulator
design. Negative voltage regulation is achieved by
connecting the output of the positive voltage regulator
to ground. The VIN pin floats to 1.5V or greater, above
ground. This technique can be used with any positive
voltage regulator, although highest efficiency occurs
with low dropout types. Low dropout negative voltage regulators are not currently available. This would seem to preclude high efficiency negative linear regulators. Such regulation is
frequently desired in switching supply post regulators; L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks …
PDF, 114 Kb, File published: Mar 1, 1988
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advertisement Inductor Selection for Switching Regulators
Design Note 8
Jim Williams
A common problem area in switching regulator design
is the inductor, and the most common difficulty is
saturation. An inductor is saturated when it cannot
hold any more magnetic flux. As an inductor arrives
at saturation it begins to look more resistive and less
inductive. Under these conditions current flow is limited
only by the inductor’s DC copper resistance and the
source capacity. This is why saturation often results
in destructive failures.
While saturation is a prime concern, cost, heating,
size, availability and desired performance are also
significant. Electromagnetic theory, although applicable
to these issues, can be confusing, particularly to the
non-specialist.
Practically speaking, an empirical approach is often a
good way to approach inductor selection. It permits real time analysis under actual circuit operating conditions
using the ultimate simulator—a breadboard. If desired,
inductor design theory can be used to augment or
confirm experimental results.
Figure 1 shows a typical flyback regulator utilizing the …
