Similarities and differences between high frequency switching power supply and linear power supply
Features of ordinary power supply:
Usually a linear power supply, a linear power supply refers to a power supply in which the regulator tube works in a linear state. However, this is different from high frequency switching power supplies. The switch tube (in the switching power supply, the adjustment tube is usually called the switch tube) works in two states: on-resistance is very small; off-resistance is very large.
Features of high frequency switching power supply:
High frequency switching power supply usually consists of (pulse width modulation) PWM control IC and MOSFET. With the development and innovation of power electronic technology, switching power supply is mainly used in almost all electronic equipment with the characteristics of small size, light weight and high efficiency, and its importance is obvious.
The high frequency switch mode power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, voltage rise and fall, and high output power. However, since the circuit operates in the switching state, the noise is relatively large. Let's briefly discuss how a step-down switching power supply works.
The circuit consists of a switch K (transistor or field effect transistor in the actual circuit), freewheeling diode D, energy storage inductor L, filter capacitor C, etc. When the switch is closed, the power supply will supply current to the load through switch K and inductor L, and will store a portion of the electrical energy in inductor L and capacitor C with the current. Due to the self-inductance of the inductor L, the current will increase relatively slowly after the switch is turned on, ie the output cannot immediately reach the supply voltage value. After a certain time, the switch will turn off. Due to the self-inductance effect of the inductor L (it can be more clearly assumed that the current in the inductor has an inertial effect), the current in the circuit remains the same, i.e. it continues to flow from left to right, this current flows through the load, from ground The line returns, flows to the anode of freewheeling diode D, flows through diode D, and returns to the left end of inductor L, forming a loop. The output voltage can be controlled by controlling when the switch is closed and open (ie, PWM pulse width modulation). Regulation is achieved when the output voltage is detected to control the on and off times to keep the output voltage constant.
Second, the high frequency switching power supply and the common power supply
Because they have a voltage regulator and use the feedback principle for voltage regulation. The difference is that the high-frequency switching power supply is adjusted through the switching tube, while the ordinary power supply is usually tuned through the linear gain range of the triode.
In contrast, the power consumption of switching power supply is small, the application range of AC voltage is wide, and the ripple coefficient of DC output is better.
The main working principle of the ordinary half-bridge switching power supply is that the switches of the upper bridge and the lower bridge (when the frequency is high, the switches are VMOS) are turned on one by one. First, the current flows in from the upper bridge switch tube, and the storage function of the inductive coil is used to collect electric energy. In the coil, the switch tube of the upper bridge is turned off, and the switch tube of the lower bridge is turned on. The inductor coil and capacitor continue to supply power to the outside. Then turn off the lower bridge switch and turn on the upper bridge to allow current to enter, and the process repeats. Since the two arc extinguishing chambers must be switched on and off one after the other, it is called a switching power supply.
Linear power supplies are different. Since there is no switch action, the upper water pipe always drains. If there is too much, the water will leak out. This usually happens when some linear power regulator tubes generate a lot of heat, and the inexhaustible electrical energy is all converted into heat. From this point of view, the conversion efficiency of the linear power supply is very low, but if the heat generation is high, the life of the components will inevitably be reduced, thus affecting the final use effect.
