Mar 26, · A DC power supply is a device that supplies electric energy of fixed polarity, either positive or negative. "DC" in this context means "direct current." Direct current is an alternative to alternating current, frequently shortened to "AC." Power supplies take energy from a power input and deliver it to a power output. Basics. Direct Current (DC) Power refers to the unidirectional flow of electrons and is the form of power that is most commonly produced by sources such as solar cells and batteries.
Due to their ability to provide power in different ways, AC and DC power have long been embroiled in a battle for supremacy. However, the two appear to be more recently coming together to exist in harmony.
Alternating and reversing direction 60 times per second 50 in EuropeAC current could be converted to different voltages more easily using a transformer.
However, in recent years, DC has seen a bit of a renaissance. While both AC and DC current deliver electricity, the way in which that electricity arrives at its end destination differs. What are your appliances and electronics eating? Homes and businesses across the nation will continue to be powered predominantly by AC power. With the rise of What is dc power supply definition, solar cells, electric vehicles, and mobile electronics, however, advancements in DC are on the rise, with methods continually under development for transporting and converting DC to higher and lower voltages with less electricity loss.
The couple working side-by-side in homes and businesses across the U. Give peace a chance with an electrical box or service upgrade from Mr. Electric today. Want to know more about electrical current? Check out this blog on electrical troubleshooting from Mr. What is dc power supply definition, a Neighborly company. Skip to main content. Your health and safety are our what does kyoya mean in japanese priority during this time.
Click here for our precautionary measures. AC Your home or office receives electricity in the form of wave-like AC current, which is capable of changing direction and voltage from higher to lower current with the aid of transformers. DC The consistent and constant voltage of What are acetaminophen tablets used for power supplies electronics that use a battery, such as your mobile device or smartphone.
This blog is made available by Mr. Electric for educational purposes only to give the reader general information and a general understanding on the specific subject above. The blog should not be used as a substitute for a licensed electrical professional in your state or region. Check with city and state laws before performing any household project.
What is power?
DC The consistent and constant voltage of DC power supplies electronics that use a battery, such as your mobile device or smartphone. Like the battery powering your kid’s remote control car, the smooth, steady electrical current of DC power always flows in the same direction, between positive and negative terminals. AC/DC. Direct current (DC) power uses electrons that move in a straight line. This linear movement, in contrast to AC’s wave motion, gives this current its name. This form of current comes from batteries, solar cells, fuel cells, alternators equipped with commutators that create direct energy, and rectifiers that convert from AC to DC power.
A power supply is an electrical device that supplies electric power to an electrical load. The primary function of a power supply is to convert electric current from a source to the correct voltage , current , and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.
Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault , power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction , and storing energy so it can continue to power the load in the event of a temporary interruption in the source power uninterruptible power supply.
All power supplies have a power input connection, which receives energy in the form of electric current from a source, and one or more power output connections that deliver current to the load.
The source power may come from the electric power grid , such as an electrical outlet , energy storage devices such as batteries or fuel cells , generators or alternators , solar power converters, or another power supply.
The input and output are usually hardwired circuit connections, though some power supplies employ wireless energy transfer to power their loads without wired connections. Some power supplies have other types of inputs and outputs as well, for functions such as external monitoring and control. Power supplies are categorized in various ways, including by functional features.
For example, a regulated power supply is one that maintains constant output voltage or current despite variations in load current or input voltage. Conversely, the output of an unregulated power supply can change significantly when its input voltage or load current changes. Adjustable power supplies allow the output voltage or current to be programmed by mechanical controls e. An adjustable regulated power supply is one that is both adjustable and regulated. An isolated power supply has a power output that is electrically independent of its power input; this is in contrast to other power supplies that share a common connection between power input and output.
Power supplies are packaged in different ways and classified accordingly. A bench power supply is a stand-alone desktop unit used in applications such as circuit test and development. Open frame power supplies have only a partial mechanical enclosure, sometimes consisting of only a mounting base; these are typically built into machinery or other equipment.
