General power supply design information
- 1.5 V: This is the voltage you get from one battery cell.
- 3 V: This is a voltage you get from two normal battery cells. This voltage is usually used in small devices that operate at two AA batteries.
- 3.3 V: This is the voltage used in many modern logic IC designs. This voltage is used in the most modern computer digital electronics.
- 4.5 V: This is the voltage you get from three battery cells in series.
- 5 V: This is the voltage used in TTL logic ICs. This voltage is found inside most computers.
- 6.0 V: This is the voltage you get from four battery cells in series. Many small electronic battery operated appliances operate at this voltage.
- 9 V: This a voltage used in many small electronics applicances, for example majority of multimeters and other small handled test instruments. The power for this kind of devices is normally taken from 9V battery. Also very many small "electronics gadgets" are powered from 9V DC "wall warts".
- 12 V: This is the voltage used in typical car electrical and boat system. This is also used inside computer and such for powering high power loads like disk drives. Also very many small "electronics gadgets" are powered from 12V DC "wall warts".
- 15 V: Bipolar +-15V power supply is a very common voltage used in audio electronics circuits that use operational amplifiers.
- 24 V: This is the voltage used in truck electrical system and for powering industrial automation systems. In industrial autiomation systems devices like relay coils, process controllers, PLCs and current loop interfaces are powered with this voltage. Some distributed power system use this voltage as the distributed voltage.
- 36 V: This voltage is used by some battery powered small moving devices. The power is taken from three series connected 12V batteries. 36V battery systems are also coming to new cars.
- 48 V: This is the classical telecom world woltage. Battery backed up -48V (negative compared to ground) powers the telephone exhanges and other telephone network devices. This is also the voltage supplied to a normal telephone line by the telephone central. +48V is used in audio world as the standard voltage for phantom power supply that is supplied by many professional audio mixers to power microphones and DI-boxes through mixer microphone wiring.
- 60 V: This is the highest "safe" DC voltage (this is the Safety Extra Low Voltage limit). A system/wiring that carries anything higher than is considered to carry "dangrous voltage" and should be constructed in very safe ways (like mains voltage wiring). Some telecom systems use 60V voltage (60V is quite rarely used, 48V is far more common in telecom world).
- 90 V: This is a voltage used in telecom world in applications where quite a bit of power needs bo be transpowerted through long thin wires (through telephone loop). This voltage is used by some telecom signal amplifier, repeaters and some line powered ISDN system components.
- 120 V: This is used in some automation systems for controlling heavier loads that can be controlled with 24V DC.
- 320 V: This is the typical average voltage (can vary somewhat) found in mains powered switched mode power supply after the incoming 230V mains voltage is rectified and filtered (many switchable 230/110V AC input switchers multiply the incoming voltage by two when switched to 110V mode to get this 320V voltage as result).
- Ceramic capacitors in dc/dc-input filters: OK, but watch out for those transients - Designers now have new reasons to use ceramic, rather than tantalum, capacitors. But be careful. Rate this link
- Choosing a heat sink: some tips and recommendations - There can be a bit more to choosing a heat sink than you might think. You need to consider thermal performance in addition to a variety of physical configurations. Rate this link
- Design guidelines help dc/dc converters work properly over long lines - some background and design tips help ensure optimum converter operation under various long line conditions Rate this link
- Designing Power Supplies the Easy Way - Very High Voltage ICs, or VHVICs, make designing a power supply easy Rate this link
- Feedback isolation augments power-supply safety and performance - properly designed isolated feedback is crucial to maintaining safety on many power supply designs Rate this link
- Just-In-Time Power Supply Design - just-in-time power supply design is increasingly untenable because simple power supply is not so simple anymore Rate this link
- Linear Supplies feel the (lack of) heat from switchers in low-wattage applications - ICs that implement advanced supply techniques are challenging linear supplies by lowering costs, cutting size, and increasing efficiency Rate this link
- Linear Supplies feel the (lack of) heat from switchers in low-wattage applications - ICs that implement advanced supply techniques are challenging linear supplies by lowering costs, cutting size, and increasing efficiency. Rate this link
- Linear vs Switching Supplies: Weighing All the Options - the choice between linear and switching board-level power supplies is sometimes clear-cut but can be sometimes hard to do Rate this link
- Power Conversion in Line-Powered Equipment - application note in pdf format Rate this link
