A switching power supply is a type of power supply that employs modern power electronics technology to control the duty cycle—the ratio of the time during which a switching transistor is turned on versus off—thereby maintaining a stable output voltage. Typically, a switching power supply consists of a pulse-width modulation (PWM) control IC and MOSFETs. With the steady advancement and continuous innovation in power electronics technology, switching power supply technology itself is also undergoing ongoing innovation. Today, thanks to their advantages of being compact, lightweight, and highly efficient, switching power supplies are widely used in virtually all electronic devices and have become an indispensable power supply solution in the rapidly growing electronics and information technology industry. As China's manufacturing sector continues to develop rapidly and steadily, switching power supplies are gradually gaining prominence on the global stage. Meanwhile, power supply sizes are increasingly trending toward modularity and miniaturization, and their immunity to interference is continually improving.
1 Switching Power Supply
A switching power supply is a general term for switch-mode regulator power supplies, typically referring to AC-DC rectifier circuits that input alternating current and output alternating voltage. In a switching power supply, the output power switch operates in a high-frequency switching mode, resulting in very low self-consumption. As a result, the power supply’s efficiency can reach 75% to 90%, doubling the efficiency of conventional linear regulator power supplies (linear power supplies).
The difference between a linear power supply and a switching power supply lies in the way voltage regulation is achieved: In a linear power supply, voltage transformation can be viewed as adjusting the resistance value—just like changing the operating voltage by adjusting a sliding rheostat. In contrast, a switching power supply can be seen as varying the operating voltage by adjusting the frequency of the switching action.
Switch-mode power supply classification
1. Switching power supply without a power-frequency transformer

The switch-mode power supply without a power-frequency transformer replaces the heavy power-frequency transformer with a compact transformer coil, providing both testing and protection for the power grid. Since the electronic components inside the switch-mode power supply operate in a high-frequency switching mode, their own power consumption is very low, and the power supply’s efficiency is twice as high as that of a conventional linear power supply.

2. Switching power supply, regulated power supply
A switching-mode regulated power supply is an integrated, switch-mode power supply that integrates the PWM control board, output power stage, protection circuitry, and other components into a single integrated circuit. Such power supplies can achieve efficiencies of over 90%, and some even offer continuous adjustment of the output voltage. They are suitable for manufacturing switching power supplies ranging from tens of watts to several hundred watts.
3. Chip-type switching power supply
A chip-based switching power supply integrates all the key power circuitry of a switching power supply into a single integrated circuit (IC), enabling functions such as output protection, duty-cycle modulation, and various types of protective measures, with the fastest response speed. The chip-based switching power supply is compatible with AC inputs ranging from 85 to 265V and 47 to 400Hz, thanks to its input rectifier filter. Moreover, it boasts advantages such as high integration, cost-effectiveness, minimal peripheral circuitry, and superior performance parameters. As a result, it has become the preferred integrated circuit chip for developing medium- and low-power switching power supplies below 600W, high-precision switching power supplies, and modular switching power supply designs.
Basic Principles, Characteristics, and Classification of Switching Power Supplies
Switching Power Supply Operating Mode
Switching power supplies, classified according to their basic operating principles, can be categorized into the following four types:
(1) Pulse Width Modulation (PWM), also known as duty-cycle modulation, achieves the goal of voltage stabilization by adjusting the pulse width. The key component in this approach is the PWM control board. This method is more widely used in power supplies, as it offers a broad range of PWM duty-cycle adjustments. Moreover, PWM can be synchronized with the digital clock of the main system software.
(2) Single-pulse frequency modulation (PFM), also known as pulse-frequency modulation: Similar to duty-cycle regulation, this method achieves the goal of voltage stabilization by adjusting the switching frequency. The key component here is the PFM control board. This approach is particularly suitable for portable devices, as it reduces the static current of the control integrated circuit under low PWM duty cycles and low-frequency conditions.
(3) Single-pulse relative density modulation (PDM), also known as pulse-density modulation: Its advantage lies in its stable duty cycle, allowing precise voltage regulation by adjusting the number of pulses. It employs zero-voltage switching technology, which can significantly reduce power-switching transistor losses.
(4) Hybrid Modulation: This modulation combines PWM and PFM. Both the switching period and the pulse width are adjustable. The PWM control board can be used either as a standalone integrated circuit chip or integrated into a switched-mode power supply, or even embedded directly within the switch-mode power supply itself.
Among these, switch-mode power supplies fall into the category of DC-DC SPWM, while conventional switching power supplies are typically AC-DC SPWM. If you remove only the rectifier and filter stage from the front end, what remains is a DC-DC SPWM; and if you add that rectifier and filter stage back in, you obtain an AC-DC SPWM.
4 Basic Concepts of Switching Power Supplies
The basic concept of a switching power supply consists of the following 7 key components:
(1) Enter the rectifier filter, which includes a rectifying tube and an input coupling capacitor.
(2) A switch-mode power supply with a discrete design, featuring an output power switching transistor and a control board (including an oscillator, a reference voltage source, an error amplifier, and a PWM voltage comparator), as well as an MOSFET.
(3) Drain-clamp maintenance power circuit.
(4) Transformer coil.
(5) Output rectifier filter.
(6) Optocoupler integrated operational amplifier circuit.
(7) Reference-point power circuit: Apply bias voltage to the phototransistor of the optocoupler.
5 Basic Concepts of Scientific Research
The fundamental concept behind the voltage regulator is as follows: When the voltage V rises due to certain conditions, the current flowing through the LED also increases. This increase in LED current, in turn, causes the emitter current of the phototransistor to rise via the optocoupler. As a result, the control terminal current of the TOPSWITCH increases, leading to a reduction in the PWM duty cycle and causing V to decrease—thus achieving the voltage-regulating effect.
6 Summary
From the above, we can see that switch-mode power supplies, as the leading products in today’s power supply industry, have an exceptionally long lifespan and boast significant advantages. From the perspective of their operational principles, numerous factors can affect the quality of switch-mode power supplies. Moreover, enhancements to other protective circuitry further ensure higher safety performance for these power supplies, while the choice of protective devices also influences the responsiveness of the power supply.
Switching power supplies take into account the diverse power requirements of the business world, ensuring both perfect power supply volume and superior safety performance. They guarantee stable power output for various enterprise design boards and power circuits, providing flexible power supply solutions that truly facilitate meaningful interaction between customers and manufacturers.