AC DC Power Supply: Types, Principles and Benefits

Chapter 1: Understanding the Basics of AC and DC Power Supplies

This chapter discusses fundamental topics including the idea of a power supply, characteristics and functions of AC and DC power supplies, and the construction and operation of AC/DC power sources.

Defining a Power Supply

A power supply is a device or circuit that translates electricity from the mains or different sources into precise voltage and current levels required for specific apparatus. These apparatus range from common household devices to large industrial machinery.

Each electrical device has certain voltage and current specifications necessary for proper functionality, usually indicated by the manufacturer. If these conditions aren't satisfied, the device might not function or could incur damage if exceeded. Some power supplies can cater to multiple devices at once, needing to maintain a steady output regardless of load or input variations, known as regulated power supplies. In contrast, unregulated power supplies' outputs fluctuate with input changes, as their output is a fixed portion of the input. Power supplies may appear as external units like chargers or as internal components in devices such as TVs and radios. They can convert both AC or DC input to DC or AC output.

Exploring AC and DC Power Supplies

Direct current (DC) ensures a steady flow in one direction, typically provided by sources like batteries and solar panels.

Alternating current (AC) shifts between positive and negative cycles, altering the electrons' direction of flow intermittently.

This describes electric current as delivered from a generator or power outlet. Electricity generated in power plants and transmitted to homes is provided as alternating current.

Direct current (DC) retains a stable voltage, flowing in a singular path. Alternating current (AC), on the other hand, involves a voltage that reverses, causing the current to change its directional flow as well.

Attributes of AC/DC Power Supplies

In alternating current (AC), the current's direction continuously switches. If inductors or capacitors exist in the circuit, a phase shift might occur, leading the current to behave differently than the voltage. In contrast, both current and voltage in direct current (DC) maintain stability, ensuring component behavior remains predictable without phase shifts.

In AC circuits, because the current direction alternates, not all of it may reach the load, with some energy oscillating between the source and load, resulting in reactive power. With DC, the current flows unidirectionally, ensuring all current courses through the load, avoiding reactive power and optimizing power use.

Interrupting a DC circuit can be challenging, especially when a constant high voltage is involved, posing risks such as sparks. AC, which periodically reaches zero as the voltage alternates, tends to be safer to interrupt.

To alter DC voltage, it often undergoes conversion to AC and back again to DC, necessitating specialized equipment. Direct current is largely produced by storage means like batteries and best suits battery-dependent gadgets.

Though AC is prevalent in residential environments, electronic gadgets like computers and televisions rely on DC. AC is converted to DC via rectifiers in these devices. In settings like data centers, direct current use is advocated to prevent conversion-associated losses.

Building AC/DC Power Supplies

Each AC-DC power supply is crafted uniquely. Here are standard design elements commonly considered:

Functional Capabilities of AC/DC Power Supplies

AC-DC power supplies vary based on their functional capabilities. Regulated power supplies offer consistent output regardless of load or input fluctuations. Unregulated power supplies have outputs that change with load or input alterations. Adjustability is a feature enabling users to set the output using controls like knobs or electronic inputs. Adjustable regulated power supplies combine regulation with flexibility. Isolated power supplies provide output that is electrically distinct from the input power, unlike others which have shared connections.

Variety in Power Supply Packaging

Power supplies have diverse packaging styles. Bench power supplies are stand-alone units used mainly in testing and developmental contexts. Open frame power supplies lack full mechanical covers, usually integrated within machinery. Rack mount power supplies are tailored to fit standard equipment racks, providing protection. Integrated power supplies share a circuit board with their load. External power supplies, recognized as AC adapters, are integrated within device power cords. Wall warts are compact external supplies incorporated into outlet plugs, optimizing safety by reducing main voltage to safer levels.

Power Conversion Techniques for AC/DC Supplies

AC-DC power supplies are mainly categorized into switching and linear types. Linear supplies process voltages directly, with conversion apparatus working in linear regions. Switching supplies first transform input voltages to AC or DC pulses, using devices primarily in non-linear modes, ensuring devices spend minimal time in linear regions. Consequently, switching supplies are normally more efficient since less energy dissipates as heat compared to linear types.

Operational Dynamics of AC/DC Power Supplies

An AC-DC power supply initially receives an AC voltage of 230V, or a regional equivalent. Inside the unit, this voltage is stepped down to an appropriate level, typically between 9V and 24V for most applications, converting it then to DC. In linear supplies, diodes act on this conversion; switching mode supplies employ transistors. After transitioning to DC, the voltage smoothens out to remove ripples and undergoes regulation. Some supplies might bypass regulation. The resultant DC power activates household electronics, including computers and TVs.