- Power.national.com - collection of power supply design information from National Semiconductor Rate this link
- Powering the big microprocessors - modern microprocessor power-supply design must furnish many amps at a tightly controlled voltage level and respond quickly to heavy load transients Rate this link
- Power-supply reliability: a practical improvement guide - path to high reliability is a well-managed process that starts in the product's definition phase and continues long after the first shipment Rate this link
- Principles of Power Conversion - The advent and widespread availability of reliable and efficient standard power modules has drastically changed the focus of the power system designer. Most of the converter topology choices will be transparent to the end user - that is, the specifications of the module and its performance in the end system will not be affected. There are some choices, however, that will affect performance and the system designer should be familiar with these considerations. Rate this link
- Proper layout and component selection control power-supply EMI - All power-supply components, including voltage regulators, inductors, and transformers, and their layout determine the amount of EMI a supply generates. An overview covers the mechanisms and physical principles governing the generation and propagation of power-supply electrical noise. Rate this link
- Truth or Consequences of LDO Regulators - low-dropout regulator, better known as LDO, is a special type of regulator where the minimum required voltage between the input-output voltage (the dropout voltage) is significantly smaller than predecessor parts Rate this link
- Using thermistors in temperature-tracking power supplies - Simple linearizing schemes make it easy to use thermistors to implement voltage-regulator designs with temperature-dependent outputs. Rate this link
- Minimize the short-circuit current pulse in a hot-swap controller - Because of internal circuit-breaker delay and limited MOS-gate pulldown current, many hot-swap controllers do not limit current during the first 10 to 50 ?sec following a shorted output. The result can be a brief flow of several hundred amperes. A simple external circuit can counter this problem by minimizing the initial current spike and terminating the short circuit within 200 to 500 nsec. Rate this link
- DC-DC Converters Deliver Better Performance For Distributed Power - with their enhanced efficiency and features, modular components deliver high currents and low voltages, in small packages Rate this link
- Decoupling capacitors: use them or fail - Theory is wonderful, but practicalities have their place. This rule is to use one 0.1-?F ceramic per digital chip, two 0.1-?F ceramics per analog chip (one on each supply), and one 1-?F tantalum per every eight ICs or per IC row. Rate this link
- Distributed power takes center stage - distributed power has become a strategic architecture for digital systems Rate this link
- Distributed power: taming the dragons - New architectures and packaging are teaming to tame the tiny voltage drops that so easily spell disaster in systems whose supply voltages will soon be measured in mere millivolts. Rate this link
- Good design enables hot insertion of power supplies - hot insertion of power supplies offers many advantages, but it can cause lots of problems unless you prepare for it in your design Rate this link
- High-Density Power Components Add Flexibility To Distributed-Power Design - correct load partitioning, thermal management, and filtering help to achieve successful distributed-power solutions Rate this link
- High-end digital systems give a thumbs down to rules of thumb - lower voltages, higher current transients, and higher clock rates render rules of thumb uselsss for designing power-distribution-system decoupling networks Rate this link
- Hot-swapping power - Hot-swap power controllers can make the difference between a product that lasts long enough to be a classic and one that's just a bus crash waiting to happen. Rate this link
- Hot-swap your way to high availability - follow live-insertion board-design guidelines to keep the sparks from flying Rate this link
- Packaged DC-DC Converters Solve Distributed Power Dilemmas when used properly, off-the-shelf, isolated dc-dc converters save space, reduce component count, and simplify design Rate this link
- Simple Techniques Minimize Cross-Coupling in Distributed Power Systems Rate this link
- Use local bypass capacitors to meet rigorous high-speed-system demands - When conductors look like inductors and supply lines must absorb amps of fast-edge glitchiness, low-inductance, locally applied bypass capacitors come to the rescue. Rate this link
- For very small power supplies (a few watts at most) adding a resistor in series with the line is a simple and practical solution to limit the inrush current, but will cause loss in efficiency.
- Many power-supply manufacturers use a negative temperature coefficient (NTC) resistor in series with the line. An NTC resistor offers tens of ohms of resistance when cool, dropping to less than one ohm as its temperature increases. If the power supply is cool when turned on, the NTC provides good inrush-current limiting (but not when user turns the system off and then immediately switches it back on).
