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Electrical power supplies

This term covers the power distribution system together with any other primary or 

secondary sources of energy such as:

• Conversion of one form of electrical power to another desired form and voltage.This typically involves converting 120 or 240 volt AC supplied by a utility

company (see electricity generation) to a well-regulated lower voltage DC for 

electronic devices. Low voltage, low power DC power supply units are commonlyintegrated with the devices they supply, such as computers and household

electronics. For other examples, see switched-mode power supply, linear 

regulator , rectifier  and inverter (electrical).

• Batteries

• Chemical fuel cells and other forms of energy storage systems

• Solar power 

• Generators or alternators (particularly useful in vehicles of all shapes and sizes,

where the engine has torque to spare, or in semi-portable units containing aninternal combustion engine and a generator) (For large-scale power supplies, see

electricity generation.)

Constraints that commonly affect power supplies are the amount of power they can

supply, how long they can supply it without needing some kind of refueling or 

recharging, how stable their output voltage or current is under varying load conditions,

and whether they provide continuous power or pulses.

The regulation of power supplies is done by incorporating circuitry to tightly control the

output voltage and/or current of the power supply to a specific value. The specific value

is closely maintained despite variations in the load presented to the power supply'soutput, or any reasonable voltage variation at the power supply's input. This kind of 

regulation is commonly categorized as a Stabilized power supply.

[edit] Power supply types

Power supplies for electronic devices can be broadly divided into linear and switching power supplies. The linear supply is a relatively simple design that becomes increasingly

 bulky and heavy for high current devices; voltage regulation in a linear supply can result

in low efficiency. A switched-mode supply of the same rating as a linear supply will be

smaller, is usually more efficient, but will be more complex.

[edit] Battery power supply [1]

A battery is a type of linear power supply that offers benefits that traditional line-operated power supplies lack: mobility, portability, and reliability. A battery consists of multiple

electrochemical cells connected to provide the voltage desired.

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The most commonly used dry-cell battery is the carbon-zinc dry cell battery.[2] Dry-cell

 batteries are made by stacking a carbon plate, a layer of electrolyte paste, and a zinc plate

alternately until the desired total voltage is achieved. The most common dry-cell batterieshave one of the following voltages: 1.5, 3, 6, 9, 22.5, 45, and 90. During the discharge of 

a carbon-zinc battery, the zinc metal is converted to a zinc salt in the electrolyte, and

magnesium dioxide is reduced at the carbon electrode. These actions establish a voltageof approximately 1.5 V.

The lead-acid storage battery may be used. This battery is rechargeable; it consists of lead

and lead/dioxide electrodes which are immersed in sulfuric acid. When fully charged, this

type of battery has a 2.06-2.14 V potential. During discharge, the lead is converted tolead sulfate and the sulfuric acid is converted to water. When the battery is charging, the

lead sulfate is converted back to lead and lead dioxide.

A nickel-cadmium battery has become more popular in recent years. [3]This battery cell is

completely sealed and rechargeable. The electrolyte is not involved in the electrode

reaction, making the voltage constant over the span of the batteries long service life.During the charging process, nickel oxide is oxidized to its higher oxidation state and

cadmium oxide is reduced. The nickel-cadmium batteries have many benefits. They can be stored both charged and uncharged. They have a long service life, high current

availabilities, constant voltage, and the ability to be recharged.

[edit] Linear power supply

A home-made linear power supply (used here to power  amateur radio equipment)

An AC  powered linear power supply usually uses a transformer to convert the voltage

from the wall outlet (mains) to a different, usually a lower voltage. If it is used to produce

DC, a rectifier is used. A capacitor is used to smooth the pulsating current from the

rectifier. Some small periodic deviations from smooth direct current will remain, which isknown as ripple. These pulsations occur at a frequency related to the AC power 

frequency (for example, a multiple of 50 or 60 Hz).

