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The three components of the DC-DC power converter

wallpapers Tech 2021-04-29
1. Switch
No matter which kind of DC/DC converter main circuit uses the component only electronic switch, inductance, capacitor. Electronic switch only quickly opens, quickly off these two states. Only the loss caused by the rapid state transition is small, the current use of electronic switches are bipolar transistors, power field effect tube, gradually popularized IGBT tube, as well as a variety of new high power switching elements with better characteristics.
2. Inductance
Inductance is a commonly used component in switching power supply, because its current, voltage phase is different, so the theoretical loss is zero. Inductance is often used as an energy storage element. It is also used with capacitors in input and output filters to smooth the current. Also known as a choke. It is characterized by the "great inertia" of the current flowing through it. In other words, due to "flux continuity", the current across the inductor must be continuous, otherwise, it will produce a large voltage spike. The inductor of the DC/DC converter is a magnetic component, which naturally has the problem of magnetic saturation. In most cases, the inductor works in a linear region. At this time, the value of the inductor is a constant, which does not change with the terminal voltage and the current flowing through it. However, there is a problem that cannot be ignored in switching power supply, that is, the phenomenon of two distributed parameters (or parasitic parameters) caused by the winding of the inductor of the DC-DC power converter. One is the winding resistance, which is inevitable; The other is the distributed stray capacitance, which depends on the winding process and material. Stray capacitance does not affect much at low frequencies, but gradually increases with frequency, and above one frequency the inductance may become a characteristic of capacitance. If the stray capacitors are integrated into one, the capacitance after one corner frequency can be seen from the equivalent circuit of the inductor.
3. The capacitance
The capacitor is a commonly used component in the switching power supply of DC-DC power converters. Like inductors, it is also a component that stores and transmits electric energy. But the opposite is true for the frequency properties. In application, it mainly "absorbs" the ripple and has the function of smoothing the voltage waveform. Actual capacitors are not ideal components. The series resistance of the capacitor of a DC/DC converter is related to contacts and leads, as well as to the electrolyte. The common composition of the aluminum electrolytic capacitor is Al2O3, and the conductivity is seven times larger than that of air. In order to improve the electric capacity, the aluminum foil surface is made into a regular convex and concave uneven shape, so that the surface area of the oxide film is increased, and the electrolyte can flow on the convex and concave surface. The high-frequency impedance temperature of the ordinary aluminum electrolytic capacitor increases greatly when the high frequency pulsating current increases greatly, which becomes the bottleneck of the long life of the switching power supply. The so-called good capacitance can withstand the current of the back wave, the temperature rise and the ESR value is small.

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