- Placing a relay or electronic switch in parallel with either a resistor or NTC can offer high impedance only at startup. This kind of circuit must be designed in such way that the resistor does not burn up during brown-outs.
- A control circuit can use a zero-crossing techniques to monitor the ac line and turn on the power supply only when the input line is low.
- Many larger power switch mode supplies use an active power factor correction circuit in front of the main switcher circuit. Some active power factor correction circutis can be designed in such way that they provide a soft-start.
- Plug in: Safeguard ac powerline quality - Today's proliferation of electronics creates power-quality problems that are sufficiently severe to attract regulatory action. Rate this link
- Active power factor correction - Until recently, virtually any domestic appliance you switched on looked very much like a resistor to the ac line supply. The explosive growth in consumer electronics has radically changed this picture, and it's causing the electricity supply industry considerable concern. Rate this link
- Devices clean up power factor in ac/dc supplies - Power-factor correction is a major issue in switching power supplies. Regulator ICs effect the correction and supply many other functions to boot. Rate this link
- Get a (power) line on mysterious malfunctions - technology helps EEs bulletproof new designs against the vicissitudes of the ac line Rate this link
- Compliance Testing to the IEC 1000-3-2 (EN 61000-3-2) and IEC 1000-3-3 (EN 61000-3-3) Standards - Regulatory standards for ac mains phenomena are critical to maintaining the quality of ac power distribution systems. The goal of this application note is to provide an introduction to these standards as well as insight into their scope and intent. An effort has also been made to openly explore the interpretive as well as technical issues of the standards. The discussion of these issues is included to stimulate end-users who test products for compliance to consider both the interpretive and technical merit of test solutions. Rate this link
- Inside a Power-Cube Transformer - How those little things convert mains AC to safe low voltage DC Rate this link
- Power Factor - The purpose of this Tech Note is to clear up a common misunderstanding about the measurement of power in alternating current (AC) circuits. Most people with electrical experience have heard that power equals amps times volts. This is always true for direct current (DC) circuits, but the situation is more complicated with AC circuits. Rate this link
- Power factor: Dissipating the Myths - it is more than just cos(Phi) Rate this link
- Product Safety - connection to external power sources - the implications of hazardous voltages, energy and power Rate this link
- The fuse-selection checklist: a quick update - a fuse-selection checklist now must include the I2t parameter Rate this link
- Plug in: Safeguard ac powerline quality - Today's proliferation of electronics creates power-quality problems that are sufficiently severe to attract regulatory action. With legislation in place within the European Union and the United States and Far East looking to follow, standards provide designers with tools to ensure compliance. Rate this link
- Choosing and Installing Mains Filters - to reduce RF emissions and improve immunity, designers must specify the right filter for the job, article from Rate this link
- Ferroresonant Powering In Today's Broadband Environment - ferroresonant power supplies have been the most widely used powering systems in cable TV Rate this link
- National Semiconductor Webpench Selector for Power Supply ICs - on-line tool for selecting ICs for power supply applications Rate this link
- How to Calculate Voltage Drop For Long Paired Wire Runs - usually primary concern when installing lengths of wire is voltage drop Rate this link
- Automotive Power: Future System Architectures Face Formidable Hurdles - car power systema are moving to higher voltages Rate this link
- Battery Cable Inductance Rate this link
- Smart power switches simplify low-voltage systems - Low-voltage automotive, consumer, and industrial equipment traditionally requires complex analogue circuitry to guarantee load protection. By combining power MOSFETs, gate drivers, and multiple protection circuits in a single package, today?s intelligent power switches simplify the digital-control-to-dc-load connection for current levels reaching more than 100A. Rate this link
- An Almost-Ideal Low-Battery Cut-Off Circuit Draws Only 1.2 ?A - this power-control circuit consumes no power when off, and no voltage drop occurs when the power is on Rate this link
- Choosing a power supply, automatically - Smart power switches provide a way for low-power devices to intelligently switch between power supplies and save power at the same time. Rate this link
- Circuit trade-offs minimize noise in battery-input power supplies - analyzing noise from the perspective of portable-system design will help you make appropriate power-supply design trade-offs Rate this link
- Dynamic voltage scaling conserves portable power - With portable applications on the rise, designers are turning to dynamic power-conservation techniques to delay the inevitable dead battery. Rate this link
- Energy Management for Small Portable Systems - Numerous diverse and conflicting constraints burden the designer of small hand-held products Rate this link
- Live long and prosper: juggling performance and battery life in handheld systems - Look beyond data sheets and examine your hardware design and software environment to ensure optimal performance and power consumption. Rate this link
- Mobile phones put the squeeze on battery power - powering mobile phones from fewer cells focuses attention on every aspect of battery discharge Rate this link