The voltage produced by an unregulated power supply will vary depending on the loadand on variations in the AC supply voltage. For critical electronics applications a linear 

regulator  will be used to stabilize and adjust the voltage. This regulator will also greatly

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reduce the ripple and noise in the output direct current. Linear regulators often provide

current limiting, protecting the power supply and attached circuit from overcurrent.

Adjustable linear power supplies are common laboratory and service shop test equipment,allowing the output voltage to be set over a wide range. For example, a bench power 

supply used by circuit designers may be adjustable up to 30 volts and up to 5 amperesoutput. Some can be driven by an external signal, for example, for applications requiring

a pulsed output.

The simplest DC power supply circuit consists of a single diode and resistor  in series

with the AC supply. This circuit is common in rechargeable flashlights.

[edit] AC/ DC supply

Main article: AC/DC (electricity)

In the past, mains electricity was supplied as DC in some regions, AC in others. Asimple, cheap linear power supply would run directly from either AC or DC mains, often

without using a transformer. The power supply consisted of a rectifier and a capacitor 

filter. The rectifier was essentially a conductor, having no sudden effect when operating

from DC.

[edit] Switched-mode power supply

Main article: Switched-mode power supply

A computer 's switched mode power supply unit.

A switched-mode power supply (SMPS) works on a different principle. AC mains input

is directly rectified without the use of a transformer, to obtain a DC voltage. This voltageis then sliced into small pieces by a high-speed electronic switch. The size of these slices

grows larger as power output requirements increase.

The input power slicing occurs at a very high speed (typically 10 kHz — 1 MHz). High

frequency and high voltages in this first stage permit much smaller  step downtransformers than are in a linear power supply. After the transformer secondary, the AC is

again rectified to DC. To keep output voltage constant, the power supply needs a

sophisticated feedback controller to monitor current draw by the load.

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Modern switched-mode power supplies often include additional safety features such as

the crowbar circuit to help protect the device and the user from harm.[4] In the event that

an abnormal high current power draw is detected, the switched-mode supply can assumethis is a direct short and will shut itself down before damage is done. For decades PC

computer power supplies have also provided a  power good signal to the motherboard

which prevents operation when abnormal supply voltages are present.

Switched mode power supplies have an absolute limit on their minimum current output.[5] They are only able to output above a certain wattage and cannot function below that

 point. In a no-load condition the frequency of the power slicing circuit increases to great

speed, causing the isolation transformer to act as a tesla coil, causing damage due to theresulting very high voltage power spikes. Switched-mode supplies with protection

circuits may briefly turn on but then shut down when no load has been detected. A very

small low-wattage dummy load such as a ceramic power resistor or 10 watt light bulb can be attached to the supply to allow it to run with no primary load attached.

Power factor has become a recent issue of concern for computer manufacturers. Switchedmode power supplies have traditionally been a source of   power line harmonics and have a

very poor power factor. Many computer power supplies built in the last few years nowinclude power factor correction built right into the switched-mode supply, and may

advertise the fact that they offer 1.0 power factor .

By slicing up the sinusoidal AC wave into very small discrete pieces, the portion of the

alternating current not used stays in the power line as very small spikes of power thatcannot be utilized by AC motors and results in waste heating of power line transformers.

Hundreds of switched mode power supplies in a building can result in poor power quality

for other customers surrounding that building, and high electric bills for the company if 

they are billed according to their power factor in addition to the kilowatts used. Filteringcapacitor banks may be needed on the building power mains to suppress and absorb these

negative power factor effects.

[edit] Programmable power supply

Programmable power supplies are those in which the output voltage can be varied

remotely. One possible option is digital control by a computer interface. Variable properties include voltage, current, and frequency. This type of supply is composed of a

 processor, voltage/current programming circuits, current shunt, and voltage/current read-

 back circuits.

Programmable power supplies can furnish DC, AC, or both types of output. The AC

output can be either single-phase or three-phase. Single-phase is generally used for low-

voltage, while three-phase is more common for high-voltage power supplies.

