The essential difference between switching power supply and linear power supply
1. Switching power supply converts direct current into high-frequency pulse current, stores electric energy in inductance and capacitance components, and uses the characteristics of inductance and capacitance to release electric energy according to predetermined requirements to change output voltage or current; linear power supply does not have high frequency Pulse and storage components, which use the linear characteristics of components to instantaneously feedback and control the input to achieve stable voltage and current when the load changes.
2. The switching power supply can step down or boost the voltage; the linear power supply can only step down.
3. The switching power supply has high efficiency; the linear power supply has low efficiency.
4. The control speed of the linear power supply is fast and the ripple is small; the ripple of the switching power supply is large.
The main working principle of the switching power supply is that the MOS tubes of the upper bridge and the lower bridge are turned on in turn. First, the current flows in through the upper bridge MOS tube, and the storage function of the coil is used to accumulate electric energy in the coil. Finally, the upper bridge MOS tube is turned off, and the lower bridge is turned on. The MOS tube, coil and capacitor of the bridge continuously supply power to the outside. Then turn off the lower bridge MOS tube, and then turn on the upper bridge to let the current enter, and repeat this, because the MOS tubes need to be switched on and off in turn, so it is called a switching power supply.
The linear power supply is different. The linear regulated power supply (LDO) changes and controls its output voltage and current by changing the conduction degree of the transistor. In the linear regulated power supply (LDO), the transistor is equivalent to a variable resistor. , connected in series in the power supply circuit. Since there is no switch to intervene, the upper water pipe has been discharging water. If there is too much water, it will leak out. This is what we often see in some linear power supplies. The MOS tube generates a lot of heat, and the inexhaustible electric energy is all converted into heat energy. From this point of view, the conversion efficiency of the linear power supply is very low, and when the heat is high, the life of the components is bound to decrease, affecting the final use effect. That said, the difference between a switching power supply and a linear power supply is mainly the way they work.
The power device of the linear power supply works in a linear state, that is to say, the power device is always working as soon as it is used, so it leads to its low working efficiency, generally at 50%~60%, and it has to be said that it is very linear power supply. The working method of the linear power supply makes it necessary to have a voltage device to change from high voltage to low voltage. Generally, it is a transformer, and there are others like KX power supply, which then rectifies and outputs DC voltage. As a result, his volume is large, heavy, low in efficiency, and generates a lot of heat. He also has his advantages: small ripple, good adjustment rate, and small external interference. Suitable for analog circuits, various amplifiers, etc.
All regulators use feedback (Feedback) to stabilize the output voltage. The output voltage is sampled through a resistor divider (Figure 6), and this divided signal is fed back to one input of the error amplifier. The other input of the error amplifier is connected to a reference voltage, and the error amplifier will adjust the output to conduct The output current of the Pass Transistor is used to maintain the stable output of the DC Voltage.
