Switched Mode Power Supply (SMPS) is a common power converter in modern electronic devices and is widely used in scenarios with different power requirements. According to the different input power types, SMPS can be divided into DC-DC switch mode power supply and AC-DC switch mode power supply. DC-DC switching power supply is responsible for converting one DC power into another DC power of different voltage, while AC-DC switching power supply converts AC power (such as household electricity) into DC power. This article will introduce the working principles of these two power supplies in detail and analyze their application scenarios.

What is a DC-DC switch mode power supply? How does it work?

Definition and basic principle of DC-DC switch mode power supply

DC-DC switch mode power supply is a device used to convert the input DC voltage to the required output DC voltage. For example, you can convert the 24V voltage of the battery to 12V voltage to supply electronic devices that require lower voltage. This conversion not only helps the voltage match the device requirements, but also provides a more stable power output.

Basic working principle

High frequency switching: The working principle of DC-DC SMPS relies on a switching device (such as MOSFET) that switches at a high frequency (tens of kilohertz to several megahertz) to quickly turn on and off the circuit.
Energy storage and conversion: When the switch is turned on, the inductor stores energy; when the switch is turned off, the inductor releases energy to the load through the diode. This efficient energy storage and release mechanism enables the conversion of input voltage to output voltage.
Duty cycle control: By adjusting the ratio of the time the switch is turned on and off (i.e., the duty cycle), the output voltage can be controlled to ensure that the output voltage always meets the demand.
For example, if you have a 24V battery power supply and you want to convert it to 12V to power the device, then by adjusting the duty cycle of the DC-DC switching power supply, this conversion can be easily achieved and the voltage can be kept stable.

Working mode of DC-DC switch mode power supply

There are three common working modes of DC-DC switching mode power supply: buck mode, boost mode, and buck-boost mode.

Buck Converter: Used to convert a higher input voltage to a lower output voltage. For example, converting a 24V battery voltage to 12V. This mode is widely used in automotive electronic equipment and other applications that require voltage reduction from a high voltage power supply.

Working process: When the switch is turned on, the input current is transferred to the load through the inductor, and the inductor stores energy at the same time; when the switch is turned off, the inductor continues to power the load by releasing energy.

Voltage relationship formula

Vout=D×Vin​
Where,
D is the duty cycle.
Boost Converter: Boost mode increases the lower input voltage to the required output voltage and is often used in solar systems or mobile devices. For example, the 3.7V lithium battery voltage is increased to 5V for use in mobile phones or small devices.

Working process: When the switch is turned on, the inductor stores energy; when the switch is turned off, the inductor releases energy to the load through the diode, and the output voltage is higher than the input voltage.

Voltage relationship formula

Vout = Vin/(1−D)​

Buck-Boost Converter: It can both step down and step up, and is suitable for situations where the input voltage may be higher or lower than the output voltage. For example, when the battery voltage fluctuates, it can still maintain a stable output voltage.

Practical Application of DC-DC Switching Mode Power Supply

DC-DC switching power supplies are widely used in many application scenarios:

Portable electronic devices: such as mobile phones and laptops, used to adjust the battery voltage to power different components.
Automotive electronics: Convert the 12V or 24V voltage of the car battery to the voltage required by different devices, such as powering the navigation system or car charger.
Industrial equipment: Provide a stable DC power supply for control systems or sensors that require multiple voltages.

How does an AC-DC switching mode power supply convert AC power to DC power?

Definition and basic principle of AC-DC switching mode power supply

AC-DC switching power supply is a device that converts input AC power to DC power. For example, when the AC power in your home (such as 220V or 110V) is converted to DC power for small appliances (such as LED lights), it is achieved through an AC-DC power supply. This power supply not only ensures that the voltage is converted from AC to DC, but also adjusts the voltage to suit the needs of the electronic device.

Basic working process

Rectification and filtering: First, the AC power is converted into pulsating DC power through a rectifier, and then the ripple in the current is eliminated through a filtering circuit to provide a smoother DC power.
High-frequency conversion and voltage regulation: The rectified DC power is processed by a high-frequency switching converter (such as MOSFET) and the voltage is adjusted to the required value through a transformer. High-frequency switching regulates the voltage, making the power conversion more efficient.
Output rectification and filtering: The current passing through the high-frequency transformer is rectified again and becomes a stable DC power, and finally output to the load device through a filter.

Key components and functions of AC-DC switch mode power supplies

AC-DC switching power supplies smoothly convert AC power to DC power through multiple steps, including:

Rectifier: Converts AC power to DC power.
Filter: eliminates the ripple of the rectified current and provides smoother DC power.
Switching regulator: controls the conversion and output of voltage through switching devices (such as MOSFET).
Transformer: used to step up or down the voltage and provide electrical isolation to ensure safety.

Practical application of AC-DC switching power supply

AC-DC power supply is almost everywhere, mainly used in scenarios where AC power needs to be converted to DC power:

Home appliances: such as TVs, computers, routers and other home appliances, AC-DC power supply converts home AC power into DC power required by the equipment.
Industrial equipment: used to provide stable DC power for large industrial equipment to ensure the normal operation of the equipment under different power grid conditions.
Communication equipment: such as base stations and servers, providing DC power for communication and data transmission equipment.

What is the difference between DC-DC and AC-DC switching power supplies? What are the differences in their application scenarios?