When choosing a programmable power supply, several specifications should beconsidered. For AC supplies, output voltage, voltage accuracy, output frequency, and

output current are important attributes. For DC supplies, output voltage, voltage

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accuracy, current, and power are important characteristics. Many special features are also

available, including computer interface, overcurrent protection, overvoltage protection,

short circuit protection, and temperature compensation. Programmable power suppliesalso come in a variety of forms. Some of those are modular, board-mounted, wall-

mounted, floor-mounted or bench top.

Programmable power supplies are now used in many applications. Some examples

include automated equipment testing, crystal growth monitoring, and differential thermalanalysis [6].

[edit] Uninterruptible power supply

Main article: Uninterruptible power supply

An Uninterruptible Power Supply (UPS) takes its power from two or more sources

simultaneously. It is usually powered directly from the AC mains, while simultaneously

charging a storage battery. Should there be a dropout or failure of the mains, the batteryinstantly takes over so that the load never experiences an interruption. Such a scheme can

supply power as long as the battery charge suffices, e.g., in a computer installation,

giving the operator sufficient time to effect an orderly system shutdown without loss of data. Other UPS schemes may use an internal combustion engine or turbine to

continuously supply power to a system in parallel with power coming from the AC

mains. The engine-driven generators would normally be idling, but could come to full power in a matter of a few seconds in order to keep vital equipment running without

interruption. Such a scheme might be found in hospitals or telephone central offices.

[edit] High-voltage power supply

High voltage refers to an output on the order of hundreds or thousands of volts. High-

voltage power supplies use a linear setup to produce an output voltage in this range.

When choosing a high-voltage power supply, there are several options to consider. Some

of these are maximum current, maximum power, maximum voltage, output polarity, user interface, and style. The first four of these characteristics of course depend upon the

supply's intended application. There are many available types of user interfaces. For 

example, the interface may be local in the form of a digital meter, or analog meter. Also,the interface can be remote, as in a computer connection. Numerous styles of high-

voltage power supplies are also manufactured. Available models come in printed circuit

 board mount, open frame (as designed to be incorporated into an instrument), and rack mount. Models with multiple outputs can also be found [7].

[edit] Voltage multipliers

Voltage multipliers, as the name implies, are circuits designed to multiply the input

voltage. The input voltage may be doubled (voltage doubler), tripled (voltage tripler),

quadrupled (voltage quadrupler), etc. Voltage multipliers are also power converters. An

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AC input is converted to a higher DC output. These circuits allow high voltages to be

obtained using a much lower voltage AC source.

Typically, voltage multipliers are composed of half-wave rectifiers, capacitors, anddiodes. For example, a voltage tripler consists of three half-wave rectifiers, three

capacitors, and three diodes. Full-wave rectifiers may be used in a different configurationto achieve even higher voltages. Also, both parallel and series configurations are

available. For parallel multipliers, a higher voltage rating is required at each consecutivemultiplication stage, but less capacitance is required. The voltage capability of the

capacitor limits the maximum output voltage.

Voltage multipliers have many applications. For example, voltage multipliers can be

found in everyday items like televisions and photocopiers. Even more applications can befound in the laboratory, such as cathode ray tubes, oscilloscopes, and photomultiplier 

tubes.[8][9]

[edit] Power supply applications

[edit] Computer power supply

Main article: Computer power supply

A modern computer power supply is a switched-mode supply designed to convert 110-

240 V AC power from the mains supply, to several output both positive (and historically

negative) DC voltages in the range 12V to 3.3V. The first computer power supplies were

linear devices, but as cost became a driving factor, and weight became important,switched mode supplies are almost universal.

The diverse collection of output voltages also have widely varying current draw

requirements, which are difficult to all be supplied from the same switched-mode source.

Consequently most modern computer power supplies actually consist of several differentswitched mode supplies, each producing just one voltage component and each able to

vary its output based on component power requirements, and all are linked together to

shut down as a group in the event of a fault condition.

The most common modern computer power supplies are built to conform to the ATX 

form factor . The power rating of a PC power supply is not officially certified and is self-

claimed by each manufacturer.[10]A common way to reach the power figure for PC PSUs

is by adding the power available on each rail, which will not give a true power figure.The more reputable makers advertise "True Wattage Rated" to give consumers the idea

that they can trust the power advertised.

