Power supply

A power supply (English Power Supply Unit, PSU ) is a stand-alone unit or a module for supplying power to devices or modules that require different voltages and currents, as is provided from the mains. Output voltage and maximum output current may be fixed or variable.

  • 2.2.1 fixed voltage power supplies
  • 2.2.2 Laboratory Power Supplies

Species

Power supplies are divided into switching power supplies and transformer power supplies, the latter still in regulated and unregulated. They all are available in different versions depending on the application.

But not limited to - - Today, for the most part are switching power supplies are used. They operate at higher frequencies than the mains frequency - typical values ​​are in the range of a few 10 kHz to a few 100 kHz. This allows for the same power using smaller and lighter transformers and higher efficiency. Virtually all switching power supplies provide a regulated DC voltage or a regulated DC. There are special power supplies, which you may only be operated under load, as it displays open ports such a high voltage would build up that it would self-destruct. They vary depending on the type, either the switching frequency or the pulse-width ratio, whereby energy loss can be avoided. Although they require a higher component costs as Power supplies, they are now due to the increase in raw material costs and energy prices are more than competitive.

Power supplies have, compared to the switching power supplies on a simpler structure, as shown in the illustration: They contain a transformer ( 1) whose primary winding is fed directly to the AC mains supply voltage and frequency. It converts the voltage on the or the required output values ​​and provides DC isolation safely. For power supplies without galvanic isolation auto transformers can be used. The secondary alternating voltage of the transformer is converted into a DC voltage by the rectifier (2) and the smoothing capacitor (3). The following linear regulator (4) and buffer capacitor (5 ) represent the constant output voltage sure which necessarily heat losses occur. Because unregulated power supplies lack the linear regulators, they do not provide constant output voltage. But they are components with lower cost, high efficiency and low cost. Sometimes non-regulated Power supplies consist only of the power transformer; they then give off alternating voltage.

Power supplies constant current in the form of a constant current source are rare. You will be required, for example for the operation of semiconductor lasers or with the charger for charging rechargeable batteries. Furthermore, universal laboratory power supplies are used in this mode.

Designs

Power Supplies are offered depending on the application and deploy, output in different forms:

External Plug In Adaptors

Plug power supplies are power supplies, which form a unit with the mains plug. They are used for small services that are below 10 W in conventional construction and 50 W with switching power supplies. The plug for connection to the AC network is integrated into the housing of the power supply. The output low voltage is usually done via a cable to be supplied to the device. But there are also types that have on the low voltage side of the socket, such as USB chargers.

Switching power supply

Meanwhile, all AC adapters are designed as switching power supplies, because the legally required efficiency standards can only be realized with such a low cost. Switching power supplies are not only much lighter and smaller than transformer power supplies, but also have a lower idle power and higher efficiency in operation. In addition, the output voltage is more stable than that of unstabilized conventional power adapters. They are short -circuit proof and can be operated in all standard voltages and the world through a wide-range input in the range of 85 V to 250 V. However, by occurring in its interior high switching frequencies they generate more noise in the power grid, making noise suppression necessary.

The idle power dissipation is limited by law of the EU on 1 watt.

Transformer power supply

Previously simple designs of transformer, rectifier and filter capacitor came in many power supply units used, whose electrical efficiency is significantly lower at full load below 50%. They are found today only in special cases. "Stabilized" with the exception of devices marked is no need for a voltage regulator. Different output voltages can be achieved by switching winding taps of the transformer. The open-circuit voltages unstabilized devices are often much higher than the rated voltage. The transformers contain a resettable or non-resettable thermal fuse; The latter are unusable after overload. Plug power supplies with AC output only contain a transformer.

Power supplies are often designed for low weight and low cost: they use the iron core of a maximum, which is often of inferior quality. Thus several watts of electricity from the grid even without a load or without current drain. The above circumstance drew plug power supplies in the criticism of environmentalists. 1998 calculated the BUND ago in a media campaign that by consistently switching off or pulling all power supplies (not only External Plug In Adaptors ) not in-service electrical equipment in German-speaking could save an average nuclear power plant.

Plug

When connected to that of the appliance a variety of connectors and voltages used. Frequently leads the inner contact positive polarity, the outer mass. On many devices, hollow plugs and jacks are to be found, whereby the former are preferable to the plugs. Jack cause when inserting a temporary short circuit and should always be plugged or dissolved only in a de-energized power supply. And " -: -" In most cases the polarity by two concentric circles with " " sign is marked on the AC adapter.

The picture shows a selection of connectors (from left to right):

  • Hollow plug EIAJ -01 ( yellow cap ) 2.35 mm × 0.7 mm ( outer diameter x inner diameter )
  • 2,5 mm
  • DC Plug 3.5 x 1.35 mm
  • 3,5 mm
  • Hollow plug EIAJ -02 ( yellow cap ) 4 × 1.7 mm
  • DC Plug 5.0 x 2.1mm

Barrel connector size 5.5 × 2.1 mm and 5.5 × 2.5 mm are also to be found. Most of them are equipped with jacks for 5.0 × 2.1 mm compatible.