Rack mount power supplies are designed to be secured into standard electronic equipment racks. An integrated power supply is one that shares a common printed circuit board with its load. An external power supply, AC adapter or power brick , is a power supply located in the load's AC power cord that plugs into a wall outlet; a wall wart is an external supply integrated with the outlet plug itself. These are popular in consumer electronics because of their safety; the hazardous or volt main current is transformed down to a safer voltage before it enters the appliance body.
Power supplies can be broadly divided into linear and switching types. Linear power converters process the input power directly, with all active power conversion components operating in their linear operating regions. In switching power converters, the input power is converted to AC or to DC pulses before processing, by components that operate predominantly in non-linear modes e.
Power is "lost" converted to heat when components operate in their linear regions and, consequently, switching converters are usually more efficient than linear converters because their components spend less time in linear operating regions. Depending on application requirements the output voltage may contain large or negligible amounts AC frequency components known as ripple voltage , related to AC input voltage frequency and the power supply's operation.
This section focuses mostly on the AC-to-DC variant. In a linear power supply the AC input voltage passes through a power transformer and is then rectified and filtered to obtain a DC voltage. The filtering reduces the amplitude of AC mains frequency present in the rectifier output and can be as simple as a single capacitor or more complex such as a pi filter.
The electric load's tolerance of ripple dictates the minimum amount of filtering that must be provided by the power supply. In some applications, ripple can be entirely ignored.
For example, in some battery charging applications, the power supply consists of just a transformer and a diode, with a simple resistor placed at the power supply output to limit the charging current.
The resulting DC voltage is then switched on and off at a high frequency by electronic switching circuitry, thus producing an AC current that will pass through a high-frequency transformer or inductor. Switching occurs at a very high frequency typically 10 kHz — 1 MHz , thereby enabling the use of transformers and filter capacitors that are much smaller, lighter, and less expensive than those found in linear power supplies operating at mains frequency.
After the inductor or transformer secondary, the high frequency AC is rectified and filtered to produce the DC output voltage. If the SMPS uses an adequately insulated high-frequency transformer, the output will be electrically isolated from the mains; this feature is often essential for safety. Switched-mode power supplies are usually regulated, and to keep the output voltage constant, the power supply employs a feedback controller that monitors current drawn by the load.
The switching duty cycle increases as power output requirements increase. SMPSs often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm. PC power supplies often provide a power good signal to the motherboard; the absence of this signal prevents operation when abnormal supply voltages are present.
Some SMPSs have an absolute limit on their minimum current output. In a no-load condition the frequency of the power slicing circuit increases to great speed, causing the isolated transformer to act as a Tesla coil , causing damage due to the resulting 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-power dummy load such as a ceramic power resistor or watt light bulb can be attached to the supply to allow it to run with no primary load attached.
The switch-mode power supplies used in computers have historically had low power factors and have also been significant sources of line interference due to induced power line harmonics and transients. In simple switch-mode power supplies, the input stage may distort the line voltage waveform, which can adversely affect other loads and result in poor power quality for other utility customers , and cause unnecessary heating in wires and distribution equipment.
Furthermore, customers incur higher electric bills when operating lower power factor loads. To circumvent these problems, some computer switch-mode power supplies perform power factor correction, and may employ input filters or additional switching stages to reduce line interference. A capacitive power supply transformerless power supply uses the reactance of a capacitor to reduce the mains voltage to a smaller AC voltage.
Typically, the resulting reduced AC voltage is then rectified, filtered and regulated to produce a constant DC output voltage. The output voltage is not isolated from the mains.
Consequently, to avoid exposing people and equipment from hazardous high voltage, anything connected to the power supply must be reliably insulated. The voltage reduction capacitor must withstand the full mains voltage, and it must also have enough capacitance to support maximum load current at the rated output voltage.
Taken together, these constraints limit practical uses of this type of supply to low-power applications. The function of a linear voltage regulator is to convert a varying DC voltage to a constant, often specific, lower DC voltage.