[edit] Welding power supply

Main article: Welding power supply

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Arc welding uses electricity to melt the surfaces of the metals in order to join them

together through coalescence. The electricity is provided by a welding power supply, and

can either be AC or DC. Arc welding typically requires high currents typically between100 and 350 amps. Some types of welding can use as few as 10 amps, while some

applications of spot welding employ currents as high as 60000 amps for an extremely

short time. Older welding power supplies consisted of transformers or engines drivinggenerators, while modern ones implement semiconductors and even microprocessors,

greatly reducing their size and weight.

[edit] AC adapter

Switched mode mobile phone charger See also: Wall wart

A linear or switched-mode power supply (or in some cases just a transformer) that is built

into the top of a plug is known as a "wall wart", "power brick", "plug pack", "plug-in

adapter", "adapter block", "domestic mains adapter" or just "power adapter". They areeven more diverse than their names; often with either the same kind of  DC plug offering

different voltage or polarity, or a different plug offering the same voltage. "Universal"

adapters attempt to replace missing or damaged ones, using multiple plugs and selectorsfor different voltages and polarities. Replacement power supplies must match the voltage

of, and supply at least as much current as, the original power supply.

The least expensive AC units consist solely of a small transformer , while DC adapters

include a few additional diodes. Whether or not a load is connected to the power adapter,the transformer has a magnetic field continuously present and normally cannot be

completely turned off unless unplugged.

Because they consume standby power , they are sometimes known as "electricity

vampires" and may be plugged into a power strip to allow turning them off. Expensiveswitched-mode power supplies can cut off leaky electrolyte-capacitors, use powerless

MOSFETs, and reduce their working frequency to get a gulp of energy once in a while to

 power, for example, a clock, which would otherwise need a battery.

This type of power supply is popular among manufacturers of low cost electrical items

 because:

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1. Devices sold in the global marketplace don't need to be individually configured

for 120 volt or 230 volt operation, just sold with the appropriate AC adapter.

2. The device itself doesn't need to be tested for compliance with electrical safetyregulations. Only the adapter needs to be tested.

3. Product development becomes faster and cheaper, because the heat produced by

the power supply is outside of the product.4. The device itself can be smaller and lighter, since it does not contain the power 

supply.

[edit] Polarity

Diagram showing positive tip polarity on the left and negative tip polarity on the right. Toread diagram: The center positive drawing on the left indicates that the center (tip) of the

output plug is positive (+) and the barrel of the output plug is negative (-). Some multi-adaptors use "tip" to indicate the center, but include no explanation that tip is used tomean center.

AC-to-DC adapters have polarity; even if the plug fits into a device, the positive and

negative connections may be oriented the wrong way. It is necessary to use an adapter 

with the correct polarity to avoid damage. Standardized  polarity symbols are usually usedto label polarity.

[edit] Overload Protection[11]

Power supplies should have some type of overload protection. Overload protection is

important to protect the electronic equipment hooked up to the power supply and to also prevent overheating, which could potentially lead to an electrical fire. Fuses and circuit

 breakers are two of the more frequent mechanisms used for overload protection.

[edit] Fuses

A piece of wire is connected between two metal ends. The two metal ends of the fuse are

connected by either a tube of glass or plastic which surrounds the wire. If too muchcurrent flows, the wire overheats and melts. This interrupts the power supply, and the

equipment stops working until the problem that caused the overload is identified and the

fuse is replaced.

There are two types of fuses, slow-blow and fast-blow. In a fast-blow fuse, the wireinside the fuse will melt if the current exceeds the rated current, even if it is just for a

fraction of second. This concise process is important in electronic equipment where even

a small spike in the current could damage the equipment. A slow-blow fuse is designed to

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only melt when there is a continuous overload. Slow-blow fuses are ideal for motor 

systems.

