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All colleagues unite and focus their efforts to write a new chapter of developmentWhat are the basic types of switching power supplies?
所属分类： Industry News
发布时间：2020-04-29
Modern Switching power supply There are two types: DC switching power supplies and AC switching power supplies. This discussion focuses primarily on DC switching power supplies, whose function is to convert raw, lower‑quality power sources—such as mains electricity or battery power—into high‑quality DC voltages that meet the requirements of the connected equipment. At the heart of a DC switching power supply lies the DC/DC converter. Consequently, the classification of DC switching power supplies follows that of DC/DC converters. In other words, the categorization of DC switching power supplies is essentially identical to that of DC/DC converters; the classification of DC/DC converters largely defines the classification of DC switching power supplies.
DC/DC converters can be classified into two categories based on whether there is electrical isolation between the input and output: one type, which provides isolation, is called an isolated DC/DC converter; the other type, which lacks isolation, is called a non-isolated DC/DC converter.
Isolated DC/DC converters can also be classified according to the number of active power devices. Single‑switch DC/DC converters include two types: the forward converter and the flyback converter. Dual‑switch DC/DC converters comprise four configurations: the double‑transistor forward converter, the double‑transistor flyback converter, the push‑pull converter, and the half‑bridge converter. A four‑switch DC/DC converter is equivalent to a full‑bridge converter.
Non-isolated DC/DC converters can be classified into three types—single-switch, dual-switch, and four-switch—based on the number of active power devices.
There are six types of single‑switch DC/DC converters: the buck converter, the boost converter, the buck‑boost converter, the Cuk converter, the Zeta converter, and the SEPIC converter. Among these six, the buck and boost converters are fundamental, while the buck‑boost, Cuk, Zeta, and SEPIC converters are derived from them. As for two‑switch DC/DC converters, one notable example is the series‑connected two‑switch buck‑boost converter. Among four‑switch DC/DC converters, the full‑bridge converter is the most commonly used.
When implementing electrical isolation between the output and input, isolated DC/DC converters typically employ a transformer. Because transformers can step up or step down voltage, they help broaden the converter’s range of output applications and facilitate the provision of multiple outputs at different voltages, as well as several outputs at the same voltage.
When the voltage and current ratings of the power switching devices are identical, the converter’s output power is typically proportional to the number of switches employed. Consequently, the greater the number of switches, the higher the DC/DC converter’s output power: a four-switch topology delivers twice the output power of a two-switch configuration, whereas a single-switch topology provides only one-quarter of the output power of a four-switch design.
The combination of non-isolated and isolated converters can achieve certain characteristics that a single converter alone cannot provide.
Based on the direction of energy flow, DC/DC converters are classified into unidirectional and bidirectional types. A bidirectional DC/DC converter can transfer power both from the source side to the load side and from the load side to the source side.
DC/DC converters can also be classified as self‑oscillating or externally controlled. A converter that relies on the internal positive feedback of the switching device itself to sustain periodic switching is called a self‑oscillating converter; for example, the Royer converter is a typical push‑pull self‑oscillating design. In externally controlled DC/DC converters, the control signals for the switching devices are generated by an external dedicated control circuit.
According to the switching conditions of the power transistor, DC/DC converters can also be classified into hard-switching types.
There are two main types: hard-switching and soft-switching. In a hard‑switching DC/DC converter, the switching devices turn on or off while subjected to voltage stress or current flow, resulting in significant overlap losses—known as switching losses—during these transitions. When the converter operates under fixed conditions, switching losses remain constant; moreover, higher switching frequencies lead to greater losses. Additionally, the switching process can excite oscillations in the circuit’s distributed inductances and parasitic capacitances, introducing further losses. Consequently, the switching frequency of hard‑switching DC/DC converters cannot be excessively high. By contrast, in soft‑switching DC/DC converters, during turn‑on or turn‑off, either the voltage across the switch is zero—resulting in zero‑voltage switching (ZVS)—or the current through the switch is zero—yielding zero‑current switching (ZCS). This soft‑switching approach significantly reduces switching losses and suppresses oscillations induced during switching, enabling much higher switching frequencies and paving the way for converter miniaturization and modularization. Power MOSFETs are widely used switching devices due to their high switching speeds, but they also exhibit relatively large parasitic capacitances. During turn‑off, the external voltage charges these parasitic capacitances; if this stored charge is not discharged before turn‑on, it dissipates internally as capacitive turn‑on loss. To mitigate or eliminate such losses, power MOSFETs are ideally operated using zero‑voltage turn‑on (ZVS). Insulated Gate Bipolar Transistors (IGBTs) are composite switching devices. Their turn‑off current tail generates substantial turn‑off losses; however, reducing the current to zero prior to turn‑off can markedly lower these losses. Therefore, IGBTs are best employed with zero‑current switching (ZCS). While IGBTs can also reduce turn‑off losses when turned off under zero‑voltage conditions, MOSFETs cannot avoid capacitive turn‑on losses when turned on under zero‑current conditions. Resonant Converters (RC), Quasi‑Resonant Converters (QRC), Multi‑Resonant Converters (MRC), Zero‑Voltage‑Switching PWM Converters (ZVS PWM), Zero‑Current‑Switching PWM Converters (ZCS PWM), Zero‑Voltage‑Transition PWM Converters (ZVT PWM), and Zero‑Current‑Transition PWM Converters (ZVT PWM) all fall under the category of soft‑switching DC converters. Advances in power electronic switching devices and zero‑switching converter technologies have driven the development of high‑frequency switching power supplies.