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What is a Power Supply?

In general, a source of power is a source of energy, this energy can be of various types, thermal, nuclear, electric, etc. In the middle of electronics, most people call power source to an electrical circuit which converts the electricity from AC voltage (Vac Vac or English) to a DC voltage (Vdc Vdc or English).

The AC voltage or Vac is, for example, we get from the outlet of our homes, the voltage and current is alternating as its polarity varies with a specific frequency. For example, Mexico nominal voltage is 110 volts at 60 Hz. The same used in USA, but different than it has for example in Argentina, Japan and Europe.

The direct voltage has a fixed frequency unchanged polarity. This voltage is used by the vast majority of electronic circuits, example of this voltage is found in alkaline batteries or rechargeable type found for example in the mobile phone.

Most electronic circuits used direct voltage, but always have a type of power source that converts Vac to Vdc, the source can be external or internal. A battery charger is considered a source of power, which transforms the Vac to Vdc to charge the rechargeable battery.

The illustration shows a typical charger that converts input Vac
to Vdc which has an input is shown
110-240 volt s AC with frequency
of 50-60 Hz and demand 0.2A at the entrance. The output is a voltage
CD of 5 volts with 0.8 to 1 ampere output. The maximum output power
is 5 watts.

The AC voltage is used to transmit electricity from one point to another, the more distant it is a point on the other, the greater the energy loss by transmission to minimize this loss, the voltage is increased to several thousand volts with small streams using transformers rise. Down transformers are used when electricity is approaching its final destination.

Power supplies can be very simple or very complex, the simplest type is the black box we put into the socket to charge your mobile phone. The specifications of these sources are the output voltage specified in volts and current capacity, specified in amperes or power, which is the result of multiplying the voltage and the maximum current available. Power is expressed in watts.

Computers bench power supplies use high efficiency providing several fixed voltages via standard connectors, these sources provide fixed voltages of +5, +12 and -12 volts through several identical connectors that connect to the main board, hard drives and other computer components.

People who design postcards, engineering students and researchers often use power sources to power their circuits or experiments. These sources are usually variable output, you can vary the level of voltage and current manually with separate knobs. Such sources typically has voltage and current indicators. The voltage is varied so that the circuits operate correctly, the current that is supplied is limited to prevent damage to the components during the assembly under test this evil assembly or designed.

The figure shows a DC power supply with variable output. The digital display shows isolate from electrical supply voltage or output. You can work in CC mode (constant current) or CV (constant voltage), an LED indicates the mode in which it operates. There knobs dedicated to adjusting fine or coarse voltage or current voltage. Three terminals have. One for the positive voltage (red) One for the negative (black) and earth ground (Green).

CC mode or constant current can be used in chemical processes that require the passage of a current for a period of time to create a reaction.

The electronic designer may have analog and digital electronics in your circuit, and this designer requires a source that can provide more than one voltage source simultaneously. A source for powering digital logic circuits, and two other sources that feed the analog circuitry with two voltages of opposite polarity. A common source of power in an electronics laboratory has a set of three outputs, about 5V and two other variables with ranges of 0-30 volts.

Typical Lab Power Supply. They are used in schools and research centers power electronic circuits under test.
This model provides 3 independent outputs with ranges of 0-30 and
0-3 volts amperes and a fixed output of
5 volts with a current of 0-3 A. These sources
are very flexible because the variable outputs can be configured
in serial mode or parallel to obtain twice the voltage or current output.

The outputs of power supply are usually floated. This reference to the negative voltage circuit, which might be different from the physical land of the electrical installation. Another reason that the outputs of the sources are floated is to reverse the polarity, or to connect them serially or in parallel to double the capacity of voltage in the first case or the current capacity in the second case.

The sources laboratory for testing prototypes are low power, with a range of 80-300 watts, with one to four individual outputs for added flexibility.

For applications that require more power and broader voltage and current ranges have high power sources, there are output from 600W up to several tens of kilowatts. Applications for these sources can be found in itself is manufactured, which is required to feed multiple circuits simultaneously, or simulate high current batteries like those found in cars or airplanes. Sometimes these high power sources are used for chemical process like chrome or ionization.