Factors in Selecting an AC/DC Power Supply

AC Input Voltage Range (VIN) – Dictates the necessary AC input voltage range for the power supply, such as single-phase or three-phase AC. Recognizing both the appliance's and the supply's AC voltage range is essential when choosing an appropriate power supply. Many devices operate within a broad input range of 85 to 264 VAC at 47Hz to 60Hz. Some AC-DC power supplies offer interchangeable blades for adaptability to regional requirements.

Output Voltage Range (VOUT) – Specifies needed output voltage range. If variable voltage is crucial for applications like LED lighting or testing, selecting a power supply with adjustable output provides cost efficiency and convenience. Some uses might require fixed outputs like 12V or 48V.

Maximum Output Current (IOUT) – Understanding the peak current output is key, especially when current outputs may fluctuate. Power supplies capable of being paralleled might be necessary to boost power capacity.

Output Regulation – For applications with risky high output ripple or current fluctuations, especially with load types like motor drives, ensuring solid output regulation is vital.

Space and Dimensions – As power supplies evolve to be more compact, ensure there’s enough room to fit the power supply and any additional elements, like parallel supplies, conduction plates, or cooling fans.

Enclosure and Cooling – Evaluate whether an enclosure with fans or an external cooling system is needed. Numerous power supplies incorporate over-temperature protection to avert heat-related damages.

Temperature Tolerance – Ensure the power supply can withstand extreme temperatures, ranging from -40 degrees Celsius to +50 degrees Celsius.

Derating Factors – Consider how environmental conditions, such as temperature and elevation, might affect performance, causing possible power derating.

Compliance Standards – Certain applications necessitate meeting standards like IP20, IP22, or 60601. Many power supplies undergo tests to meet general requirements, carrying certifications like TUV, EN, or UL.

Understanding these parameters is crucial in the process of selecting a suitable power supply to fit specific application needs.

Chapter 2:What are the different types of AC-DC power supplies?

Various types of AC-DC power supplies include:

Unregulated Power Supply

Unregulated power supplies use AC voltage as their input. The AC voltage first passes through a step-down transformer, which reduces the voltage and provides it across the secondary terminals. This voltage is then rectified by a bridge rectifier to convert it into DC voltage. Common output voltages include 9V, 12V, 15V, and 24V. A capacitor is used to smooth out the DC voltage from the rectifier. As indicated by its name, an unregulated power supply lacks a voltage regulator in its circuit.

Any variations in the AC input voltage will directly impact the output voltage of an unregulated power supply. Due to its straightforward design, an unregulated power supply is generally durable and has an efficiency of about 60%. It is commonly used in electromechanical applications that do not require a fixed output voltage, such as powering contactors. The main types of unregulated power supplies include half-wave, full-wave center-tapped, and full-wave bridge rectifier configurations.

Switching AC DC Power Supply

Advancements in semiconductor technology, particularly with fast-switching MOSFETs, have addressed issues like transformer size and voltage regulation found in linear AC DC transformers. This technology increases efficiency and reduces heat dissipation. MOSFETs can switch on and off rapidly even under high currents and voltages.

However, switch mode AC DC power supplies have a more complex design compared to linear AC DC power supplies. To avoid using large step-down transformers, the input voltage is rectified and filtered. A DC chopper (DC to AC converter) then transforms this DC voltage into a high-frequency pulse train, which is subsequently rectified and filtered to produce a DC output. This approach allows the use of smaller transformers that avoid saturation.

Linear AC DC Power Supply

This represents the simplest design for AC DC power supplies. They have long been a reliable method for converting AC power from the grid into DC power for household appliances.

A transformer reduces the AC voltage to a lower, more suitable value for home use. The reduced voltage is then rectified into DC and filtered to remove ripples.

The image above illustrates its structure and the changes in output voltage at each stage. A transformer steps down the main supply voltage from 230V.

The output voltage of the transformer is determined by the turns ratio of the primary to the secondary coil, calculated using the equation Vs/Vp = Ns/Np. Transformer operation relies on electromagnetic induction principles. An alternating current in the primary coil generates a magnetic flux, amplified by the core, to induce an alternating current in the secondary coil. The waveform shape is preserved but with reduced amplitude.

The stepped-down voltage is then passed through a rectifier to remove the negative halves of the waveform. There are two types of rectifiers: half-wave and full-wave.

