Key Points
Power supplies convert one form of energy into another to ensure correct voltage, frequency, and current for connected devices. DC power supplies provide direct current to electronic devices, while AC power supplies provide alternating current at a given frequency and voltage. Switched-mode power supplies work by switching between different operating states to decrease input source‘s average output voltage and current requirement. Uninterruptible power supplies provide continuous electrical energy even during power failures or disruptions, often used in hospitals, data centers, and other critical applications. High-voltage power supplies produce extremely high voltages for specialized equipment like X-ray generators and electron microscopes.
Power supplies are integral to any electrical system and come in many forms. They provide a steady, regulated power supply to ensure connected devices remain safe and functioning correctly. Depending on the application, the type of power supply used can vary greatly. Each type has its advantages and disadvantages depending on the task at hand.
Understanding these differences is critical to selecting the correct type of power supply for your project or application. Below is an in-depth overview of the various power supplies available and their applications.
What Is a Power Supply?
A power supply is a device that supplies safe and regulated electrical energy to an electrical load. Its primary function is converting one form of energy into another to ensure correct voltage, frequency, and current. Typically, the units convert AC power into a lower DC voltage for use in electronics, computers, and other devices. Thus, power supply units are sometimes called electric power converters.
Other functions performed by power supplies include:
- Shutting off the current flow in case of an electrical fault.
- Regulating and limiting the amount of power drawn by appliances to safe levels.
- Power conditioning that prevents voltage surges and electronic noise from reaching the power load.
- Power-factor correction functions.
- Storing energy to continue powering devices in case of a temporary power interruption.
While some power supply units come as separate standalone equipment, others are built into the appliances they power. Examples of built-in power supplies include those available in consumer electronic devices and desktop computers.
Types of Power Supply
Here are the main types of power supply.
1. DC Power Supply
DC Output: 12V
DC Amp Output: 13A
Max output: 156W
AC Input: 85 – 264 VAC
Only one output at a time
DC power supplies provide direct current (DC) to the load. They are usually present in electronic devices, such as computers, medical equipment, and household appliances. In many cases, DC power supplies convert AC input voltage into lower DC output voltage with the help of a transformer or suitable device. However, depending on the requirements, AC-to-DC power supplies occasionally give output voltage with negligible alternating current frequency, known as a ripple voltage.
Besides AC-to-DC power supply units, you can also find DC-to-DC power supplies that help to convert one DC voltage into another. These serve applications such as electric vehicles and battery-powered devices, where the output voltage must differ from the input voltage.
2. Linear Power Supply
DC output: 12V
AC input: 85 to 256V
Power: 48W
Fixed, singular output
Linear power supplies are the most common type of AC-to-DC converter. A liner power supply unit obtains DC output voltage by passing the AC input voltage through a power transformer for filtering and rectification. Through filtering, the power supply decreases the amplitude of the AC mains frequency in the rectifier output.
The load‘s ripple tolerance often dictates the amount of filtering required from the power supply. However, in certain instances, it is ignored entirely. For example, some battery charging applications only need a power supply with just a diode, transformer, and simple resistors to limit the output charging current.
3. Switched-Mode Power Supply
Output: 300 to 400 W
Output Voltage: 48V
continuous output
Switched-mode power supply (SMPS) units are the second most common type of AC-to-DC power supply. As its name suggests, an SMPS works by switching between different operating states to decrease the input source‘s average output voltage and current requirement. This type of power supply rectifies the AC input directly and filters it in order to acquire a DC voltage.
The SMPS then switches the resulting DC voltage off and on, electronically switching circuitry at a high frequency. As a result, it produces an alternating current that can pass through a high-frequency inductor or transformer. After the transformer or inductor, the high-frequency alternating current is filtered and rectified to create the ideal DC output voltage.
For safety reasons, the SMPS sometimes uses adequately insulated high-frequency transformers to ensure the output is electrically insulated from its mains. They also have other safety features, like current limits, to protect users and equipment from harm. SMPS are typically regulated and often use feedback controllers to monitor the load‘s current draw and keep the output DC voltage constant.
If an SMPS detects a high-current unnatural power drain, it can assume it to be a direct short and shut down before any harm occurs.
4. Capacitive (Transformerless) Power Supply
TRANSFORMERLESS Power Supply Unassembled Kit [FK817]
AC Input: 220 or 110 V
DC Output: 6 or 9 V
Accepted current: 20 to 50 mA
Includes PDB (5 x 3 x 1.7 cm)
Capacitive (transformerless) power supply units are the last type of AC-to-DC converters. They work by converting the input voltage into a rectified waveform without a transformer, using capacitors instead. They use capacitors to reduce the mains input voltage to a lesser AC voltage and filter, regulate, and rectify it to produce a consistent DC output voltage.
The resultant output voltage and the mains are not isolated. Therefore, anything connected to a capacitive power supply must have reliable insulation to protect the equipment and people from deadly high voltage. Additionally, its voltage reduction capacitor must have the capacity to withstand the full mains voltage and support the maximum load current. These constraints limit the capacitive power supply applications to only low-power applications.
5. Linear Regulator
Bridgold 20pcs L7805CV L7805 Linear Voltage Regulator
Connection type: 3-pin
Output voltage: 5V
Output current: 1.5A
Features protection against short circuits
A linear regulator is an electronic device used in a power supply to control the output voltage. Its primary function is to convert differing DC voltage to a constant lower DC voltage. It also performs current-limiting tasks that protect the load and power supply from excessive and potentially destructive currents.
