According to the adjustment of the working state of the tube, we often divide the power supply into two categories: linear regulator power supply and switching regulator power supply.
The linear regulated power supply refers to a regulated power supply whose regulating tube operates in a linear state. In the switching power supply is not the same, switching (in the switching power supply, we generally call the adjustment tube is called the switch) is working in the open and close two states: open - resistance is small; off - resistance is very Big.
Switching power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, rise, pressure drop, and large output power. However, since the circuit operates in the on-off state, the noise is relatively large. Through the following figure, we will briefly talk about the working principle of step-down switching power supply. As shown in the figure, the circuit consists of a switch K (a triode or field effect transistor in the actual circuit), a freewheeling diode D, an energy storage inductor L, and a filter capacitor C. When the switch is closed, the power is supplied to the load through the switch K and the inductor L, and part of the electrical energy is stored in the inductor L and the capacitor C. Due to the self-inductance of the inductor L, after the switch is turned on, the current increases slowly, that is, the output cannot immediately reach the power supply voltage value. After a certain period of time, the switch is turned off. Because of the self-inductance of the inductor L (it can be considered that the current in the inductor has an inertial effect), the current in the circuit will remain unchanged, that is, continue to flow from left to right. This current flows through the load, returns from ground, flows to the anode of freewheeling diode D, passes through diode D, and returns to the left end of inductor L, thus forming a loop. The output voltage can be controlled by controlling the time for the switch to close and open (ie, PWM - Pulse Width Modulation). If the on-off time is controlled by detecting the output voltage to keep the output voltage constant, this achieves the purpose of regulation.
During the closure of the switch, the inductor stores energy; during the switch off, the inductor releases energy, so the inductor L is called the energy storage inductor. The diode D is responsible for providing a current path for the inductor L during the switch off, so the diode D is called a freewheeling diode.
In an actual switching power supply, the switch K is replaced by a transistor or a field effect transistor. When the switch is off, the current is very small; when the switch is closed, the voltage is very small, so the heating power U&Times; I will be very small. This is why switching power supplies are highly efficient.
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