Umair Gaines
The term 'supply' in electrical terms refers to the provision of electricity, which is a form of energy that can be transmitted through wires and is used for various purposes, including heating, lighting, and powering machines. Electricity supply involves delivering energy in the form of electric current from a source to a load, such as an electrical outlet, battery, or generator. Power supplies can be categorized in different ways, including functional features, and they play a crucial role in regulating voltage, limiting current, and ensuring safe and uninterrupted power delivery.
Characteristics and Values of Electrical Supply:
| Characteristics | Values |
|---|---|
| Definition | To supply electricity is to provide a form of energy that can be carried by wires and used for heating, lighting, and powering machines. |
| Sources | Electrical supply sources include the electric power grid, batteries, fuel cells, generators, solar power converters, and other power supplies. |
| Functions | Power supplies can limit current to safe levels, shut off the current in an electrical fault, condition power to prevent voltage surges, and store energy to power loads during interruptions. |
| Categories | Regulated, unregulated, adjustable, and isolated power supplies. |
| Types | Bench, open frame, rack mount, integrated, and external power supplies. |
| High-Voltage Applications | X-ray generators, electron microscopes, focused ion beam columns, electrophoresis, and electrostatics. |
| Standards | Set by the International Electrotechnical Commission (IEC) and tested for electromagnetic and electrostatic discharge immunity. |
| Safety | AC adapters may be "electricity vampires," always consuming power, while external power supplies are considered safer for consumer electronics by reducing high-voltage mains current. |
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What You'll Learn
- Power supply types: regulated, unregulated, adjustable, isolated, high-voltage
- Power supply functions: limiting current, shutting off current, power conditioning, power-factor correction
- Power input sources: electric power grid, batteries, generators, solar power converters
- Power supply performance curves: efficiency vs. load, input current vs. line input
- Power supply standards: International Electrotechnical Commission, electromagnetic compatibility
Power supply types: regulated, unregulated, adjustable, isolated, high-voltage
Power supplies adapt the type of power available, either direct current (DC) or alternating current (AC), to the required form and voltage for a specific use. Power supplies can be broadly classified into two categories: regulated and unregulated.
Regulated Power Supply
A regulated power supply converts unregulated AC (alternating current) into a constant DC. It functions to supply a stable voltage (or less often current) to a circuit or device that must be operated within certain power supply limits. The output from the regulated power supply may be alternating or unidirectional, but is almost always DC. The type of stabilization used may be restricted to ensuring that the output remains within certain limits under various load conditions, or it may also include compensation for variations in its own supply source. The latter is much more common today.
Regulated power supplies have an added voltage regulator, which reduces the ripple voltage for even electricity from the supply. The exact operation of regulated power supplies depends on whether they are linear or switching. Linear power supplies produce only very little noise (or "ripple voltage") and are less prone to external electromagnetic and radio frequency interference (EMI, RFI), making them preferable for audio equipment and radio-related applications and for powering delicate circuitry. Linear power supplies also have fewer failable parts, increasing longevity, and have a quicker transient response. On the other hand, switching-mode power supplies are more lightweight, efficient, and more compact at a similar power rating, making them suitable for high-power applications.
Unregulated Power Supply
While the energy from an unregulated power supply stays constant, the voltage output can drop or rise unexpectedly with a shift in the load current or the input voltage. Unregulated power supplies have a design that delivers the expected output at a given current but does not always reflect the actual voltage output. These power supplies are simple, low-cost options with the major disadvantage of providing uneven voltage.
Adjustable Power Supply
Some power supplies have variable regulators, allowing for adjustment of the output voltage. These can be adjusted with rotary knobs, each usually with a "coarse" and "fine" knob.
Isolated Power Supply
When a power supply is listed as isolated, it is normally referring to input to output isolation. An isolated power supply provides a clear barrier across which dangerous voltages won't pass, providing safety. They are typically used in applications that have to meet safety and system requirements, such as medical devices.
High-Voltage Power Supply
High-voltage power supplies are used in a variety of applications, including the semiconductor industry and plasma power delivery systems. They offer high power solutions with output power ratings up to 10 kW.
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Power supply functions: limiting current, shutting off current, power conditioning, power-factor correction
In electrical terms, a power supply is a device that provides electrical energy to a load, such as an electronic device or a circuit. Power supplies can be classified into different types, including linear and switch-mode power supplies, and they play a crucial role in various electronic applications.
Limiting Current
Current limiting is a critical function of power supplies, protecting the circuit from harmful effects due to short circuits or overloads. Current limiter circuits restrict the maximum current delivered to the load, preventing damage to both the power supply and the circuit being powered. This is especially important in regulated power supplies, where constant current limiting or foldback current limiting techniques are employed to maintain safe power dissipation levels.
Shutting Off Current
While not explicitly mentioned in the provided topics, shutting off the current is typically achieved through current limiter circuits or overcurrent protection devices. These mechanisms interrupt the current flow in the event of a fault or overload condition, safeguarding the circuit from potential damage.
Power Conditioning
Power conditioning refers to the process of ensuring that the electrical power supplied to a load is stable, clean, and free from disturbances. This includes reducing electromagnetic interference (EMI), which can impair the performance of electronic devices, and maintaining the desired voltage and current levels to ensure the proper functioning of the load.
