AC DC Power Supply

Chapter 1:What is the principle of AC and DC power supplies?

This chapter will cover the following topics: the concept of a power supply, the characteristics of AC power supplies, the features of DC power supplies, and the design and function of AC/DC power supplies.

What is a Power Supply?

Power supplies are devices and circuits that transform mains electricity or power from various sources into precise voltage and current levels needed for a specific device. These devices can include everyday household appliances as well as industrial machinery.

Every electrical device has specific voltage and current requirements to operate properly, which are usually provided by the manufacturer or supplier. If these requirements are not met, the device may fail to power on or could suffer damage if the limits are exceeded. Some power supplies are designed to support multiple devices simultaneously and must maintain a stable output regardless of load or input power variations. These are known as regulated power supplies. Conversely, unregulated power supplies have an output that varies with input changes, as the output is a fixed fraction of the input. Power supplies can come in various forms, including external portable units like chargers or integrated components within devices such as televisions and radios. They can convert either AC or DC input into DC or AC output.

What is AC DC Power Supply?

Direct current (DC) flows consistently in one direction. This type of current is commonly supplied by sources like batteries and solar cells.

Alternating current (AC) periodically switches between positive and negative cycles, causing the direction of electron flow to change accordingly.

This describes the type of current that flows from an outlet or generator. Electricity produced at power plants and distributed to homes is delivered as alternating current.

Direct current (DC) maintains a constant voltage, with the current flowing in a single, unidirectional path. In contrast, alternating current (AC) features a voltage that periodically reverses direction, causing the current to change its direction of flow accordingly.

Characteristics of AC DC Power Supply

In alternating current (AC), the direction of current flow reverses continuously. As a result, when components like inductors or capacitors are present in the circuit, there can be a phase shift, causing the current to lead or lag relative to the voltage. In contrast, in direct current (DC), both the current and voltage directions remain constant, leading to consistent behavior in components like coils and capacitors, with no phase shift occurring.

In AC systems, because the direction of current flow alternates, not all current may flow through the load. Some energy can be reflected back and forth between the power source and the load, resulting in reactive power. In DC systems, since the current flows in a single direction, all current flows through the load, and reactive power is not produced, leading to more efficient use of power.

Interrupting direct current (DC) can be challenging. When a constant voltage is applied to DC, especially at high voltages, there is a risk of sparks or electric shocks when the current is interrupted. In contrast, alternating current (AC) periodically drops to zero as the voltage switches between positive and negative, making it generally safer to interrupt, particularly at lower voltages.

To change DC voltage, it is often converted to AC first and then back to DC. This process requires specialized equipment, which tends to be larger and more expensive compared to AC conversion. Direct current is commonly produced by storage devices like batteries and capacitors, making DC ideal for battery-powered products.

While the power supply in most residential settings is AC, electronic devices such as computers and home appliances like televisions use DC. AC from the outlets is converted to DC using rectifiers and capacitors. In data centers, where efficiency is crucial, the use of direct current is being encouraged to minimize losses associated with converting AC to DC.

Construction of AC DC Power Supplies

Each AC-DC power supply has a unique design. Here are some common construction considerations that each design addresses:

Functionality of AC DC Power Supply

AC-DC power supplies can be classified based on various functional features. For example, a regulated power supply maintains a constant output voltage or current despite fluctuations in load or input voltage. In contrast, an unregulated power supply's output can vary significantly with changes in load or input voltage. An adjustable power supply allows the output current or voltage to be set using mechanical controls, such as knobs on the front panel, electronic input controls, or both. Adjustable regulated power supplies offer both regulation and adjustability. Isolated power supplies provide output power that is electrically separate from the input power, unlike other power supplies that have shared connections between the input and output.

Packaging of AC DC Power Supply

Power supplies come in various forms and are categorized accordingly. Bench power supplies are standalone desktop units used for applications like circuit testing and development. An open frame power supply has only a partial mechanical cover, sometimes just a mounting base, and is typically integrated into machines or other devices. Rack mount power supplies are designed to fit into standard electronic equipment racks for protection. Integrated power supplies share printed circuit boards with their load. External power supplies, also known as AC adapters or power bricks, are found in the AC power cords of devices that plug into wall outlets. Wall warts are a type of external power supply built into the outlet plug itself, commonly found in consumer electronics for safety reasons. They step down hazardous 120V or 230V main voltage to safer levels before it reaches the appliance.

Power Conversion Method of AC DC Power Supply

AC-DC power supplies can be broadly categorized into switching and linear types. Linear power supplies process the input voltage directly, with all active power conversion components operating in their linear region. In contrast, switching power supplies first convert the input voltage to DC or AC pulses before processing. This conversion is performed by devices operating mainly in non-linear modes, such as transistors, which spend most of their time in saturation or cutoff. Because devices in linear power supplies operate in a linear region, they dissipate more power as heat. Consequently, switching supplies are generally more efficient than linear supplies, as their components spend less time in the linear operating area.

How AC DC Power Supply Functions

An AC voltage of 230V, or a different value depending on the region, is applied to the input of an AC-DC power supply. Inside the power supply, this voltage is stepped down to the appropriate AC voltage for the supply rating, typically between 9V and 24V for most everyday applications. The AC voltage is then converted to DC voltage. In linear AC-DC power supplies, diodes perform this conversion, while switching mode power supplies use transistors. After conversion to direct current, the voltage is smoothed to eliminate ripples and regulated. Some power supplies may operate without this regulation. The resulting DC power is then used to operate household appliances such as TVs and personal computers.

What to Consider When Choosing an AC DC Power Supply

AC Input Voltage Range (VIN) – This specifies the range of AC input voltage required by the power supply, such as single-phase AC or three-phase AC. Knowing the input AC voltage range of both the intended use and the power supply is crucial for selection. Many appliances operate within a general AC input voltage range of 85 to 264 VAC at 47Hz to 60Hz. Some AC-DC power supplies come with interchangeable blade kits that can be easily swapped to match the regional voltage requirements.

Output Voltage Range (VOUT) – This indicates the range of output voltage needed. For example, if adjustable voltage output is required for applications like LED lighting or measurement and testing, choosing an AC-DC power supply with a variable output range can be cost-effective and convenient. In other cases, a fixed output voltage, such as 12V or 48V, might be required.

Maximum Output Current (IOUT) – It is important to determine the maximum current output needed from the AC-DC power supply, especially in applications where current output may vary significantly. In such cases, power supplies that can be paralleled to increase power capacity might be necessary.

Output Regulation – Some applications may cause high output ripple or fluctuations in current output, particularly with load types like motor drives. Ensuring proper output regulation is crucial for stable performance.

Space and Dimensions – As power supplies become more compact, consider if there is adequate space to accommodate the power supply and any additional components, such as parallel supplies for higher power, conduction plates, or cooling fans.

Enclosure and Cooling With Fans – Determine whether the power supply requires an enclosed fan, conduction cooling, or an external fan to maintain optimal temperature. Many power supplies feature over-temperature protection to prevent damage from overheating.

Temperature Grade – Check if the power supply can withstand extreme temperature conditions, such as -40 degrees Celsius to +50 degrees Celsius.

Derating – Consider how environmental factors like temperature and altitude may affect the power supply’s performance, causing power loss known as derating.

Standards to Meet – Some applications require compliance with specific standards, such as IP20, IP22, or 60601. Many power supplies are tested to meet general customer requirements and may carry certifications like TUV, EN, or UL.

These parameters are essential for selecting the appropriate power supply for an application, depending on the specific needs and requirements.

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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