Generate an Output Below the Reference Voltage
Oct 1, 2007
Applications sometimes require the generation of a voltage that is below the reference rail. Many design engineers would just use a second regulator to generate this voltage. However, a simple change in the feedback path of a switching regulator allows a single regulator to perform this task....
Controller Monitors ORing FET Current and Voltage
Sep 1, 2007
Power supplies with N+1 redundancy require the use of an ORing diode or FET to isolate the main supply from the output bus in case of failure. Although ORing diodes are easy to use, the power loss they would cause in high-current supplies is usually unacceptable....
Negative Supply Uses Positive Hysteretic Regulator
Aug 1, 2007
Frequently, the use of a hysteretic regulator is preferred because of its simplicity of use and wide input-voltage range. For example, National Semiconductor's LM5007 is a constant-on-time variation of the hysteretic topology, but offers a nearly constant frequency of operation....
Power Multiplexer Prevents Cross-Current Conduction
May 1, 2007
Many systems require a power multiplexer to select between two different power sources. For example, a PCI-based board needs to be able to select between...
A Simple Latching Watchdog Timer
Apr 1, 2007
Most watchdog-timer ICs produce a single limited-duration output pulse when the watchdog timeout expires. Some applications, however, require the output to latch. This simple circuit provides a latched failure indication in response to a loss of the input pulse stream....
Discrete Circuit Protects Li-Ion Battery Charger
Mar 1, 2007
Many battery-powered applications use diodes for reverse-battery protection. However, a diode does not always protect a battery charger when the battery is inserted incorrectly. Sometimes when the battery is inserted backwards, it can cause a large amount of current flow through the charging circuitry, potentially destroying both the battery and the charger. ...
Voltage Detector Provides Sensitivity and Precision
Feb 1, 2007
A function often needed in industrial and scientific applications is detecting the presence - or absence - of dc voltages in such components as safety interlocks and automatic sequencers....
LED Balancing Circuit With Power Limit
Jan 1, 2007
Light-emitting diodes are often used with a voltage source from a power-supply output voltage. The output voltage increases until the current through the LEDs reaches the value of the constant-current source from the power supply....
Bootstrap Feedback Linearizes Current Source
Nov 1, 2006
Adjustable current sources often exhibit a nonlinear
control characteristic, but the inclusion of bootstrap feedback provides an inherently linear control that works well at all levels of
output current....
Ultracapacitors Boost Battery in Power Tools
Oct 1, 2006
In portable applications where battery life is important, designers may evaluate various battery chemistries to determine the best energy source. For...
USB Port Powers Bipolar Supply
Sep 1, 2006
The USB port on most personal computers can be a handy source of power. It is not allowed to deliver the maximum specified current (500 mA) without software...
Slope Compensation for Mild Inductor Saturation
Aug 1, 2006
Peak current control has long been a popular PWM method in switching power supplies and has the equally well-known characteristic that when operating in continuous conduction mode...
MOV and PPTC Devices Enable IEC 61000-4-5 Compliance
Jul 1, 2006
Coordinating overcurrent and overvoltage protection at the ac mains input can help designers comply with safety agency requirements, minimize component count and cost...
High-Side Current Amplifier Forms 28-V Circuit Breaker
Jun 1, 2006
The latching-comparator output (COUT1) on the MAX4373, a high-side current amplifier with comparator and voltage reference, makes possible a circuit-breaker...
Performing Thermal Analysis in System
May 1, 2006
Integrated circuit (IC) manufacturers normally publish a thermal resistance rating ( thermal resistance from die junction-to-ambient air) on their data...
PolySwitch Device Enhances Overcurrent Protection
Apr 1, 2006
Where resettable overcurrent protection is a requirement, PolySwitch polymeric positive temperature coefficient (PPTC) devices offer a highly effective...
Low-Cost Microcontroller Dithers Switching Frequency
Mar 1, 2006
Because of the high level of output power that switching power-supply designs have, systems designers are challenged to develop designs that meet consumer...
Filter Senses Current in High-Voltage Motor Drives
Feb 1, 2006
Traditional motor-phase-current sensing methods depend on sensors with signal bandwidths of 100 kHz or greater. Problematically, such bandwidths allow...
Small MOSFETs Solve Big Problems
Jan 1, 2006
Synchronous rectification has become the standard for high-efficiency power converters. The perpetually decreasing supply voltages that are required by...
Determining Power Dissipation Range of Charger IC
Nov 1, 2005
Today, many portable applications come equipped with Li-ion and Li-polymer batteries, since they provide a very high-energy density relative to their...
Latched Overcurrent Fault Detector Has Fast Response Time
Oct 1, 2005
OVERCURRENT DETECTOR - the circuit introduced here is a simple and fast-responding overcurrent detector for protection of low-voltage applications. Unlike dedicated hot-swap controllers that impose a long startup delay initiated by undervoltage, this circuit provides protection only 150 µs after the input supply rises above 2.7 V. It also possesses a measure of inrush current limiting during power up, by virtue of the limited gate voltage on an external p-channel switch....
Precision Circuit Monitors Negative Supply Current
Sep 1, 2005
Supply-current monitoring is a necessary feature in high-reliability systems for which excessive current can cause damage or compromise safety. Such systems...
Bootstrap Circuit for Green-Mode Standards
Aug 1, 2005
To conserve energy, there has been a big push to lower the standby power in off-line power supplies. Many countries around the world are adopting green-mode...
Add a Watchdog to a Dual-Output Power Supply
Jul 1, 2005
The design of low-cost consumer products like set-top boxes and DSL modems often requires a main logic supply in addition to the core voltage, so the...
Back to the Future with Magnetic Modulation
Jun 1, 2005
More than two decades ago, I was responsible for developing the two ac-dc power supplies that would ultimately be used in the AN/ALQ-184 Radar Jammer...