The sources of high power and high efficiency for the use of processes from manufacture is designed to be rack-mounted, as they are part of an instrument panel. This source has control of voltage and current type of lock that prevents the parameters are moved by someone outside the process or by mistake. This source has up to 3 KW or KVA output.

The control of sources can be done manually by varying the voltage and current knobs. But in a plant from manufacture, for example, requires that a controller or computer to communicate with the power to control it remotely. There are several ways to remotely control a source of power, including remote control options can mention RS232, GPIB, USB and Ethernet LAN port. There are some similar methods that control the output using a signal proportional to the desired voltage output analog control and a signal for switching on or off of the exit.

An application where the remote control is used using a computer is in a factory breakers where they check each of the breakers applying the necessary current to cause the breaker it acts off the power, an automatic system can increase the current to some extent and sensing that current the breaker acts, a signal controller can send the breaker a lot of good breakers or separate it defective.

Above the rear of the power source in the above mentioned figure shows. From left to right and top to bottom we can see first terminals of the output DC (direct current). In the sources of high output power is requires a professional electrical installation where three phases indicated here as L1 / F1 are used, L2 / F2 and L3 / F3, each phase with its own fuse. Bottom right is the D type connector for remote control, useful for controlling the source with a PLC. The two cables whites who go to a J11 connector on the bottom. This is the connection sensing that helps to compensate for the voltage drop in output cables, by default connect directly departure, but can be connected to the load to compensate voltage drops.

Power supplies laboratory usually also have terminals sensing , in English called sense , a positive terminal and a negative , these terminals are used to compensate for voltage drop that occurs in the cables from the power supply to the assembly under test.

There are also sources of AC power, the input of these sources is also AC voltage The difference is that a laboratory source AC can vary its output voltage very accurately, vary its frequency, and in some cases even vary the harmonic content to stress font designs that transform VAC to VCD or test voltage -operated machines alternate, as AC motors, which use one or more stages.

Classification of Power Supplies.

Figure 1: Power Supply

Also known as Power Supply can be defined as circuits that transform the input power , and either AC or DC ; in output AC or DC .

This definition excludes Energy source based on the principle of a rotating machine and distinguishes the Power Supply most of the Energy sources that get their power from other forms of energy.

There are four general classifications for Power Supply:

1. Input AC - AC Output: Line Regulators and frequency changers

2. Input DC - DC Output: DC Converters & Regulators

3. Input DC - Output AC: Inverters

4. AC Input - Output DC

The last category is the most common of all and which is usually referred to as Power Supply.

There are also four modes of operation that the power supply may provide DC output:

Constant output voltage: The output voltage remains constant despite changes in load, temperature or line. A DC power source would ideally zero output impedance at all frequencies. For a constant output without curling effect a control element or control technology is required Regulatory technical best known are :

a) Linear Regulation

b) Pre series regulation or regulation

c) Switched

d) Through SCR

Constant current output: The output current remains constant despite changes in load , output, or temperature. The power source that provides constant current should have an infinite impedance at full output frequency. This type of power supplies constant current has many applications in circuit design and semiconductor test.

Limit voltage

Current limit

The power source may be programmable by means of a computer with USB communication ports, Ethernet (LXI ) , GPIB or RS232. These interfaces are used in automated test and measurement systems.

Some power supplies can be programmed from the front panel with a specific routine work, such as SGI series of Sorensen.

The power output of a source is obtained by multiplying the maximum voltage and current capacity. Thus, a source that generates an output voltage of 300 volts DC at 10 amperes have a capacity of (300 x 10 ) 3000 Watts or 3 KW ( Kilo - Watts ).

Consideraciones y Especificaciones a Considerar en Fuentes de Poder.

Noise and Ripple Output

It refers to RMS or peak to peak voltage variation that has the output power source.

Transient Response

It is the supply capacity to meet current demands great variation in short periods of time

Speed up or down (slew-rate)

Is the speed with which the power source is turned on, off or varies the voltage or output current from an instruction for a communication port or via manual controls.

Load Regulation

Sets Supply Ability to maintain a constant voltage when the load varies.

Line Regulation

The AC power line may vary from one country to another, or simply a place to another, the power supplies must be able to regulate their output even when the AC input voltage has a variation within specification working source.


Stability is specified as the ability to maintain the output voltage and current over a long period of time.


The percentage of conversion efficiency of the input power from the power source output.

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