In addition, they often provide a current limiting function to protect the power supply and load from overcurrent excessive, potentially destructive current. A constant output voltage is required in many power supply applications, but the voltage provided by many energy sources will vary with changes in load impedance.
Furthermore, when an unregulated DC power supply is the energy source, its output voltage will also vary with changing input voltage. To circumvent this, some power supplies use a linear voltage regulator to maintain the output voltage at a steady value, independent of fluctuations in input voltage and load impedance. Linear regulators can also reduce the magnitude of ripple and noise on the output voltage.
An AC power supply typically takes the voltage from a wall outlet mains supply and uses a transformer to step up or step down the voltage to the desired voltage. Some filtering may take place as well. In some cases, the source voltage is the same as the output voltage; this is called an isolation transformer. Other AC power supply transformers do not provide mains isolation; these are called autotransformers ; a variable output autotransformer is known as a variac. Other kinds of AC power supplies are designed to provide a nearly constant current , and output voltage may vary depending on impedance of the load.
In cases when the power source is direct current, like an automobile storage battery , an inverter and step-up transformer may be used to convert it to AC power. Portable AC power may be provided by an alternator powered by a diesel or gasoline engine for example, at a construction site, in an automobile or boat, or backup power generation for emergency services whose current is passed to a regulator circuit to provide a constant voltage at the output.
Some kinds of AC power conversion do not use a transformer. If the output voltage and input voltage are the same, and primary purpose of the device is to filter AC power, it may be called a line conditioner. If the device is designed to provide backup power, it may be called an uninterruptable power supply.
In modern use, AC power supplies can be divided into single phase and three phase systems. An AC adapter is a power supply built into an AC mains power plug. AC adapters are also known by various other names such as "plug pack" or "plug-in adapter", or by slang terms such as "wall wart". AC adapters typically have a single AC or DC output that is conveyed over a hardwired cable to a connector, but some adapters have multiple outputs that may be conveyed over one or more cables.
Adapters with AC outputs may consist only of a passive transformer plus a few diodes in DC-output adapters , or they may employ switch-mode circuitry. AC adapters consume power and produce electric and magnetic fields even when not connected to a load; for this reason they are sometimes known as "electricity vampires", and may be plugged into power strips to allow them to be conveniently turned on and off.
A programmable power supply is one that allows remote control of its operation through an analog input or digital interface such as RS or GPIB. Controlled properties may include voltage, current, and in the case of AC output power supplies, frequency. They are used in a wide variety of applications, including automated equipment testing, crystal growth monitoring, semiconductor fabrication, and x-ray generators. Programmable power supplies typically employ an integral microcomputer to control and monitor power supply operation.
Power supplies equipped with a computer interface may use proprietary communication protocols or standard protocols and device control languages such as SCPI.
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 battery instantly takes over so that the load never experiences an interruption. Instantly here should be defined as the speed of electricity within conductors which is somewhat near the speed of light. Some manufacturers use a quasi standard of 4 milliseconds.
However, with high speed data even 4 ms of time in transitioning from one source to another is not fast enough. The transition must be made in a break before make method.
How much time the UPS will provide is most often based on batteries and in conjunction with generators. That time can range from a quasi minimum 5 to 15 minutes to literally hours or even days.
In many computer installations, only enough time on batteries to give the operators time to shut down the system in an orderly way. Other UPS schemes may use an internal combustion engine or turbine to supply power during a utility power outage and the amount of battery time is then dependent upon how long it takes the generator to be on line and the criticality of the equipment served.
Such a scheme is found in hospitals, data centers, call centers, cell sites and telephone central offices. A high-voltage power supply is one that outputs hundreds or thousands of volts.
A special output connector is used that prevents arcing , insulation breakdown and accidental human contact. Federal Standard connectors are typically used for applications above 20 kV, though other types of connectors e. Some high-voltage power supplies provide an analog input or digital communication interface that can be used to control the output voltage.