With mobile power supplies is now available for the device class of smartphones USB connector standardized throughout Europe ( EN 62684:2010 ).

A USB 2.0 connector has four wires plus a shield. The stabilized voltage of 5 V is fed to the outer pins 1 and 4. Outputs of the standard USB 2.0 provide a maximum of 500 mA from USB 3.0 up to 900 mA. "Recognize" the phones USB charger to the resistance between the data lines D and D-, which is less than 200 ohms or shorted. Without this connection devices would assume that there is a computer in sleep mode, and should refer to a maximum of 0.5 mA current. In practice, this standard is rarely adhered to and there are added 500 mA.

Charging cable from Apple encode the performance of a network device via a voltage. To the data lines D and D- is present Are the data lines not connected, devices can be used by this manufacturer, although the AC adapter, but charging the device battery does not work. This coding is not standardized and could at any time be changed by Apple. Following voltages to the data lines associated with the respective charge currents:

The voltages of 2 V and 2.75 V are typically produced by a voltage divider at the 5- V supply line, for example, by the pair of resistors 75 ohms and 49.9 ohms or 43.2 ohms and 49.9 ohms.

Characteristics

The following product designations are used:

  • Polarity: DC power supplies have a positive or negative polarity, which is marked with the shown in the adjacent figure symbols and corresponds to the polarity of the inner pole plug and socket. The polarity of the power supply must match the order of the powered device match to prevent damage (usually destruction of the entire device).
  • " Stabilized " means that the output voltage maintains its nominal value even at idle. ( Only found on transformer power supplies. )
  • Output: xx volts ⎓ means rectified, filtered power; contains AC components at idle the output voltage rises partly to significantly above the rated voltage.
  • Output: xx volts AC or ~ means AC voltage output (eg for light chains ).

The voltage specification follows the specification of the maximum extractable current or the output power.

Furthermore, symbols or pictograms are to be found:

  • Crossed out wheeled bin: according to electronic waste regulation are not worn-out equipment for residual waste
  • Double Square: protective isolation voltage- carrying parts
  • Stylized house: use indoors only
  • CE marking: A free trade indicators for the European Union. By affixing the CE marking confirms the distributor that the product complies with the applicable European product-specific EU directives.
  • By a stroke separate overlapping circles: protective separation between power and output voltage ( SELV )

Stand-alone devices

Fixed voltage power supplies

For medium power ( 10-200 W ), there is a wide range of power supplies with common output voltages (one or more AC or DC voltages) in the form of external units that are powered via a partially on the device plug-in power cable and the consumer of an outgoing line supply with connector.

The use of external power supplies as opposed to integrated into the device power supplies, device manufacturers some important advantages:

Also this design ( such as printers or laptops ) has only rarely on a power switch, so that it is possible through the use of switchable power strips save some energy. In particular, inkjet lead but after a complete power disconnection often a complex self-test, in which much ink unnecessarily.

Laboratory Power Supplies

→ Main article: DC power supply

So-called laboratory power supplies, also known as laboratory power supplies are varied usable devices. They usually have a continuously adjustable voltage limiting and also adjustable current limit, further includes a current and voltage display.

Built-in power supply

For higher ratings (over 100 W) are often designed as a module or built-in appliance power supplies within appliances or cabinets. The requirements for personnel protection are then lower. The integration of the power supply increases the other hand, however, the security requirements of the overall device, as this now has to meet the requirements eg touch protection, Kriechspannungsabständen and overvoltage protection or protective ground that were previously out only on the separate power unit.

Install integrated or built-in power supplies are also often used when multiple voltages are required, such as in computers, TVs, VCRs, fax machines or laser printers.

DC Switching Converters

Power supplies also come to DC systems (aircraft, motor vehicles, solar systems ) to be used when voltages must be transformed or AC voltage is required. However, they are not usually referred to as the power supply.

One example is in sharp audio amplifiers built-in power supplies for operation on -board vehicle voltage system, producing voltages of often more than ± 40 V for the output stages of 12 V ( vehicle power). There DC / DC switching power supplies are used, which contain an inverter and a transformer with subsequent rectification.

DC-DC converter are in low-power range used ( less than 5W ) as encapsulated hybrid modules are galvanically isolated supply of assemblies.

Typical applications include line interfaces of telephone modems or network cards, modern PC motherboards and performance graphics cards, the produce from the voltages supplied by PC power supply their operating voltages as close to the consumer (English point- of-load converter ).

Inverters produce AC line voltage from DC voltage networks, eg as a plug-in power adapter in vehicles or fixed installations in DC networks of solar systems.

Utility frequency Laserdiode EIAJ connector
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