The half-wave rectifier uses two diodes to eliminate the negative half cycle by restricting current flow in that direction. It conducts current only in the positive direction, resulting in a pulsating DC waveform with zero value during the negative half cycle.

The full-wave rectifier, in contrast, converts negative half cycles into positive ones. It redirects the negative half cycle current to pass through the load in the same direction as the positive current.

After rectification, smoothing is performed to remove ripples from the wave and approximate the DC voltage. The smoothed waveform is then regulated to maintain a constant output level despite variations in input voltage.

Capacitive Transformerless Power Supply

Capacitive power supplies, also known as capacitive droppers, use a capacitor’s capacitive reactance to reduce mains AC voltage. Due to high voltage tolerance requirements and the need for high capacitance to achieve the desired current output, these supplies are practical only for low-power applications.

The capacitance required increases with the current drawn; high-capacitance AC capacitors are bulky and expensive. A capacitive power supply typically includes a rectifier and filter to generate DC current from the reduced AC voltage.

This type of supply features a capacitor (C1) with reactance that limits current flow through the bridge rectifier (D1). A series resistor (R1) with the capacitor (C1) prevents voltage spikes during switching. An electrolytic capacitor (C2) smooths the DC voltage and handles switching currents. The figure shows a voltage regulator made by resistor (R3) and a shunt regulator (Zener diode, IC1). If precise voltage stabilization is not critical, a Zener diode can serve as the regulator. The two-terminal components (R5 and R4) are used as a voltage divider in the circuit above.

AC DC Wall Adaptors

AC DC wall adaptors, also known as wall warts or wall plug-in transformers, convert 120Vac (or 220Vac) to a lower DC voltage. They are commonly used with electronic devices in homes and businesses.

Wall warts and junction boxes can be categorized into the following types:

Wall Plug-ins: Switch-Mode Power Supplies

These AC DC wall adaptors eliminate the need for internal cooling devices, allowing for smaller and lighter designs while keeping heat away from sensitive circuits. They provide a lower and safer output to the end product.

Interchangeable Input Wall Plug-in Power Supplies

These versatile adaptors feature four styles of interchangeable plugs for use in the United Kingdom, European Union, North America, and Australia. They operate at 100-240V input and provide 24W at 5-24 VDC.

JSU Series Power Supply Junction Box

These junction boxes are designed for hard-wiring stationary electronic equipment, reducing tangled cords and minimizing accidental disconnections. They are typically available in 24VDC/0.75A and 12VDC/1.5A models.

AC Power Supplies Wall Plug-ins Level VI

These power supplies meet Level VI efficiency standards set by the U.S. Department of Energy, consuming 25% less power compared to previous 60 Hz models. They are ideal for applications like battery backup systems, security locks, HVAC systems, lighting, and camera controls.

Industrial & Commercial Use DC and AC Wall Plug-ins Power Supplies

Designed for commercial and industrial environments, these wall adaptors are available in unregulated models at 60 Hz. They often require agency approvals due to their numerous agency listings.

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Chapter 3: What are AC DC wall adaptors and what are they commonly used for?

AC DC Wall Adaptors

AC DC wall adaptors, often referred to as wall warts or wall plug-in transformers, are devices designed to convert 120V AC (or 220V AC) into a significantly lower DC voltage. These adaptors are commonly used with electronic devices in both residential and commercial settings.

Wall warts and junction boxes can be categorized into the following types:

Wall Plug-ins: Switch-Mode Power Supplies

AC/DC wall adapters eliminate the need for internal cooling mechanisms in power supplies. This allows the final products to be smaller and lighter while ensuring that heat is kept away from sensitive circuits. As a result, a lower and safer output is provided to the end product.

Interchangeable Input Wall Plug-in Power Supplies

The versatility of AC/DC wall adapters is evident in their use of four different interchangeable plugs, which accommodate regions including the United Kingdom, European Union, North America, and Australia. They support input voltages from 100 to 240V and provide a 24W output with adjustable voltages from 5V to 24VDC.

JSU Series Power Supply Junction Box

JSU Series power supply junction boxes are designed for hard-wiring stationary electronic equipment, which helps avoid the problem of tangled cords that can lead to accidental disconnections. These junction boxes typically offer outputs of 24VDC/0.75A and 12VDC/1.5A.

AC Power Supplies Wall Plug-ins Level VI

AC power supplies meeting Level VI efficiency standards are among the first to achieve this rating from the U.S. Department of Energy. They consume 25% less power compared to older 60 Hz AC power supplies and are ideal for applications such as battery backup systems, security system locks, HVAC systems, lighting, and camera controls.