- Portable systems demand vigilant overcurrent protection - modern portable systems require protection from an arsenal of potential overcurrent problems Rate this link
- Power down for portables - A big battery can mean small market share. Reducing power consumption in your portable digital device is the "green" thing to do, as in money. Rate this link
- Pushbutton switch controls power supply and ?C - switching handheld units on and off with a pushbutton switch is a desirable feature but needs some thinking Rate this link
- Remote control turns battery on and off - circuit acts like a latching solid-state relay Rate this link
- Simple regulator monitors its input voltage - portable systems usually monitor their battery input to obtain an early warning of a loss of battery voltage Rate this link
A power supply is a device for the conversion of available power of one set of characteristics to another set of characteristics to meet specified requirements. Typical application of power supplies include to convert raw input power to a controlled or stabilized voltage and/or current for the operation of electronic equipment. Power supplies belong to the field of power electronics, the use of electronics for the control and conversion of electrical power.The simplest unegulated power supply consists of three parts: the transformer, the rectifiers, and the capacitors. This kind of power supply is simple, but the output voltage is not verystable (there can be noticable ripple with the output, and the output voltagechanges with load changed and mains voltage changes).The output voltage can be made more stable by using a more complicatedregulated power supply.The regulated power supply technology can really be divided into two distinct forms; firstly, the linear or series regulator and, secondly, the switched-mode conversion technique. Switched-mode technology is multi-facetted with a wide variety of topologies achieving the end result of providing a regulated DC voltage. The main differences between the linear and switched-mode regulator are in the size, weight and efficiency. The linear regulator utilises simple techniques of controlled energy dissipation to achieve a regulated output voltage independent of line and load variation. It is, therefore, inherently inefficient, especially when a wide input voltage range has to be catered for. Sometimesa power supply is a buffer circuit that provides power with the characteristics required by the load from a primary power source with characteristics incompatible with the load. It makes the load compatible with its power source.A power supply is sometimes called a power converter and the process is called power conversion. It is also sometimes called a power conditioner and the process is called power conditioning. Power supplies should be well designed and protected.Power supply failures can be frustrating, expensive, and time-consuming events because many power supplies are highly complex circuits, with many components operating near the edge of their envelope, and when they fail, they tend to destroy most of the failure evidence with them.There are many different voltage you can encounter in electronics systems and different applications. This list lists some of most commonly used DC voltages you might encounter:
General power supply design
Power distribution from the power source to the place where it is consumed is a challenging task in modern electronics devices which take low voltage (3.3V or 1.8V) and high currents (easily up to tens of ampreres). Distributing high current and low voltages efficiently for long distances is not a good idea. The losses in wiring will be too much. For this reason a distributed power distribution is becoming popular. The idea on this system is that one major power supply generates some intermediate voltage (typically 12 to 40 volts DC) which is distributed around the system. The lower voltages are generated from that power source using local DC/DC converters. The benefir of this approach is that the losses in the power distribution are minimized (higher voltage means less current needed which means less losses in wiring) and it is easy to get stable voltage to output even when there are losses (every local DC/DC converter regulates the outout voltage, so the input voltage for the converter cna vary somewhat with no effect on the DC/DC converter output voltage). In applications where higher voltages are needed, those can also generated with a DC/DC step-up converter. Most typical intermediate voltage system in use are propably 12V DC system used for car electronics and 24V DC system used in industrial electronics. Telecommunication industry has for long time used 48V or 60V battery backed up DC supplies for telecommunication equipment. 12V voltage is becoming popular also in telecommunication systems as the intermediate voltage within the circuit boards. Most computer systems use one of two dc-distribution voltages: 48V and 12V. Those voltages are isolated from the AC line, and both are reasonably well-regulated (typically +-5%). The breakpoint between 12V and 12V usually falls at 1000-1500W power range. Below the breakpoint, 12V dominates. Above the breakpoint, 48V dominates. A few large, high-end systems distribute 400V DC. In general telecom equipment use unregulated 48V power supply (typically 36 to 75V) or 24V (18 to 36V). Typical power levels are 50-100W per card. In telecom applications it is common to use "brick" modules to generate 3.3V or 5V for distribution within the card. Local regulators then produce lover voltages as needed (for example 2.5V is becoming popular). High power telecom cards can use a 12V intermediate bus. Manufacturers have also discussed on 7V or 8V intermediate-bus voltages.
