Introduction to switching power supply:
Our common power supply, including power adapter and charger, all belong to switching power supply. Switching power supply is a kind of power supply that maintains stable output DC voltage by controlling the time ratio of switching 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 its development direction. The high frequency makes the switching power supply miniaturized, and makes the switching power supply enter a wider application field, especially in the field of high-tech, which promotes the miniaturization and portability of high-tech products. In addition, the development and application of switching power supply is of great significance in energy conservation, resource conservation and environmental protection.
Principle of switching power supply:
Switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit and protection circuit. Here are their functions: input power grid filter: it is used to eliminate the interference ripple from the AC network, such as lamp switch, household appliance switch, air conditioning switch, lightning stroke, etc. it will also prevent the high-frequency noise generated by switching power supply from spreading to the power grid; Input rectifier filter: it rectifies and filters the input voltage of the power grid to provide DC voltage for the converter; Inverter: it is the key part of switching power supply. It converts DC voltage into high-frequency AC voltage, and plays the role of isolating the output part from the input power grid; At the same time, it needs to filter the output voltage of high-frequency rectifier to prevent the interference of high-frequency rectifier voltage to AC load; Control circuit: detect the output DC voltage, compare it with the reference voltage and amplify it. Modulating 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 has overvoltage, overcurrent and 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 alternating current into direct current to supply power.
Advantages of switching power supply: small volume, light weight, easy to carry, high efficiency, strong anti-interference and wide output voltage range. Especially after the requirements for power efficiency and standby power consumption in Europe and America, switching power supply highlights its most advantages
Introduction to linear power supply:
Linear power supply is a power conversion device that reduces the voltage amplitude by passing the AC through the transformer, and then obtains the pulsed DC after being rectified by the internal rectifier circuit, and then obtains the DC voltage with small ripple voltage through filtering
Working principle of linear power supply:
The linear power supply is actually a high-power triode connected in series at the output end of the transformer. As long as the control circuit outputs a small current to the base of the triode, it can control the output high current of the triode, so that the power supply system can stabilize the voltage again on the basis of the transformer. Therefore, the voltage stabilizing performance of this linear regulated power supply is 1-3 orders of magnitude better than that of switching power supply or transformer. For example, the output power loss of the linear transistor is slightly lower than that of the power supply of 500V (for example, the output power of 500V is slightly lower than that of the power supply of 500V).
Advantages of linear power supply: stable performance, no interference such as high-frequency ripple. Disadvantages of linear power supply: heating and low energy utilization. There is no super power supply to choose from
The voltage feedback circuit of linear power supply works in linear (amplified) state, and the voltage of switching power supply is regulated by voltage. The tube works in saturation and cut-off zone, that is, in 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 regulator to control the regulator to change its junction voltage with the change of input, so as to adjust its output voltage. However, the switching power supply changes the output voltage by changing the on and off time of the regulator, that is, changing the duty cycle. From its main characteristics: Although the linear power supply technology is mature, its production cost is not low, and it has lost too much advantage compared with the switching power supply in terms of price. However, the linear power supply can achieve high stability, small ripple, and its own interference and noise ratio are small. However, because it works at power frequency (50Hz), the transformer has large volume, low efficiency, large overall volume and appears bulky And the input voltage range is required to be high; The switching power supply is in the high-frequency state of operation. The volume of the transformer is relatively small and relatively light, but the output ripple is larger than that of the linear power supply. However, due to its simple structure, low cost and high efficiency (the efficiency of the switching power supply on the market can also reach more than 90%), it 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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