Industrial & Commercial Use DC and AC Wall Plug-ins Power Supplies

Industrial and commercial DC and AC wall plug-in power supplies are designed exclusively for use in such environments. They operate only at a 60 Hz frequency in unregulated AC/DC models and are equipped with necessary agency approvals to meet regulatory standards.

AC/DC Plug-In Power Supplies

While AC/DC plug-in power supplies and AC/DC wall adapters share similar functions, they differ in certain aspects. AC/DC wall adapters are typically designed for permanent installation in wall outlets and come with fixed voltage and current outputs. These adapters are commonly used to power small electronic devices, such as phone or tablet chargers, and generally offer lower power output. In contrast, AC/DC plug-in power supplies are intended to be plugged into a wall outlet and then connected to a device via a separate cable.

AC/DC plug-in power supplies are available in various types, each with unique features and uses. Some offer adjustable voltage and current outputs, allowing users to tailor the power supply to the specific requirements of their device. This flexibility is useful for devices that require precise voltage and current levels to function correctly. Another variation includes power supplies with interchangeable tips or connectors, which can be swapped out to accommodate different devices. This feature is advantageous for users with multiple devices requiring different power specifications, as it allows for the use of a single power supply for all. Additionally, these power supplies come in different form factors; some are compact and portable, ideal for travel or tight spaces, while others are larger and more powerful, suited for industrial or commercial applications.

AC/DC plug-in power supplies have a wide range of applications in both home and industrial settings. They are commonly used to power devices such as laptops, routers, and game consoles, which demand higher power output compared to smaller devices like phones. These power supplies are also used for charging batteries of portable devices, making them valuable for users who need to keep their gadgets charged while on the move.

In addition to powering electronic devices, AC/DC plug-in power supplies can be used to operate lights, small appliances, and more. This can be particularly beneficial for individuals in areas with unreliable power supplies or those looking to reduce electricity costs. In industrial and commercial environments, these power supplies are employed to power machinery and other equipment, proving essential in settings such as factories, construction sites, and other places where reliable power is critical.

When selecting an AC/DC plug-in power supply, it is crucial to consider the voltage and current requirements of the device being powered to ensure proper functionality. The power supply should deliver the correct voltage and current to meet the device’s needs. Additionally, choosing the appropriate tip or connector for the device is important to ensure a secure connection and avoid potential damage. Portability and durability are also key factors; for travel or mobile use, a compact and lightweight option may be preferable, whereas a rugged and durable model may be needed for industrial or commercial applications.

Maintaining AC/DC plug-in power supplies is essential for their safe and reliable operation. Regularly inspect the cables and connectors for signs of damage or wear, and replace any faulty components promptly. Avoid overloading the power supply to prevent harm to both the device and the power supply itself. Always adhere to the correct voltage and current settings for the device in use. Finally, dispose of outdated or damaged power supplies in an environmentally responsible manner, utilizing local electronic waste disposal programs to ensure proper handling of old power supplies.

Chapter 4: What are the primary applications of AC DC power supplies?

This chapter will explore the various applications and benefits of AC DC power supplies.

Applications of AC DC Power Supplies

Switched-mode power supplies (SMPS) in home appliances like computers often feature universal inputs, allowing them to operate with mains supplies worldwide. However, manual switches for adjusting voltage ranges might still be necessary. SMPS can handle a wide range of power voltages and frequencies.

Cell phone chargers, due to their high volume, are typically cost-sensitive. Initially, linear power supplies were used, but they have since transitioned to more efficient switched-mode power supply designs, such as the ringing choke converter. Recent trends towards lower no-load power consumption have popularized flyback topologies, and primary-side sensing controllers are reducing material costs by eliminating secondary-side components like optocouplers.

Switched-mode power supplies are also used for DC/DC conversion. In vehicles, for instance, heavy trucks with a 24V cranking system may use DC/DC converters to provide 12V for accessories. This setup allows for even distribution of loads across 24V battery cells. In industrial settings, such as telecommunications, power may be distributed at low DC voltages from backup systems, with DC/DC converters supplying the necessary voltages.

Switched-mode power supplies are commonly used as low-voltage supplies for lighting, sometimes referred to as "electronic transformers."

Linear power supplies are often employed in applications where cost is a major concern and efficiency is less critical. They are valued for their simple design and fewer components compared to SMPS. Capacitive power supplies are utilized in low-power applications such as LEDs and small DIY projects due to their simplicity.