[edit] Circuit Breakers

One benefit of using a circuit breaker as opposed to a fuse is that it can simply be resetinstead of having to constantly replace the blown fuse. A circuit breaker works once anoverloaded current causes some element to heat and trigger a spring which shuts the

circuit down. Once the element cools, and the problem is identified the breaker can be

reset and the power restored.

[edit] Power conversion

The term "power supply" is sometimes restricted to those devices that convert some

other form of energy into electricity (such as solar power and fuel cells and generators).

A more accurate term for devices that convert one form of electric power into another 

form (such as transformers and linear regulators) is  power converter . The most commonconversion is AC-DC. This is a conversion from the household current AC, to the direct

current that is used in your car, and most electronics.

A dc power supply circuit connects a plurality of dc circuit breakers to a semi-conductor converter, returning again to the semi-conductor converter through a dc driving part such

as an electric railcar connected to each dc circuit breaker. A second dc circuit breaker of 

larger capacity than the above-mentioned dc circuit breakers is provided in a returncircuit and opened when a short circuit current is detected. A current decreasing means

opens the second dc circuit breaker to decrease the short circuit current and includes, for 

example, a series-circuit of a resistor R and a reactor L. The dc power supply circuit has a

large interruption capacity with low resistance loss.

This universal power supply contains, beside the bridge rectifier, a voltage stabilizer (78xx) and a pnp power transistor. This combination allow a load current up to 5 A. As

you know a voltage stabilizer in a TO-220 package can deliver up to 1A. The additional

 power transistor takes the load current of about 200mA.The transformer voltage must be greater with 4V than DC stabilized voltage. C1 is

calculated for 1A/1000uF, so at 5A C1 must have 4700uF. Both, transistor and voltage

stabilizer must be mounted on a heatsink.

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Specifications:

• Input Voltage : 220V AC +/- 10%.

• Line & Load Regulation : +/- 0.05%.

• Ripple and Noise : Less than 5mV.

• Protection : Against short Circuit and Overload.

• Transient Recovery : 100 micro seconds.

• Indicating Meters:

For Variable Output Power Supplies:

- 1 set of 3 ½ digits Digital Voltmeter and Ammeter to measure outputs.

For Dual Tracking Output Power Supplies:

- 1 set of 3 ½ digits Digital Voltmeter and Ammeter to measure outputs. A switch is

provided to select these meters for any output.

For Dual Variable Output Power Supplies:

- 2 sets of 3 ½ digits Digital Voltmeter and Ammeter to measure both outputs.

For Multi Output Power Supplies:

- 1 set of 3 ½ digits Digital Voltmeter and Ammeter to measure outputs. A switch set is

provided to select these digital meters for any output Voltage.

• Special Features:

RFI Noise filter at AC Input.

AC line status Indicator.

2 Years Warranty. 

Models:

Fixed Output Power Supplies:

1. A0502 : 5V +/-10%, 2A

2. A0505 : 5V +/-10%, 5A

3. A0510 : 5V +/-10%, 10A

Variable Output Power Supplies: (Constant Voltage /

Current Limit)

1. C3002 : 0 - 30V, 2A2. C3005 : 0 - 30V, 5A3. C3010 : 0 - 30V, 10A

4. C6001 : 0 - 60V, 1A

5. C6002 : 0 - 60V, 2A

Dual Tracking Output Power Supplies:

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Without Panel Meters:

1. B1201 : +/-3V to +/-18V, 1A

2. B1202 : +/-3V to +/- 18V, 2A

With Panel Meters:

1. B1201M : +/-3V to +/-18V, 1A2. B1202M : +/-3V to +/- 18V, 2A

Dual Variable Output Power Supplies: (Constant

Voltage / Current Limit)

(Output Voltage : 2 x ( 0 - 30V )

1. D3001 : 2 X (0-30 V, 1A)

2. D3002 : 2 X (0-30 V, 2A)

Multi Output Power Supply:

1. M1004 : 0-30V/2A, 5V/2A, +/- 3V to +/- 18V/ 1A.

2. M0403 : 5V/2A, +/-3V to +/- 18V/1A.