There are two modern switching power supplies: one is DC switching power supply; the other is AC switching power supply. The main introduction here is only the DC switching power supply. Its function is to convert the original ecological power supply (coarse power) with poor power quality, such as city power supply or battery power supply, into a high-quality DC voltage (fine power) that meets the requirements of the equipment. . The core of the DC switching power supply is the DC/DC converter. Therefore, the classification of DC switching power supplies depends on the classification of DC/DC converters. In other words, the classification of DC switching power supplies is basically the same as the classification of DC/DC converters, and the classification of DC/DC converters is basically the classification of DC switching power supplies.
DC/DC converters can be divided into two categories according to whether there is electrical isolation between input and output: one is called isolated DC/DC converters with isolation; the other is called non-isolated converters without isolation DC/DC converter.
Isolated DC/DC converters can also be classified according to the number of active power devices. There are two types of single-tube DC/DC converters: Forward and Flyback. Two-tube DC/DC converters include Double Transistor Forward Converter, Double Transistr Flyback Converter, Push-Pull Converter and Half-Bridge Converter Four kinds. The four-tube DC/DC converter is a Full-Bridge Converter.
According to the number of active power devices, non-isolated DC/DC converters can be divided into three types: single tube, double tube and four tube. There are six types of single-tube DC/DC converters, namely, Buck DC/DC converters, Boost DC/DC converters, and Buck Boost DC/DC converters. , Cuk DC/DC converter, Zeta DC/DC converter and SEPIC DC/DC converter. Among the six single-tube DC/DC converters, Buck and Boost DC/DC converters are basic, and Buck-Boost, Cuk, Zeta, and SEPIC DC/DC converters are derived from them. The double-tube DC/DC converter has a double-tube series-connected boost (Buck-Boost) DC/DC converter. Four-tube DC/DC converters are commonly used as Full-Bridge Converters.
When the isolated DC/DC converter realizes the electrical isolation between output and input, it is usually realized by a transformer. Because the transformer has the function of voltage transformation, it is beneficial to expand the output application range of the converter and also facilitate the realization of multiple outputs of different voltages. , Or multiple outputs of the same voltage.
When the voltage and current ratings of the power switch tubes are the same, the output power of the converter is usually proportional to the number of switch tubes used. Therefore, the more the number of switching tubes, the greater the output power of the DC/DC converter. The output power of the four-tube type is twice that of the two-tube type, and the output power of the single-tube type is only 1/4 of that of the four-tube type.
The combination of a non-isolated converter and an isolated converter can obtain some characteristics that a single converter does not have.
According to the transmission of energy, there are two types of DC/DC converters: one-way transmission and two-way transmission. The DC/DC converter with bidirectional transmission function can transmit power from the power supply side to the load side, and can also transmit power from the load side to the power supply side.
DC/DC converters can also be divided into self-excited and other controlled types. A converter that uses the positive feedback signal of the converter itself to realize the self-sustained periodic switching of the switching tube is called a self-excited converter. For example, the Royer converter is a typical push-pull self-excited converter. The control signal of the switching device in the other-controlled DC/DC converter is generated by an external special control circuit.
According to the switching conditions of the switching tube, the DC/DC converter can be divided into two types: Hard Switching and Soft Switching. The switching devices of hard-switching DC/DC converters turn on or off the circuit under the condition of voltage or current flow, so there will be a large overlap loss during the turn-on or turn-off process, the so-called Switching loss. When the working state of the converter is constant, the switching loss is also constant, and the higher the switching frequency, the greater the switching loss. At the same time, the oscillation of the distributed inductance and parasitic capacitance of the circuit will be aroused during the switching process, which will bring additional loss. Therefore, The switching frequency of hard-switching DC/DC converters cannot be too high. The switch tube of the soft-switching DC/DC converter, during the turn-on or turn-off process, or the voltage applied to it is zero, that is, zero-voltage switching (Zero-Voltage-Switching, ZVS), or through the switch tube The current is zero, that is, zero-current switching (Zero-Current·Switching, ZCS). This kind of soft switching method can significantly reduce the switching loss and the oscillation caused during the switching process, so that the switching frequency can be greatly increased, which creates conditions for the miniaturization and modularization of the converter. The power field effect tube (MOSFET) is a switching device with more applications. It has a higher switching speed, but at the same time it also has a larger parasitic capacitance. When it is turned off, its parasitic capacitance is fully charged under the action of external voltage. If this part of the charge is not discharged before it is turned on, it will be consumed inside the device, which is the capacitive turn-on loss. In order to reduce or eliminate this loss, the power FET should adopt the zero voltage turn-on method (ZVS). Insulated Gate Bipolar Transistor (IGBT) is a composite switching device. The tailing of the current during turn-off will lead to a large turn-off loss. If the current flowing through it is reduced to Zero, the switching loss can be significantly reduced, so the IGBT should adopt the zero current (ZCS) turn-off method. When the IGBT is turned off under the zero voltage condition, the turn-off loss can also be reduced, but when the MOSFET is turned on under the zero current condition, the capacitive turn-on loss cannot be reduced. Resonant converter (ResonantConverter, RC), quasi-resonant converter (Qunsi-Tesonant Converter, QRC), multi-resonant converter (Mu1ti-ResonantConverter, MRC), zero voltage switching PWM converter (ZVS PWM Converter), zero current switching PWM Converter (ZCS PWM Converter), zero-voltage conversion (Zero-Vo1tage-Transition, ZVT) PWM converter and zero-current conversion (Zero-Vo1tage-Transition, ZVT) PWM converter, etc., are all soft-switching DC converters. The development of power electronic switching devices and zero-switching converter technology has promoted the development of high-frequency switching power supplies.