by Ashok Bindra:
Whether it is used for biasing avalanche photodiodes (APDs) found in optical receivers, driving photoflash tubes in flash cameras, or charging high-voltage capacitors, the need for high-voltage sources continues to grow. Consequently, in battery-powered units where the input supply voltage is low, step-up or boost DC/DC converters are required to generate voltages that can be several times the input. To address these requirements, suppliers such as Analog Devices, Linear Technology, Maxim Integrated, and Micrel Inc., among others, have produced boost converters with output voltages at 70 V and above.
This article examines such solutions and discusses the topologies and techniques used by each to boost output voltages by ratios of 10:1 or better in order to generate high-DC voltages from very-low DC inputs.
DC/DC Converter Topologies and Techniques to Obtain High Boost Ratios – [Link]
By Bill Saltzstein:
Switching DC/DC power supplies and regulators, regardless of whether IC, module, or chassis, are generally preferred over linear supplies, and with good reason. In general, they are much more efficient, resulting in reduced power use and cost, longer run time, and less heat to dissipate. (Note: There are cases where the linear supply may be more efficient, especially when the input/output voltage differential is small.¹)
However, there is a problem with switching supplies which affects many designs. Due to their inherent internal switching action, they generate more noise than linear supplies. The noise frequency is a function of the underlying switching frequency, which typically is between 100 kHz and several MHz, depending on design and application, and includes several harmonics.
Using Spread-Spectrum Techniques to Manage Switching Power Supply EMI – [Link]
This article shows how to produce negative output voltages from positive input voltages using the MAX17501 and MAX17502 synchronous step-down converters. By Dipankar Mitra:
Industrial control equipment such as programmable logic controllers, I/O modules, mass flow controllers, and various other sensors and supporting systems use analog components like amplifiers and multiplexers that operate on negative supply voltage. Typically operating at ±12V, ±18V or other variations, these voltages are generated from a 24V DC bus. Maxim’s portfolio of high-voltage synchronous buck regulators offer 50% lower power loss allowing customers to operate their equipment 50% cooler. In this application note, we discuss techniques to use these synchronous buck regulators to generate negative voltages.
AppNote: How to Use the MAX17501 and MAX17502 for Negative Output Voltage Applications – [Link]
by Charlie Zhao:
The trend in automobiles and industrial systems is to replace mechanical functions with electronics, thus multiplying the number of microcontrollers, signal processors, sensors, and other electronic devices throughout. The issue is that 24V truck electrical systems and industrial equipment use relatively high voltages for motors and solenoids while the microcontrollers and other electronics require much lower voltages. As a result, there is a clear need for compact, high efficiency step-down converters that can produce very low voltages from the high input voltages.
LTC Design Note: 65V 500mA step-down converter – [Link]
Tutorial – MicroLipo and MiniLipo Battery Chargers @ The Adafruit Learning System.
Sooner or later you’ll need to cut the cord…the power cord! Untether your electronic project from the tyranny of the wall adapter and take it out into the world. That’s where batteries come in, and you may have been seduced by the high power density, large current capabilites and recharge-ability of Lithium Polymer or Lithium Ion batteries. These battery chemistries have quickly become the most popular rechargeable batteries in consumer products, powering everything from keychain mp3 players to huge laptops.
Tutorial – MicroLipo and MiniLipo Battery Chargers – [Link]
by Ken Shirriff:
Disassembling Apple’s diminutive inch-cube iPhone charger reveals a technologically advanced flyback switching power supply that goes beyond the typical charger. It simply takes AC input (anything between 100 and 240 volts) and produce 5 watts of smooth 5 volt power, but the circuit to do this is surprisingly complex and innovative.
Apple iPhone charger teardown – [Link]
The Joule thief is a really fascinating circuit, simple yet very intricate. Basically, it’s a step-up converted in its most elementary expression. I will spare you the theory since there is plenty of information on it on the web; rustybolt.info is a good place to start.
Joule thieves in all sorts of forms have been featured countless time on DIY websites and I felt it was time I build one. However, I did not want to leave the circuit at the breadboard stage because as it stands, the joule thief has characteristics that make it very attractive for all sorts of low power applications and I figured a flash light would be a very good home for a joule thief, where having the option of using dead batteries is certainly a big plus not to mention using less cells because the circuit steps the voltage up. Why dead batteries? Because a battery is never really dead, its voltage just falls down logarithmically until it hits a point where the device it was powering up stops functioning, which does not mean the battery is totally drained but rather that its voltage has fallen below a usable level. Since joule thieves are step-up converters, they can take that “dead” battery, and give it a new life by stepping up its output voltage to usable levels again.
Maglite Joule thief – [Link]
By Tahar Allag, Wenjia Liu:
Cell phones are a good example of how functionality and performance have both increased significantly in portable devices over the last few decades. They have become more complex and can do many basic tasks as well as any computer. The extra functionality that has transitioned the smartphone from a phone-call-only device to a multipurpose portable device, which makes it more power hungry than ever before.
The internal battery pack is the main source of storing and delivering power to portable-device circuitry. Batterycharger ICs are responsible for charging the battery pack safely and efficiently. They must also control the power delivery to the system to maintain normal operation while plugged in to wall power. The battery pack is required to store a large amount of energy and be charged in a short amount of time without sacrificing weight and volume. The increased charge and discharge currents, as well as the smaller physical size, make the packs vulnerable to physical and thermal stresses. Therefore, battery chargers are no longer required to perform just as a simple standalone charger
AppNote: Battery charging considerations for high-power portabledevices – [Link]
Designers of rechargeable battery-powered equipment want a charger that minimizes charge time with maximum charge current by maximizing the power taken from the supply without collapsing the supply. Resistances between the supply and the battery present a challenge. This article explains how to design the charging circuit to achieve the maximum power from the adapter despite the undesired resistances between the supply and battery.
AppNote: Extract maximum power from the supply when charging a battery – [Link]