Experts recommend using a linear voltage regulator with other power supplies to maintain a steady output voltage, independent of input voltage fluctuations and load impedance. Liner voltage regulators also help reduce noise and the output voltage‘s magnitude and ripple.
6. AC Power Supply
AC Input: 110 to 120 VAC
output: 12V
Includes multiple safety features
Output current: 1500mA
AC power supplies provide alternating current (AC) output at a given frequency and voltage. They typically receive voltage from the main wall outlets, often incompatible with the power needed to power a load. AC power supplies fine-tune and transform the power input into the current, frequency, and voltage required by the appliance to address this issue.
AC power supplies transform the power input by stepping the voltage up or down, followed by filtering. Consequently, the power supplied reaches the load in a controlled and correct manner. In a nutshell, AC power supplies can regulate an appliance‘s power voltage and current to achieve safe levels.
The source power input can be in DC or AC form with AC power supplies. Depending on the application, a single power supply can provide both AC and DC outputs. Occasionally, some AC power supply transformers may give voltage output similar to the source voltage, known as isolation transformers.
7. AC Adapter
TMEZON Power Adapter Usb Supply AC to DC
Cord length: 8 feet
DC output: 12 V
Output current: 2A
Short circuit, Over voltage, Over current protection built in
AC adapters are power supplies called "plug-in adapters" or "plug packs." These adapters come built into alternating current main power plugs with DC or AC output conveyed over one or more hard-wired cables. Universal AC adapters accommodate different AC source voltages using interchangeable input connectors.
Adapters with AC outputs often only have a passive transformer, while DC-output adapters have a few diodes or employ switch-mode circuitry. One unique feature of AC adapters is that they consume power and produce magnetic and electric fields even when unconnected to any load. Therefore, plugging them into power strips is often necessary to ensure users can turn them on and off conventionally.
8. Programmable Power Supply
Hantek Programmable DC Power Supply
Output voltage: up to 160v DC
Output current: up to 4A
Features adjustable output voltage and current
Includes 10 memory slots
Programmable power supplies (PPS) are the latest type of AC-to-DC power supply units. PPSs allow remote-controlled operations through a digital interface or analog input. They provide high accuracy, flexibility, and control to the user by allowing them to adjust the output voltage and current according to their needs programmatically.
Programmable power supplies commonly operate in automated test instruments like digital multimeters, crystal growth monitoring, oscilloscopes, and X-ray generators. This type of power supply typically uses an integral microcomputer to monitor and control supply operation. They also come fitted with a computer interface that may use standard or proprietary communication protocols alongside device control languages.
9. Uninterruptible Power Supply
APC UPS Battery Backup and Surge Protector
Power cord length: 5 feet
Capacity: 330W (600VA)
Includes 7 NEMA outlets and 1 USB port
Features surge protection (only on 2 outlets)
Uninterruptible power supplies (UPS) are power systems that provide a continuous flow of electrical energy to a load, even in the event of an electricity failure or disruption. UPSs typically receive power from more than one source simultaneously. Moreover, they usually receive power from AC mains directly while simultaneously charging a storage battery.
The storage battery takes over instantaneously in case of a blackout or power failure to ensure an uninterrupted power supply to the load. These power supplies store the energy from an AC source and convert it into DC voltage. A UPS also protects against overvoltage, under-voltage, and other irregularities in the power supply. Further, these systems may also contain surge protection elements to protect against spikes of high voltage that can damage sensitive equipment.
The duration of power provided by a UPS often depends on the size of its battery. Typically, most computer installations provide power for only enough time for the users to save their data and shut down the system properly.
However, some UPS systems have unique designs that allow them to provide power for extended periods, from 15 minutes to hours or days. Such UPSs often use a turbine or an internal combustion engine to provide power for hours. UPSs like this perform various functions in hospitals, call centers, data centers, and cell sites where power supply disruptions can have severe consequences.
10. High-Voltage Power Supply
DC Output voltage: 5 to 30 KV
Power: 300W
AC Input voltage: 180 to 250 V
Features shortcut protection and spark prevention
High-voltage power supplies are incredibly complex power conversion circuits designed to convert from a lower to a higher voltage potential. These circuits produce extremely high voltages ranging from tens to hundreds of kilovolts. They are typically used to manipulate and accelerate ion beams and electrons in equipment like X-ray generators, focused ion beams, and electron microscopes.
High-voltage power supplies use special connectors to prevent arcing, accidental human contact, or insulation breakdown. Federal Standard connectors are critical for anything above 20kV, but regular connectors are allowed for lower voltages. To control the output voltage, some high-voltage power supplies use a digital or analog input communication interface.
High-voltage power supplies often apply their energy input to a power inverter, which drives a high-voltage transformer and a voltage multiplier to produce higher voltages. The high voltage produced then passes through special connectors to a voltage divider, which converts it to a low-voltage metering signal. A closed-loop controller uses this metering signal to regulate the generated high voltage by adjusting the inverter input power.
11. Bipolar Power Supply
Bipolar power supplies generate positive and negative voltages from a single AC source. They operate on all four quadrants of the current/voltage on the Cartesian plane. Although a low-level analog signal controls the output, the bipolar power supply is a low-bandwidth operational amplifier with seamless zero-crossing and high output power. Bipolar power supplies typically operate in scientific applications to power magnetic devices.
Bottom Line
Understanding the different types of power supply units is crucial for selecting the right one for your specific needs. Whether you require a standard ATX power supply for your computer, a DC power supply for electronics projects, or a modular power supply for enhanced flexibility, each type offers unique features and benefits. Identifying the most suitable power supply ensures your applications and devices operate reliably and safely.
