What is the difference between switching power supply and linear power supply?

maart 15, 2020

What is the difference between switching power supply and linear power supply?

Brief introduction of switching power supply:


Our common power supplies, including power adapters and chargers, are switching power supplies. Switching power supply is a kind of power supply that maintains a stable output DC voltage by controlling the time ratio of switching tube on and off. Switching power supply is generally composed of pulse width modulation control IC and MOSFET field effect transistor. The high frequency of switching power supply is the direction of its development. High frequency makes switching power supply miniaturized, and makes switching power supply enter a wider application field, especially in the application of high-tech fields, which promotes the miniaturization and portability of high-tech products change. In addition, the development and application of switching power supply are of great significance in saving energy, saving resources and protecting the environment.


The principle of switching power supply:


A switching power supply mainly includes an input grid filter, an input rectification filter, an inverter, an output rectification filter, a control circuit, and a protection circuit. Let’s introduce their functions separately below: Input power grid filter: It is used to eliminate the interference ripples from the AC power grid such as light switches, switches of household appliances, switches of air conditioners, lightning strikes, etc. It will also prevent switching power supply The generated high-frequency noise spreads to the power grid; input rectification filter: it rectifies and filters the input voltage of the grid to provide DC voltage for the converter; inverter: it is a key part of the switching power supply. It converts the DC voltage into a high-frequency AC voltage, and plays the role of isolating the output part from the input grid; output rectification filter: it rectifies and filters the high-frequency AC voltage output by the converter to obtain the required DC voltage, and at the same time prevents The interference of high-frequency noise to the load; control circuit: detect the output DC voltage, compare it with the reference voltage, and amplify it. Modulate the pulse width of the oscillator, so as to control the converter to maintain the stability of the output voltage; protection circuit: when the switching power supply has overvoltage, overcurrent and short circuit, the protection circuit stops the switching power supply to protect the load and the power supply itself. A switching power supply is a conversion device that rectifies alternating current into direct current for power supply.

Advantages of switching power supply:


Small size, light weight, easy to carry, high efficiency, strong anti-interference, wide output voltage range, especially in Europe and the United States and other regions after the power supply energy efficiency and standby power consumption requirements, switching power supply highlights its advantages

Brief introduction of linear power supply:


The linear power supply is a power conversion device that first passes the alternating current through the transformer to reduce the voltage amplitude, and then rectifies it through the internal rectification circuit to obtain pulsed direct current, and then filters it to obtain a DC voltage with tiny ripple voltage. The working principle of the linear power supply: linear power supply In fact, a high-power triode is connected in series at the output end of the transformer. The control circuit only needs to output a small current to the base of the triode to control the high output current of the triode, so that the power supply system can stabilize the voltage once again on the basis of the transformer. Therefore The voltage stabilization performance of this linear regulated power supply is 1-3 orders of magnitude better than that of switching power supply or transformer. However, the power triode (also known as the adjustment tube) generally takes up 10 volts of voltage, and every 1 ampere of current output will consume 10 watts of power inside the power supply. 2% of the power, so the efficiency of the linear power supply is slightly lower than that of the transformer.

Advantages of linear power supply: stable performance, no interference such as high-frequency ripple.


Disadvantages of linear power supply: heat generation and low energy utilization. There is no choice of super-powerful power supply

The voltage feedback circuit of the linear power supply works in the linear (amplified) state, and the voltage of the switching power supply is adjusted by the tube working in the saturation and cut-off region, that is, the switching state. The linear power supply samples the output voltage and then sends it to the comparison voltage amplifier with the reference voltage. The output of the voltage amplifier is used as the input of the voltage adjustment tube to control the adjustment tube so that the junction voltage changes with the input, thereby adjusting its output voltage. , but the switching power supply changes the output voltage by changing the on and off time of the regulator tube, that is, changing the duty cycle.


From its main characteristics: Although the linear power supply technology is mature, the production cost is not low. Compared with the switching power supply, it has lost too much advantage in price, but the linear power supply can achieve high stability and ripple. Smaller, its own interference and noise are relatively small, but because it works at power frequency (50Hz), the volume of the transformer is relatively large, the efficiency is low, the overall volume is large, and it looks cumbersome. And the input voltage range requires high; and the switch The power supply is in a high-frequency state. The volume of the transformer is relatively small and relatively light, but the output ripple is larger than that of a linear power supply. However, due to its simple structure, low cost, and high efficiency (the efficiency of switching power supplies on the market can also reach 90 %) has replaced the linear power supply in many occasions, which is the trend of future power supply development.


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