Classification of high frequency switching regulated power supplies

Now, with the rapid development of electronic technology and applications, higher requirements are put forward for electronic instruments and equipment, that is, the performance is required to be safer and more reliable, the functions are constantly increasing, the degree of automation is getting higher and higher, and the size is becoming smaller and smaller. This makes it more important to use high-frequency switching power supplies with many advantages. Therefore, high-frequency switching power supplies have been more and more widely used in computers, communications, aerospace, color televisions, etc., and have played a huge role, which has greatly promoted the development of high-frequency switching power supplies. The number of people engaged in research and production in this area is also increasing, and the varieties and types of high-frequency switching power supplies are also increasing. The schematic diagram of various types of high-frequency switching power supplies is shown in the figure. The current topological structure of high-frequency switching power supplies can be divided into the following categories.

Figure Schematic diagram of various types of high-frequency switching power supplies

(1) Classification by excitation method
① Externally excited high-frequency switching power supply. An oscillator with an excitation signal is provided in the circuit,

and the circuit form is shown in Figure (e). ② Self-excited high-frequency switching power supply. The switch tube also serves as the oscillator tube in the oscillator, and the circuit form is shown in Figure (f).

(2) Classification by modulation method
① Pulse width modulation high-frequency switching power supply. The oscillation frequency of the switching circuit remains unchanged, and the output voltage is changed and adjusted by changing the pulse width. Sometimes a feedback closed loop is formed through a sampling circuit, a coupling circuit, etc. to stabilize the amplitude of the output voltage.

② Frequency modulation high-frequency switching power supply. The duty cycle of the switching circuit remains unchanged, and the amplitude of the output voltage is adjusted and stabilized by changing the oscillation frequency of the oscillator.

③ Hybrid modulation high-frequency switching power supply. The purpose of adjusting and stabilizing the output voltage is achieved by adjusting the conduction time and switching frequency of the switching tube.
(3) Classification by the working mode of the switching tube current
① Switching high-frequency switching power supply. The DC is converted into a high-frequency standard square wave by a switching tube, and the circuit form is similar to the externally excited type.

② Resonant high-frequency switching power supply. The switch tube and the LC resonant circuit work together to convert the DC into a standard sine wave, and the circuit form is similar to the self-excitation type.

(4) Classification by the type of switch tube
① Transistor type high frequency switching power supply. A transistor is used as a switching tube, and the circuit form is shown in Figure (d). ② Thyristor type high frequency switching power supply. A thyristor is used as a switching tube. The characteristic of this circuit is that AC power can be directly input from the input end without the need for a primary rectifier. Its circuit form is shown in Figure (c).

(5) Classification by the connection method of the energy storage inductor and the load
① Series type high frequency switching power supply. The energy storage inductor is connected in series between the input and output voltages, and the circuit form is shown in Figure (a).

② Parallel type high frequency switching power supply. The energy storage inductor is connected in parallel between the input and output voltages, and the circuit form is shown in Figure (b).

(6) Classification by the connection method of the switching tube
① Single-ended high frequency switching power supply. Only one switching tube is used in the switching circuit. The characteristics of this circuit are low price, simple circuit structure, but low output power. Its circuit forms are shown in Figures (a), (b), and (d).

② Push-pull type high frequency switching power supply. Use two transistors as switch tubes and connect them into a push-pull power amplifier. The characteristic of this circuit is that the switch transformer must have a center tap. The circuit form is shown in Figure (j).

③ Half-bridge high-frequency switching power supply. Use two transistors as switch tubes and connect them into a half-bridge form. Its characteristic is that it is suitable for occasions with high input voltage. The circuit form is shown in Figure (i).

④ Full-bridge high-frequency switching power supply. Use four switch tubes and connect them into a full-bridge form. Its characteristic is that the output power is relatively large. Its circuit form is shown in Figure (k).

(7) Classification by input and output voltage
① Boost high-frequency switching power supply. The output voltage is higher than the input voltage, which is actually a parallel high-frequency switching power supply.

② Buck high-frequency switching power supply. The output voltage is lower than the input voltage, which is actually a series high-frequency switching
power supply.

(8) Classification by working mode
① Controllable rectifier high-frequency switching power supply. The so-called controlled rectifier type high-frequency switching power supply refers to the use of intercrystalline tube rectifier elements as the power supply for adjusting the switch tube. It can be powered directly by the AC mains power grid, or it can be powered by a transformer after voltage conversion (this power supply method was often used in the early days of the high-frequency switching power supply, but is basically not used at present). The controlled rectifier type high-frequency switching power supply can achieve the purpose of adjusting the output voltage and stabilizing the voltage by adjusting the size of the conduction angle. Its circuit is shown in Figure (h).

② Chopper type high-frequency switching power supply. The chopper type high-frequency switching power supply adopts DC power supply. The input DC voltage is added to the switching circuit, and a unidirectional pulsating DC is obtained at the output end of the switching circuit. Then, a stable DC voltage different from the input voltage is obtained after filtering. The control circuit of the chopper type high-frequency switching power supply samples the output voltage, compares, amplifies, and controls the pulse signal generated by the pulse generating circuit to control the conduction time and cut-off time of the switch tube or the operating frequency of the switch tube, and finally achieves the purpose of stabilizing the output voltage. The overvoltage protection circuit of the circuit also works according to the sampling signal provided by this part. The chopper circuit form is shown in Figure (g).

③Isolated high-frequency switching power supply. This form of high-frequency switching power supply adds a high-frequency transformer (also called a switching transformer) between the input circuit and the inverter circuit. It uses the change of the magnetic field to achieve energy transfer, and there is no direct flow between currents. The isolated high-frequency switching power supply uses DC power supply. After the switching circuit, the DC power can be converted into a high-frequency AC power, which is then isolated and transformed (boosted or stepped down) by the transformer, and then rectified by the rectifier. Finally, multiple sets of DC output voltages with different polarities and values ​​can be obtained. The circuit samples from the output end, amplifies it, and then feeds it back to the switch control end, and controls the operation of the drive circuit, and finally achieves the purpose of stabilizing the output voltage. This form of high-frequency switching power supply is the most widely used in actual voltage stabilized power supplies.

(9) Classification by circuit structure
① Discrete high-frequency switching power supply. The entire high-frequency switching power supply circuit is composed of discrete components. Its circuit structure is relatively complex and its reliability is poor.

② Integrated circuit high-frequency switching power supply. The entire high-frequency switching power supply circuit or part of the circuit is composed of an integrated circuit, which is usually a thick film circuit. Some thick film integrated circuits include switching tubes, while others do not. The characteristics of this power supply are simple circuit structure, easy debugging, and high reliability. This high-frequency switching power supply is often used in color televisions.

The high-frequency switching power supplies described above are all classified from different perspectives and with different characteristics. Although the excitation methods, output DC voltage adjustment methods, energy storage inductor connection methods, switching tube device types, and series and parallel structures of various circuits are different, they can ultimately be attributed to two major categories: series high-frequency switching power supply and parallel high-frequency switching power supply.