Simple comparison of linear power supply, thyristor power supply, switching power supply circuit

Regarding the circuit structure, whether it is a linear power supply, a thyristor power supply or a switching power supply depends on the specific occasion and is reasonably adopted. These three kinds of circuits are widely used both at home and abroad, each with its own characteristics. The thyristor power supply, with its powerful output power, makes it impossible to replace linear power supplies with switching power supplies. Linear power supplies are widely used for their high accuracy and superior performance. Switching power supplies have reduced the size and weight of the power frequency transformers, and have been reduced in size and weight. They are also widely used in many applications where the output voltage and output current are relatively stable.
First, the circuit structure of the thyristor power supply is as follows:

Generally speaking, the thyristor is a device that controls the voltage. Since the conduction angle of the thyristor can be controlled by the circuit, Therefore, as the output voltage Uo changes, the conduction angle of the thyristor also changes. The voltage Ui applied to the primary of the main transformer also changes.

That is, ~220V mains is only added to the primary of the main transformer after the thyristor control. When the output voltage Uo is high, the conduction angle of the thyristor is large, and most of the mains voltage is put by the thyristor <; (as shown in the figure above), thus the voltage applied to the primary of the transformer, that is, Ui Higher, of course, the output voltage is higher after rectification and filtering. When the output voltage Uo is very low, the conduction angle of the thyristor is very small, and most of the mains voltage is broken by the thyristor. (As shown in the figure below), only a very low voltage is added. The primary of the transformer, that is, the Ui is very low, which of course, after the rectification and filtering, the output voltage is very low.

II. The main circuit of the linear power supply is as follows:

The linear power supply is actually a high-power triode (actually multiple parallel) at the output of the thyristor power supply. The control circuit only needs to output a small current to the triode. The base can control the output current of the triode, so that the power system is regulated once again on the basis of the thyristor power supply. Therefore, the regulation performance of the linear regulated power supply is better than that of the switching power supply or the thyristor power supply. - 3 orders of magnitude. However, the power transistor (also known as the regulating tube) generally occupies 10 volts. Each output of 1 amp is required to consume 10 watts of power inside the power supply. For example, the 500V 5A power supply has a loss of 50 watts on the power tube, accounting for the total output. The power is 2%, so the efficiency of the linear power supply is slightly lower than that of the thyristor power supply.
Third, the main circuit of the switching power supply is as follows:

It can be seen from the circuit that the mains electricity becomes 311V high voltage after rectification and filtering, and becomes pulse after the K1~K4 power switch tube works in an orderly manner. The signal is applied to the primary of the high frequency transformer, and the height of the pulse is always 311V. When K1 and K4 are turned on, the 311V high-voltage current flows into the main transformer primary through K1, and flows out through K4 to form a positive pulse at the primary of the transformer. Similarly, when K2 and K3 are turned on, the 311V high-voltage current flows backward through K3. The primary of the main transformer, flowing out through K2, forms a reverse pulse at the primary of the transformer. In this way, a series of forward and reverse pulses are formed at the secondary of the transformer, which are rectified and filtered to form a DC voltage. When the output voltage Uo is high, the pulse width is wide. When the output voltage Uo is low, the pulse width is narrow, so the switch tube is actually a device for controlling the pulse width.
The difference between switching power supply and linear power supply First, the principle of linear power supply: Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit, protection circuit and so on. The linear power supply first converts the alternating current through the transformer, and then rectifies and filters through the rectifier circuit to obtain an unsteady DC voltage. To achieve high-precision DC voltage, the output voltage must be adjusted by voltage feedback. This power supply technology is very mature and can reach very much. High stability, low ripple, and no interference and noise from the switching power supply. However, its shortcoming is that it requires a large and bulky transformer. The required filter capacitor has a large volume and weight, and the voltage feedback circuit works in a linear state. There is a certain voltage drop on the regulating tube, and a large operating current is output. At this time, the power consumption of the adjustment tube is too large, the conversion efficiency is low, and a large heat sink is also installed. This kind of power supply is not suitable for the needs of computers and other devices, and will be gradually replaced by switching power supplies. Second, the principle of switching power supply: Switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, protection circuit. Their functions are: 1. Input grid filter: Eliminate interference from the power grid, such as motor start, electrical switch, lightning strike, etc., and also prevent high-frequency noise generated by the switching power supply from spreading to the power grid. 2. Input rectifier filter: rectify and filter the input voltage of the grid to provide DC voltage to the converter. 3. Inverter: It is a key part of the switching power supply. It converts the DC voltage into a high frequency AC voltage and acts to isolate the output from the input grid. 4. Output rectification filter: Rectify and filter the high-frequency AC voltage outputted by the converter to obtain the required DC voltage, and also prevent the interference of high-frequency noise on the load. 5. Control circuit: Detects the output DC voltage and compares it with the reference voltage for amplification. The pulse width of the oscillator is modulated to control the converter to keep the output voltage stable. 6. Protection circuit: When the switching power supply has an overvoltage or overcurrent short circuit, the protection circuit stops the switching power supply to protect the load and the power supply itself. The switching power supply rectifies the alternating current into direct current, converts the direct current into alternating current, and rectifies the output into the required direct current voltage. This switching power supply eliminates the transformer in the linear power supply and the voltage feedback circuit. The inverter circuit in the switching power supply is completely digitally adjusted, and can also achieve very high adjustment accuracy. The main advantages of switching power supply: small size, light weight (20 to 30% of volume and weight of linear power supply), high efficiency (generally 60 to 70%, and linear power supply is only 30 to 40%), strong anti-interference The output voltage range is wide and modular. The main disadvantages of switching power supply: Due to the high frequency voltage generated in the inverter circuit, there is some interference to the surrounding equipment. Need good shielding and grounding