What are the characteristics of switch-mode power supplies?
Release time:
2020-07-30
With the advancement of electronic technology, the application fields of electronic systems are becoming increasingly broad, and the variety of electronic devices is growing rapidly. Consequently, the requirements for power supplies are becoming more flexible and diverse. The miniaturization and cost reduction of electronic devices have driven power supplies toward development directions characterized by light weight, thinness, compact size, and higher efficiency. Traditional transistor-series-regulated power supplies are continuous-control linear regulators, and this conventional voltage-regulation technology is relatively mature. Moreover, numerous integrated linear regulator modules are already available, offering excellent stability, low output ripple voltage, and reliable performance. However, these traditional regulators typically require bulky and heavy power-frequency transformers for isolation purposes, as well as sizable filters.
With the advancement of electronic technology, the application fields of electronic systems have become increasingly broad, and the variety of electronic devices has grown significantly, placing ever-more flexible and diverse demands on power supplies. The miniaturization and cost reduction of electronic devices have driven power supplies toward development directions characterized by light weight, thinness, compact size, and higher efficiency. Traditional transistor-series-regulated power supplies are continuous-control linear regulators, and this conventional regulator technology is relatively mature. Moreover, numerous integrated linear regulator modules are already available, boasting excellent stability, low output ripple voltage, and reliable performance. However, these traditional regulators typically require bulky, heavy-line-frequency transformers for isolation purposes, and their associated filters are also large in both volume and weight. Furthermore, since the regulating transistor operates in a linear amplification mode, to maintain stable output voltage, a significant voltage drop must be sustained between its collector and emitter terminals, resulting in high power dissipation in the regulating transistor and thus low power supply efficiency—typically around 45%. Additionally, due to the substantial power dissipation in the regulating transistor, high-power transistors must be employed along with sizable heat sinks, making it difficult for such regulators to meet the evolving demands of electronic devices. This has spurred the rapid development of switch-mode power supplies, which feature higher efficiency, smaller size, and lighter weight. Switch-mode regulators employ power semiconductor devices as switches, adjusting the output voltage by controlling the duty cycle of these switches. Taking the power transistor (GTR) as an example: when the switching transistor is fully saturated and conducting, the voltage drop across its collector and emitter approaches zero; and when the transistor is turned off, its collector current becomes zero. As a result, power consumption is minimal, and efficiency can reach as high as 70% to 95%. With lower power consumption, the need for large heat sinks is also reduced. Moreover, switch-mode regulators directly rectify and filter the mains voltage before using a switching transistor to regulate the output voltage—eliminating the need for a power transformer. In addition, the switching frequency typically ranges in the tens of kilohertz, allowing for smaller values of filtering capacitors and inductors. Consequently, switch-mode power supplies exhibit characteristics such as light weight and compact size. Furthermore, thanks to their low power consumption and reduced internal temperature rise, switch-mode power supplies enhance the overall stability and reliability of the equipment. They also demonstrate significantly improved adaptability to grid fluctuations: while conventional series regulators typically allow grid voltage variations within ±10% of 220V, switch-mode regulators can maintain a stable output voltage even when the grid voltage fluctuates between 110V and 260V. (Source: Electronic Products World)
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