Benefits of AC DC Power Supplies

The advantages of AC DC power supplies include:

Unregulated Power Supply

Unregulated power supplies are valued for their simplicity and low cost. They are suitable for applications that do not require precise voltage output. Often, a linear power supply is equipped with an unregulated front stage followed by a voltage regulator.

Switched Mode Power Supply

The primary advantage of a switched-mode power supply is its high efficiency, which can reach up to 96%. This is notably superior to that of linear regulators because the switching transistor generates minimal heat when functioning as a switch.

Additional benefits include a compact size, reduced noise, and lightweight design, achieved by eliminating the need for large line frequency transformers and minimizing heat generation. The standby power loss is often significantly lower compared to traditional transformers. Moreover, the transformer in a switched-mode power supply is more compact than those in standard line frequency transformers (whether operating at 60 Hz or 50 Hz depending on the region) and requires less expensive raw materials, such as copper.

Linear Power Supply

Linear power supplies offer several advantages, including a relatively low cost and a straightforward design. They are known for their simplicity, reliability, and low noise generation, making them cost-effective to produce. The reduced number of components in linear power supplies leads to more streamlined designs and lower manufacturing expenses. These characteristics often make them a preferred choice for engineers and designers.

In accordance with electronics and mechanical guidelines, the fewer components in a linear power supply generally result in fewer potential issues. This inherent simplicity contributes to their increased reliability, which is a significant benefit of using linear power supplies.

Capacitive Power Supply

Capacitive power supplies are advantageous due to their simplicity and low cost. They are the most straightforward and least expensive AC DC power supplies to manufacture.

Drawbacks of AC DC Power Supplies

Some drawbacks of AC DC power supplies include:

Unregulated Power Supply

Unregulated power supplies are sensitive to variations in mains AC voltage, which can affect the output voltage. Changes in load current can also cause fluctuations in the output voltage due to the inherent impedance in the power supply’s components.

Switched Mode Power Supply

Drawbacks of switched-mode power supplies (SMPSs) include their complexity and the generation of high-frequency, high-amplitude energy. This energy requires a low-pass filter to prevent electromagnetic interference (EMI), manage harmonic frequencies, and mitigate ripple voltages at the switching frequency.

Inexpensive SMPSs may introduce electrical switching noise back into the mains power supply, potentially causing interference with equipment on the same phase, such as A/V systems. Additionally, SMPSs without power factor correction (PFC) can result in harmonic distortion.

Linear Power Supply

Linear power supplies are known for generating significant heat and having lower efficiency, which results in energy loss. A major drawback in high-power applications is their size and weight, attributed to the large transformers and other substantial components required for their construction. Additionally, the design necessitates a heatsink to manage the thermal stress caused by high current output and excessive heat loss during high-power load regulation.

Efficiency is a significant concern with linear power supplies. Their lower efficiency leads to a considerable difference between input and output voltage, which is crucial when evaluating their suitability for a design. Besides efficiency, other factors such as dropout voltage and load voltage should also be considered. Overall, when selecting a power supply for a specific application, it is important to weigh all relevant factors, including efficiency, cost, and size.

Capacitive Power Supply

Capacitive power supplies lack electrical isolation between the input and output. Proper insulation of devices drawing power from these supplies is essential to prevent the risk of electric shock.

Power Supply Comparisons

Comparing linear power supplies to switched-mode power supplies (SMPS) highlights several differences:

Linear Power Supply vs. SMPS

Linear power supplies and SMPS differ in their methods of converting mains AC voltage to output DC voltage. An SMPS uses a power transistor to create high-frequency voltage that passes through a small transformer and is then filtered to remove AC noise. In contrast, a linear power supply uses a transformer to step down the primary AC voltage before filtering to eliminate AC noise.

SMPS units are lighter, more compact, and more efficient, offering a broader input voltage range. They are more durable and generally have higher efficiency compared to linear power supplies, which tend to be larger, heavier, and less efficient.

Linear power supplies typically operate at around 60% efficiency, whereas SMPS can achieve efficiencies of 80% or higher.

Linear power supplies have a longer performance history but come with trade-offs. Ultimately, the choice between linear and SMPS depends on the specific needs and requirements of the application.

Conclusion

AC and DC can be interchanged in order to suit the required input to a device. There are many aspects that have to be considered, from the device’s voltage, current and power limits to the areas in which they are operated to come up with the most appropriate power supply. Also, simple circuits may be able to supply the required power, but they have massive losses and dissipate a lot of heat. The better and more efficient solutions are more complex and consist of more expensive components. AC power supplies are usually preferred in large industries to power heavy load equipment. They are very efficient and minimize losses.

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