Views:101 Author:Site Editor Publish Time: 2019-10-01 Origin:Site
There are two kinds of modern switching power supply, one is DC switching power supply; the other is AC switching power supply. But in fact, AC switching power supply is only a general term, and does not have the actual principle function. Therefore, this paper mainly introduces DC switching power supply.
The core of DC switching power supply is DC/DC converter. Therefore, the classification of DC switching power supply depends on the classification of DC/DC converter. That is to say, the classification of DC switching power supply is basically the same as that of DC/DC converter.
DC/DC converters can be divided into two categories according to whether there is electrical isolation between input and output: one is isolated DC/DC converter; the other is non-isolated DC/DC converter.
Isolated DC/DC converters can be classified according to the number of active power devices. There are two kinds of DC/DC converters with single tube: forward type and flyback type. Two-tube DC/DC converter is divided into double transistor forward converter, double transistor flyback converter, push-pull converter and half-bridge converter. The four-tube DC/DC converter is full-bridge converter.
According to the number of active power devices, non-isolated DC/DC converters can be divided into three categories: single-tube, double-tube and four-tube. There are six single-tube DC/DC converters, namely, buck DC/DC converter, boost DC/DC Converter, buck boost DC/DC Converter, cuk DC/DC converter, zeta DC/DC converter and SEPIC DC/DC converter. Double-tube DC/DC converter is a double-tube series buck-boost DC/DC converter. Four-tube DC/DC converter is commonly used as full-bridge DC/DC converter.
According to the switching conditions of the switch tube, the DC/DC converter can be divided into hard switching and soft witching.
The hard switching DC/DC converter will produce large overlap loss, that is, switching loss, in the process of turning on or off. When the working state of the converter is fixed, the switching loss is also fixed, and the higher the switching frequency, the greater the switching loss. At the same time, the oscillations of distributed inductance and parasitic capacitance of the circuit will be aroused in the process of switching, which will bring additional loss. Therefore, the switching frequency of hard-switching DC/DC converter should not be too high.
The switching mode of the soft switching DC/ DC converter can significantly reduce the switching loss and the oscillation excited in the switching process, so that the switching frequency can be greatly improved. This creates the conditions for the miniaturization and modularization of the converter. MOSFET is a widely used switching device, it has higher switching speed, and also has a large parasitic capacitance. When it is turned off, under the action of external voltage, its parasitic capacitance is full of electricity. If this part of charge is not released before it is turned on, it will be consumed in the device, which is capacitive switching loss. In order to reduce or eliminate this kind of loss, the zero voltage switching mode (ZVS) should be adopted in the power field effect management. The development of the power electronic switching device and the zero-switching converter technology has led to the development of the high-frequency switching power supply.