The mains voltage is alternating voltage which can vary from country to country somewhat. For example USA uses 110-120V AC power (plus minus some tolerance) at 60 Hz frequency. Europe uses 230V AC +/- 10% at 50 Hz frequency. One must design the power supply so that the nominal device will accept a wider band. Then one must control the manufacturing spreads so that the limits of no device enter the band, or one must weed out bad ones in testing forrejection or rework, or one must have plans for dealing with the after-effects of non-compliant devices entering the marketplace.
The mains power supplies in practically all equipment are very well insulated from the casing (there are very few exception to this). In Europe all mainspowered equipment has to comply with the Low Voltage Directive which has minimum mains to casing insulation resistances. USA has it's own regulations on this insulation.
For example VCRs are low voltage machines and their circuits are supplied via a linearpower supply with a big mains transformer or a switched mode power supply that isolates from the mains. The metal case is floating.For example a typical PC is a low voltage machine which is supplied with a switched mode power supply that isolates the output from the mains input.
The PC metal case is connected to themains ground with a ground connector on the mains cable and ground connector on the mains input connector. In PC the output 0V is connected to the PC ground (thus to mains ground).
No isolation is perfect. The isolation must be good enough to be safe (high enough reistance and withstands enough voltage rating). The demans vary somewhat from country to country and equipment type to another. Testing the quality of mains isolation is a necessary test for making sure that the equipment operating safely (mains does not leak too much to the case). One way to test the isolation quality is to use an insulation tester, which supplies few hundred volts to the main input and measures the resistance to the case at that voltage. Many equipment manufacturers make usualy also a hi-volt testing (test voltage usually in 1.5-2 kV range AC or DC voltage).
One way to check that the insulation in equipment is OK is to perform a "leakage test". Usea 1.5 K, 10 watt resistor with a .15 mfd 150 volt cap in parallel with theresistor. Take an AC voltmeter with at least 5000 ohms-per-volt sensitivity& measure the voltage drop across the resistorcap network. With one end ofthe network at earth ground and the other end attached to all exposed metalparts the voltage shouldn't exceed .3 volts RMS. This is the industry standard test in the U.S.
Power supplies typically have a high inrush current when they are connected to mains power. This inrush current can be seen on both traditional transformer based power supplies and switch mode power supplies. In ac/dc power converters above a few watts, a large inrush current flows when the input capacitors are suddenly charged during the initial application of power. In traditional linear power supplies the initial surge is caused by both the magnetization of the transformer core (usually takes one mains half cycle) and then the main capacitor charging time (time depends on cpacitor size and transformer current output capability). The initial surge can be very high on some toroidal transformer. In switch mode power supplies the initial power surge (that can be a very large on some cases) is caused by the mains voltage power storage capacitors getting charged quicly. Universal switch mode power supplies are particularly subject to high inrush current since their input capacitors must be large enough to handle line voltages as low as 110 Vac, as well as voltages as high as 240 Vac at turn-on. Designers of commercial, industrial, and medical systems need to pay special attention to inrush current. High inrush current can damage power supply sooner or later and can also cause circuit breaker to trip.
It quite possible to get an inrush-current spike of 50 A or more on a nominal 120-Vac line (170 V peak). In countries where the nominal line voltage is 240 Vac, the inrush current can exceed 100 A. This large inrush current degrades the performance and lifetime of the power supply in a number of ways: sparking of the switch contacts, thermally overstress the input rectifiers, stressing the capacitors, slowly degrade the fuse, etc..
Power-supply manufacturers use one of several inrush-current-limiting techniques to avoid these problems:
Higher inrush-current specifications equate to greater stress on the rectifier and lower reliability.
Measuring power supplies
Wiring power supplies to load
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