Brief Analysis of the Working Principle of DC/DC

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Brief Analysis of the Working Principle of DC/DC [Copy link]

According to the working state of the adjustment tube, we often divide the voltage-stabilized power supply into two categories: linear voltage-stabilized power supply and switching voltage-stabilized power supply. A linear voltage-stabilized power supply refers to a voltage-stabilized power supply in which the adjustment tube works in a linear state. However, it is different in a switching power supply. The switch tube (in a switching power supply, we generally call the adjustment tube a switch tube) works in two states: on and off: on - very small resistance; off - very large resistance. A switching power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, voltage step-up and step-down, and high output power. However, since the circuit works in a switching state, the noise is relatively large. Through the figure below, let's briefly talk about the working principle of the buck switching power supply. As shown in the figure, the circuit consists of a switch K (a triode or field effect tube 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 supply supplies power to the load through the switch K and the inductor L, and stores part of the electric energy in the inductor L and the capacitor C. Due to the self-inductance of the inductor L, the current increases slowly after the switch is turned on, that is, the output cannot reach the power supply voltage value immediately. After a certain period of time, the switch is disconnected. Due to the self-inductance of the inductor L (it can be more vividly considered that the current in the inductor has an inertia effect), the current in the circuit will remain unchanged, that is, it will continue to flow from left to right. This current flows through the load, returns from the ground wire, flows to the positive pole of the freewheeling diode D, passes through the diode D, and returns to the left end of the inductor L, thus forming a loop. By controlling the time of switch closing and opening (i.e. PWM-Pulse Width Modulation), the output voltage can be controlled. If the time of opening and closing is controlled by detecting the output voltage to keep the output voltage unchanged, the purpose of voltage regulation is achieved.

During the period when the switch is closed, the inductor stores energy; during the period when the switch is open, the inductor releases energy, so the inductor L is called an energy storage inductor. During the period when the switch is open, the diode D is responsible for providing a current path for the inductor L, so the diode D is called a freewheeling diode. In an actual switching power supply, the switch K is replaced by a triode or a field effect transistor. When the switch is open, the current is very small; when the switch is closed, the voltage is very small, so the heat generation power U×I will be very small. This is why the switching power supply is highly efficient.