Comparison of linear sockets and switch sockets

The switch socket mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit and protection circuit. Their functions are described below.

(1) Input grid filter: Eliminate the interference from the grid, such as the start of the motor, the on/off of electrical appliances, and the interference caused by lightning strikes, and also prevent the high-frequency noise generated by the switch socket from spreading to the grid.

(2) Input rectifier filter: rectify and filter the input voltage of the grid to provide DC voltage for the converter.

(3) Inverter: It is a key part of the switch socket, which converts the DC voltage into a high-frequency AC voltage, and plays the role of isolating the output part from the input grid.

(4) Output rectifier filter: rectify and filter the high-frequency AC voltage output by the converter to obtain the required DC voltage, and at the same time prevent the interference of high-frequency noise to the load.

(5) Control circuit: detects the output DC voltage, compares it with the reference voltage and amplifies it, modulates the pulse width of the oscillator, and controls the converter to keep the output voltage stable.

(6) Protection circuit: When the switching power supply is short-circuited by overvoltage and overcurrent, the protection circuit stops the switching power supply from working to protect the load and the power supply itself. ^

The linear power supply generally sends the output voltage sampling and the reference voltage to the comparison voltage amplifier. The output of the voltage amplifier is used as the input of the voltage adjustment tube to control the adjustment tube to make the junction voltage change with the input, so as to adjust its voltage. The output voltage. But the switching power supply changes the output voltage by changing the on and off time (that is, the duty cycle) of the regulating tube.

The linear socket is similar to the tap water pipe. Since there is no switch intervening, the upper water pipe is always releasing water. If there is a lot of water, it will leak out. This is the M0S tube of some linear sockets that we often see generates a lot of heat. All the unused electrical energy is converted into heat energy. From this point of view, the conversion efficiency of the linear socket is very low, and when the heat is high, the life of the component is bound to decrease, affecting the final use effect. Since the power device of the linear socket works in a linear state, its working efficiency is low, generally 50%-60%. The working method of the linear socket makes it necessary to have a step-down transformer to change from high voltage to low voltage, and then output the DC voltage through rectification, which results in its large size, heavy weight, low efficiency and large heat generation. Of course, the linear socket also has advantages: small ripple, good adjustment rate, small external interference, suitable for use in analog circuits and various amplifier fields.

The power device of the switch socket works in the switching state (one on and one off, the frequency is very fast, the frequency of the general flat switch socket is 100-200kHz, and the module power supply is 300-500kHz). Conductivity materials to make transformers.

In a word, compared with the linear socket, the power conversion efficiency of the switch socket is high, which can reach 65%~90% (the efficiency of the best VICOR switch socket module in the United States is as high as 99%), the heat generation is less, and the power volume coefficient can send 60~10OW It has strong adaptability to large-scale changes in grid voltage, high load stability, output voltage holding time of up to 20ms, switch sockets do not need power frequency transformers, high operating frequency, and required filter capacitors and inductances. Small size, light weight, and fast dynamic response; the switching frequency of open sockets is 20kHz, which is beyond the hearing range of the ear, and there is no annoying noise; the switch socket can use effective power factor correction technology to make the power The factor reaches more than 0.9, and the high one even reaches 0.99. These make switch sockets have largely replaced linear power supplies in the field of communication power supplies.

The main disadvantage of the switch socket is that the circuit is complex and the output ripple is large. At the beginning of the switch socket circuit, its control circuit was composed of discrete components or integrated circuits such as operational amplifiers. Poor performance and other reasons have seriously affected the wide application of switch sockets.

The development of switch sockets depends on the development of components and magnetic materials. In the late 1970s, with the high development of conductor technology, high back-voltage fast power switching tubes made switching power supplies without power frequency transformers rapidly practical. The rapid development of integrated circuits has laid the foundation for the integration of switch socket control circuits. The pulse modulation circuits dedicated to switch sockets have emerged one after another, such as SG3525 and TI494, which provide switching power supplies with integrated control circuit chips with low cost, excellent and reliable performance, and the use of foam, thus making the circuit of the switch socket from complex to simple. At present, the output ripple of the switch socket has been reduced to less than 100mv, and the radio frequency interference and electromagnetic interference have also been suppressed to a very low level. In short, with the development of power electronics technology, the shortcomings of switch sockets are gradually being overcome, and their advantages can be fully brought into play. Especially in the current situation of energy shortage, the high efficiency of switch sockets can make a great contribution to energy saving. It is because of these advantages that the switch socket has flourished.