What are the advantages and disadvantages of switching power adapters?

Power adapters are essential components for driving various smart electronic devices, and their performance directly affects the technical specifications and the safe, reliable operation of the equipment. Currently, commonly used AC/DC power adapters are divided into two main categories: low-frequency linear power adapters and high-frequency switching power adapters. Low-frequency linear power adapters are rarely used today. Since the key internal components of high-frequency switching power adapters operate in a high-frequency switching state, their efficiency can reach 80% to 90%, with very low power consumption. Their conversion efficiency is nearly double that of ordinary linear regulated power supplies, making them the mainstream product in AC-DC power adapters today.

A switching power adapter consists of several major components, including a full-wave rectifier, switching transistor, drive signal, freewheeling diode, energy storage inductor, and filter capacitor. In fact, the core part of a switching power adapter is the AC-DC converter. Here, we provide the following explanations for AC-DC converters and inverters:

• Inverter: A device that converts DC power into AC power. Inverters are widely used in backup power systems composed of batteries or other DC sources.
• AC-DC converter: A device that converts AC intoDC. This type of equipment is widely used in switching power supplies and adapters.

  

1. Compact size and lightweight: Switching power adapters do not use bulky power-frequency transformers. Additionally, since the power dissipation on the switching MOSFET is significantly reduced, large heat sinks are no longer needed. These two factors contribute to the small size and light weight of switching power adapters.
2. Low power consumption and high efficiency: In the circuit of a switching power adapter, the switching MOSFET alternates between the on and off states under the drive signal, with a very fast switching speed-typically at frequencies above 50 kHz. In some advanced switching power circuits, frequencies can reach several hundred kHz or even close to 1 MHz. This greatly reduces the power dissipation of the switching MOSFET and significantly improves efficiency, which can reach up to 90%.
3. Greatly improved filtering efficiency, reducing the required capacitance and size of filter capacitors: The operating frequency of switching power adapters is typically above 50 kHz, which is more than 1,000 times higher than that of linear regulated power adapters. This increases the filtering efficiency after rectification by nearly 1,000 times. Even with half-wave rectification followed by capacitor filtering, the efficiency is improved by 500 times. For the same ripple output voltage, the capacitance of the filter capacitor in a switching power supply is only 1/500 to 1/1000 of that in a linear regulated power supply.
4. Wide voltage regulation range: The output voltage of a switching power adapter is adjusted by the duty cycle of the drive signal. Variations in the input voltage can be compensated by adjusting the frequency or pulse width. Thus, even when the grid voltage fluctuates significantly, the adapter can maintain a stable output voltage. As a result, switching power adapters have a wide voltage regulation range and excellent stability. Additionally, methods for adjusting the duty cycle include pulse-width modulation (PWM) and frequency modulation (FM). Switching power supplies not only offer a wide voltage regulation range but also provide multiple methods for achieving voltage stabilization, allowing designers to flexibly choose from various types of switching power IC solutions based on practical requirements.

Since the inverter circuit generates high-frequency voltage, it can cause interference to nearby equipment. Proper shielding and grounding are required. In a switching power supply, the power-regulating transistor operates in a switching state, generating AC voltage and current that produce spike interference and resonant interference in other circuit components. Without proper suppression, elimination, and shielding measures, this interference can severely affect the normal operation of the entire device. Additionally, such interference can propagate into the power grid, disrupting nearby electronic instruments, equipment, and household appliances.
 

In fact, highly integrated dedicated chips are now available, simplifying peripheral circuits and even enabling a plug-and-play design. For example, the TOP-series switching power supply ICs (or power modules) only require a few passive components and a switching transformer to form a basic switching power supply.