Power-Factor Correction
Power-Factor Correction (PFC) is a technique used to improve the efficiency of alternating current (AC) power systems. It involves adding capacitors or inductors in parallel with the coil to reduce reactive power consumption and improve the power factor, which is the ratio of real power to apparent power. Active PFC, passive PFC, and hybrid PFC methods are employed depending on the specific power requirements and load conditions, with active PFC being the most commonly used due to its accuracy, adaptability, and compact size.
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Power input sources: electric power grid, batteries, generators, solar power converters
An electrical grid, or electricity network, is an interconnected network for electricity delivery from producers to consumers. Electrical grids consist of power stations, electrical substations to adjust voltage, electric power transmission to carry power over long distances, and finally, electric power distribution to customers. Electrical grids vary in size and can cover entire countries or continents.
The power output of generators on the grid is the production of the grid, typically measured in gigawatts (GW). Power stations are typically built close to energy sources and far from densely populated areas. Sources of primary energy for power grids include electromechanical generators driven by heat engines from fossil, nuclear, and geothermal sources or driven by the kinetic energy of water or wind. Other power sources include photovoltaics driven by solar insolation and grid batteries.
Grid energy storage, or large-scale energy storage, is a collection of methods used for energy storage within an electrical power grid. Electrical energy is stored when electricity is plentiful and inexpensive, especially from intermittent power sources such as renewable electricity from wind, tidal, and solar power, and then generated when demand is high and electricity prices are higher. Grid energy storage helps to smooth local fluctuations of wind and solar energy, making it a key technology to mitigate global warming.
Battery storage has enabled commercially viable projects to store energy during peak production and release it during peak demand. Batteries are also used as portable power sources and can be recharged through external power sources such as wall adapters or power grids. Efficient circuits have been designed to smoothly switch between battery and external power sources without switching noise.
Generators are another power input source and can be used as portable power stations or for standby power generation. Solar-powered generators are also available and utilize solar energy to provide electricity.
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Power supply performance curves: efficiency vs. load, input current vs. line input
In electrical engineering, a power supply is a component that provides energy in the form of electric current from a source to a load. Power supplies are an essential part of many electronic devices and systems, providing the necessary electrical energy for their operation.
Power Supply Performance Curves: Efficiency vs. Load
The efficiency of a power supply is the output power divided by the input power, as there is typically some power loss during the AC to DC conversion. The efficiency of a power supply can be plotted on a curve, known as an efficiency curve, which illustrates how the efficiency varies with different input voltages and load conditions. The x-axis typically represents the power supply load, while the y-axis represents efficiency.
The efficiency of a power supply is not constant and can change depending on various factors. For example, efficiency tends to decrease at lighter output loads due to internal fixed losses from the control circuitry or internal fan, and the effect of the switch-mode converter running at a sub-optimal pulse width. Additionally, the output voltage of the power supply can also impact efficiency, with lower output voltage models requiring different output rectification techniques to minimise losses.
Input Current vs. Line Input
The input current of a power supply refers to the current drawn by the supply, which can be measured under different input voltage and output load conditions. The relationship between input current and line input voltage can be illustrated using a performance curve. This curve demonstrates how the input current varies with different line input voltages, providing valuable information about the power supply's behaviour under different conditions.
By understanding these performance curves, engineers and designers can make informed decisions about power supply selection, ensuring that the power supply is suitable for the intended load and input voltage conditions.
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Power supply standards: International Electrotechnical Commission, electromagnetic compatibility
In electrical terms, a power supply refers to a device that provides electric energy to an output load or load device, which can be machinery or any electrical system. Power supplies are connected to a source of energy, which could be an electrical power grid, battery, generator, or solar power converter, and convert this energy into a form that can be used by the output load.
The International Electrotechnical Commission (IEC), based in Geneva, is the primary international organisation that creates and publishes regulatory safety standards for electronic products and components. IEC standards cover a wide range of technologies within electrotechnology, and while they do not conduct any testing, their standards are typically accepted or modified and then accepted by worldwide national safety agencies.
One of the key IEC standards is electromagnetic compatibility (EMC), which relates to the compliance of a power supply and its components with standards for electromagnetic emissions and susceptibility (immunity). Electromagnetic compatibility ensures that electronic products do not interfere with each other's performance through the transmission or reception of unintentional electronic signals, known as electromagnetic interference (EMI).
EMI and EMC standards are often regulated by local governments, with the FCC (Federal Communications Commission) governing EMI and EMC in the US, and the EU following the Electromagnetic Compatibility (EMC) Directive 2014/30/EU. Countries outside of the US and EU typically harmonise their standards with either the FCC or the EU EMC Directive.
IEC standards also cover a range of other areas, including:
- Minimum requirements for grid-connected photovoltaic systems
- Internet protocol (IP) and transport stream (TS)-based service access
- Safety requirements for power electronic converter systems and equipment
- Nuclear power plants – instrumentation and control software
- Power cables with extruded insulation and their accessories for rated voltages above 30 kV up to 150 kV
- Electromagnetic compatibility for electrical and electronic installations in ships with metallic hulls
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Frequently asked questions
An electrical supply is a source of electricity, which is a form of energy that can be carried by wires and is used for heating, lighting, and providing power for machines.
An electrical supply has a power input connection that receives energy in the form of electric current from a source. This source could be the electric power grid, batteries, generators, solar power converters, or another power supply. The electrical supply then delivers current through one or more power output connections to the load, which could be a machine or another piece of equipment.
Examples of electrical supplies include high-voltage power supplies used in equipment such as x-ray generators and electron microscopes, AC adapters (also known as "plug packs" or "wall warts"), and bench power supplies used for circuit testing and development.
