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Explain the difference between linear dc power supply and switching dc power supply
- Apr 23, 2018 -

The dc voltage regulator is divided into two types: linear dc power supply and switching dc power supply.

Linear dc power supply refers to the regulated power supply under linear state. In the switching power supply, it is not the same, the switch tube (in the switching power supply, we normally refer to the adjustment tube as the switch tube) is the work in the open and closed two states: open -- the resistance is very small; It's a lot of resistance.

Switching power supply is a new type of power supply. It has the advantages of high efficiency, light weight, rising and falling pressure and high output power. However, because the circuit works on the switch state, the noise is relatively large. Through the following figure, we will briefly discuss the working principle of the step-down switch power supply. As shown in the figure, the circuit is composed of switch K(in actual circuit, triode or field effect tube), continuous diode D, energy storage inductance L, filter capacitor C, etc. When the switch is closed, the power supply is supplied by switch K and inductance L, and some of the energy is stored in inductance L and capacitor C. Due to the self-inductance of the inductance L, after the switch is switched on, the current increases slowly, that is, the output cannot reach the power voltage value immediately. After a certain time, switch, due to the effect of self inductance of the inductor L (you can compare the image of the thought of inductance current inertial effects), will keep the current in the circuit remains unchanged, that is, from left to right to continue to flow. The current flows through the load, returns from the ground, flows to the positive terminal of the continuous diode D, passes the diode D, returns the left end of the inductance L, thus forming a loop. The output voltage can be controlled by controlling the time of switch closure and disconnection (i.e. PWM - pulse width modulation). If the output voltage is detected to control the opening and closing time to keep the output voltage constant, the purpose of stabilizing pressure is achieved.

During the switch closure, the inductor stores energy; When the switch is off, the inductor releases energy, so the inductance L is called the energy storage inductance. The diode D is responsible for providing current access to inductance L during the switching off period, so diode D is called a continuous diode.

In the actual switching power supply, switch K is replaced by triode or field effect tube. When the switch is off, the current is small; When the switch is closed, the voltage is small, so the heating power U * I is small. This is the reason why switch power efficiency is high.

The commonly used chips for switching power are TL494, LM2575, LM2673, 34063,51414, etc.