Different input power supply

DC-DC switching power supply: The input is DC power, such as batteries or solar panels, and is usually used in devices that need to convert one DC voltage to another. Commonly found in portable devices, vehicle-mounted equipment and industrial control systems.
AC-DC switching power supply: The input is AC power, such as household or industrial grid power supply, which is used to convert AC power into DC power supply. Typical applications include household appliances, computer power supplies, communication equipment, etc.

Different voltage conversion principles

DC-DC switching power supply: adjust the input current through high-frequency switching, use energy storage elements (such as inductors and capacitors) to achieve voltage conversion, and output stable DC power.
AC-DC switching power supply: convert AC power into DC power through rectification, filtering and high-frequency switching regulation, and achieve voltage rise and fall through transformers to provide stable DC output.

Different application scenarios

DC-DC SMPS: used in battery-powered devices, especially in devices with a large voltage variation range, such as vehicle power systems, portable electronic devices, solar power generation systems, etc.
AC-DC SMPS: mainly used in devices powered by mains power, such as household appliances, industrial equipment and power supply systems of data centers.

How to choose DC-DC or AC-DC switching mode power supply according to actual needs?

Choose according to input power supply

If your power supply is a battery, solar panel or other DC power supply, then you need to choose a DC-DC switching mode power supply. This power supply can effectively convert DC power to another DC voltage required by the device, ensuring that the device can work stably under different voltage requirements. If your input power is AC, such as the grid power supply for home or industrial use, then you need an AC-DC switch mode power supply, which can convert AC power to DC power for electronic devices.

Choose according to output voltage requirements

When you need to step down from a high voltage or step up from a low voltage, you can choose the corresponding DC-DC switch mode power supply. For example, in a car, a 12V battery needs to power some 5V or 3.3V electronic devices, and a step-down DC-DC converter is the best choice. If you have a low-voltage solar panel and want to power a 24V or 48V system, you need to use a step-up DC-DC converter.

For AC-DC power supplies, it is usually necessary to convert 220V AC power for home or industry into low-voltage DC power (such as 5V, 12V or 24V), which is a standard requirement in many home devices and communication equipment. AC-DC power supplies can stably convert high-voltage AC power into the required DC power.

Consider efficiency and power loss

DC-DC and AC-DC switching mode power supplies have higher conversion efficiency than traditional linear power supplies, usually reaching 80% to 95%. Efficient power supplies can not only reduce power waste, but also reduce equipment heating problems and extend equipment life.

Efficiency is particularly important if the system needs to run for a long time. For example, in a battery-powered system, every unit of energy is valuable, so using an efficient DC-DC switching power supply can extend the battery's operating time. If it is an AC-DC power supply in an industrial or data center, choosing an efficient power supply can greatly reduce operating costs and heating problems.

Choose power levels according to application scenarios

Whether it is a DC-DC or AC-DC power supply, there are different power levels to choose from. For smaller portable devices, a low-power DC-DC power supply is usually required, such as a power supply of several watts to tens of watts. In high-power devices, such as communication base stations or servers, AC-DC power supplies of up to hundreds of watts or even kilowatts may be required to power them.

Practical application examples

Application of DC-DC power supply in electric vehicles: A large number of DC-DC power supplies are used inside electric vehicles to regulate battery voltage and ensure stable operation of different components such as LED lights, dashboards, audio systems, etc.
Application of AC-DC power supply in servers: The power supply system of the server usually needs to convert AC power into DC power to provide stable DC power for multiple components such as processors, hard drives and network equipment.

Consider heat dissipation and environmental adaptability

While the switch mode power supply works efficiently, it still generates some heat. Whether it is DC-DC or AC-DC power supply, heat dissipation design needs to be considered. When selecting a power supply, consider whether additional heat dissipation devices such as heat sinks or fans are needed according to the application environment. For power supplies used in harsh environments, waterproof, dustproof, vibration-proof and other characteristics may also need to be considered.

Heat dissipation of DC-DC power supply: Since DC-DC power supplies are usually used in vehicles and portable devices with limited space, heat dissipation issues need special attention. Without good heat dissipation measures, long-term high-power operation may cause the device to overheat and affect its stability.

Heat dissipation of AC-DC power supply: In data centers or industrial equipment, AC-DC power supplies have higher power and are usually accompanied by higher heat, so these devices are usually equipped with active heat dissipation systems, such as fans or liquid cooling systems, to ensure stable operation of the equipment.

Conclusion

DC-DC and AC-DC switched-mode power supplies are an indispensable component of modern electronic devices. Through efficient switching conversion technology, these power supplies can provide stable power support for devices under different voltage and power requirements. DC-DC power supplies are suitable for DC input occasions and are often used in vehicle-mounted equipment, portable devices and solar energy systems, while AC-DC power supplies are mainly used in scenarios where AC power is converted to DC power, such as household appliances, computer power supplies and industrial equipment.

When selecting a switch-mode power supply, it is necessary to comprehensively consider multiple factors such as the type of input power, output voltage requirements, power level, efficiency and heat dissipation requirements. Whether it is a low-power DC-DC power supply for small devices or a high-power AC-DC power supply for industrial systems, reasonable selection and design can improve the performance and stability of the equipment and ensure the safe operation of the system in different environments.

The wide application of switch-mode power supplies enables various electronic devices to work more efficiently, energy-saving and reliably. With the development of technology, future power supply systems will be more intelligent, providing higher power density, stronger environmental adaptability and more flexible voltage regulation capabilities.