Association of switching power supply and linear power supply

　　Association of switching power supply and linear power supply

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

　　Principle of switching power supply:

　　Switching power supply mainly includes input grid filter, input rectification filter, inverter, output rectification filter, control circuit, and protection circuit. Here are their functions: Input grid filter: It is used to eliminate interference ripples from the AC grid, such as light switches, household appliances, air conditioners, lightning strikes, etc., and it will also prevent switching power supplies. The generated high-frequency noise diffuses to the grid; input rectifier 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 high frequency AC voltage, and plays the role of isolating the output part from the input power grid; output rectifier filter: it rectifies and filters the high frequency AC voltage output by the converter to obtain the required DC voltage, while also preventing The interference of high-frequency noise on 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 to control the converter to maintain the stability of the output voltage; protection circuit: When the switching power supply is over-voltage, over-current short-circuit, the protection circuit stops the switching power supply to protect the load and the power supply itself. Switching power supply is a conversion device that rectifies AC power to DC power for power supply.

　　The advantages of switching power supply: small size, light weight, easy to carry, high efficiency, strong self-interference resistance, wide output voltage range, especially in Europe and the United States, after the power efficiency and standby power consumption requirements of the switching power supply highlights it Most of the advantages

　　Introduction of linear power supply:

　　The linear power supply is a power conversion device that first passes the alternating current through a transformer to reduce the voltage amplitude, and then rectifies the internal rectifier circuit to obtain pulsed direct current, and then filters to obtain a direct current voltage with a small ripple voltage.

　　The working principle of linear power supply:

　　The linear power supply is actually a high-power transistor in series at the output of the transformer. The control circuit only needs to output a small current to the base of the transistor to control the output of the high current of the transistor, so that the power system is stabilized again on the basis of the transformer. Therefore, the voltage regulation performance of this linear regulated power supply is 1-3 orders of magnitude better than that of a switching power supply or a transformer. However, the power transistor (also known as the regulator tube) generally takes up 10 volts, and every 1 ampere of output current will consume 10 watts of power inside the power supply. For example, the loss of a 500V 5A power supply on the power tube is 50 watts, accounting for the total output 2% of the power, so the efficiency of the linear power supply is slightly lower than that of the transformer.

　　The 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 super-powered power supply to choose from

　　The voltage feedback circuit of the linear power supply is working in the linear (amplified) state, and the voltage of the switching power supply is the voltage adjustment 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 the reference voltage to the comparison voltage amplifier. The output of this voltage amplifier is used as the input of the voltage regulator tube to control the regulator tube to change its junction voltage with the change of 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, by changing the duty cycle. From the perspective of its main characteristics: Although the linear power supply technology is mature, the production cost is not low. Compared with the switching power supply in terms of price, it has lost too much advantage, 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 size of the transformer is relatively large, the efficiency is low, the overall volume is large, and it is relatively heavy. And the input voltage range is required to be high; and the switch The power supply is in a high-frequency state of work. The volume of the transformer is relatively small and relatively light, but the output ripple is larger than that of a linear power supply, but due to its simple structure, low cost and high efficiency (the efficiency of switching power supplies on the market can also reach 90 % Above) has replaced the linear power supply in many occasions, which is the development trend of the power supply in the future.

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