Our common power supplies, including power adapters and chargers, are switching power supplies. Switching power supply is a kind of power supply that uses the time ratio of switching on and off to maintain a stable output DC voltage. 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 high-tech field, which promotes the miniaturization and portability of high-tech products. In addition, the development and application of switching power supply are 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 light switch, household appliance switch, air conditioner switch, lightning strike, etc. it also prevents the high-frequency noise generated by the 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 isolates 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, and also prevents 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. Modulating 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 is short circuited due to overvoltage and overcurrent, the protection circuit stops the switching power supply to protect the load and the power supply itself. Switching power supply (SMPS) is a conversion device that converts alternating current into direct current.
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 and other regions, switching power supply highlights its majority of advantages after the requirements for power efficiency and standby power consumption
Introduction to linear power supply:
The linear power supply is a power conversion device that first reduces the voltage amplitude by passing the AC through the transformer, 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:
In fact, the linear power supply is connected with a high-power triode 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 the switching power supply or transformer. However, the power triode (also known as the regulator) generally occupies a voltage of 10 volts. For each output of 1 ampere of current, an additional 10 watts of power will be consumed inside the power supply. For example, the loss of 500V 5A power supply on the power tube is 50 watts, accounting for 2% of the total output power. Therefore, the efficiency of the linear power supply is slightly lower than that of the transformer.
Advantages of linear power supply: stable performance, no high-frequency ripple and other interference. Disadvantages of linear power supply: heating and low energy utilization. There is no super power supply to choose from
The voltage feedback circuit of the linear power supply works in the linear (amplification) state, and the voltage of the switching power supply works in the saturation and cut-off regions, that is, in 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 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 the power frequency (50Hz), the transformer has a large volume, low efficiency, and large overall volume, which makes it cumbersome And the input voltage range is required to be high; The switching power supply is in the high-frequency state. The transformer is relatively small and 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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